Continental XO-1430 Development
Part 9: 1 Jan 1937 to 30 Jun 1937
by Kimble D. McCutcheon
Published 2 Oct 2025; Revised 2 Oct 2025

7 Jan 1937. Prescott reported Continental O-1430-1 and Lycoming O-1230-1 engine development status. XO-1430-1 run-in and calibration continued. It had developed 1,000 hp at 3,000 rpm and 47 inHgA manifold pressure. There had been problems getting the lubrication system to work correctly, but Continental thought them largely overcome and expected to begin the 50-hr development test shortly after 15 Jan 1937. After several months of testing, cracks had appeared in the bearing saddles resulting in crankcase replacement with a spare and crankcase redesign to make it stiffer. Another difficulty was failure to maintain sufficient oil pressure at the engine's nose; this was blamed on deflection of the rather thin-walled hollow secondary reduction gear shaft, whose ends assumed an oval shape under load, causing excessive bearing loads. The shaft ends had been reinforced which overcame the deflection. There was also difficulty with the way the engine was attached to its bedplate; this had been remedied so that tests could continue. Continental thought the 50-hr development test could start prior to 1 Feb 1937. A vibration damper had been designed for installation within the supercharger drive gear where it was expected to address single- and two-mode vibration within the crankshaft system. This damper was expected to be installed before the 50-hr test.

Lycoming O-1230 single-cylinder tests were complete and a 2-cylinder dummy test engine was constructed to test the connecting rods prior to their use in a 2-cylinder test engine. The rods, after passing 50 hrs in the dummy engine, were installed in the 2-cylinder engine and run nearly 100 hrs at rated power and speed. Lycoming also contemplated dive testing these parts on both the dummy and 2-cylinder engines. Lycoming had furnished all Van Dykes for the 12-cylinder design, parts had been fabricated; assembly was expected to begin around 15 Jan 1937, and calibration and run-in was to start by 1 Feb 1937. [USNARA RG342 P031241. 7 Jan 1937 Memorandum Report E-57-285-22, Continental O-1430-1 and Lycoming O-1230-1 Engines.]

7 Jan 1937. Tilley and Harold Morehouse met at MatCmd with Prescott and showed preliminary sketches of the proposed 30-cylinder engine incorporating XO-1430-1 type cylinders. One sketch showed roller bearings used to maintain the same cylinder centers used on the XO-1430-1 so that camshafts cam housings and other XO-1430-1 engine parts could be used in the 30-cylinder engine. Another sketch showed a proposed plain-bearing arrangement with cylinder centers increased from 7.188" to 10.500". Prescott thought this cylinder spacing was too great and offered suggestions to make crankshaft and connecting rods more compact. Continental was to make additional studies to determine the best bearing arrangement.

Tilley brought a partially completed run-in test report in order to insure that the data satisfied Air Corps requirements. Prescott thought the report satisfactory and that such data would be useful to the Air Corps. Continental expected to start calibration during the week of 11 January and also expected to be ready to test by that time; the delay was due to labor difficulties at the Bohn Aluminum Company plant. The ALCOA Detroit plant's labor problems had cleared up, which removed the obstacle to sourcing the new crankcase. Continental furnished blueprints of the improved crankcase. Tilley expected that the 50-hr development test would be started with the present crankcase unless the new one was ready. Since the old crankcase had more than 150 hrs, the new crankcase had a good chance of passing the development test since the large circumferential groove on the main bearing shell exterior was being eliminated in the new main bearing shells that were being installed for calibration and development tests; the new bearings had a circumferential groove turned on the bearing shell inside, which had been found to give better lubrication. Continental thought that the external groove in old crankcase was partially responsible for the cracked main bearing bosses.

Tilley asked about contract provisions for teardown inspections during the 50-hr development test and learned that test requirements were the same as for the type tests as defined by Air Corps Specification No. 28143B. Shutdowns caused by equipment, including spark plugs, would not be penalized regardless of the shutdown duration. However, in the case of engine parts failures the 50-hr development test would be considered complete only when all major parts had completed 50 hrs of endurance testing under Specification conditions. The engine was not to be dismantled for inspection without advising MatCmd, and any replacement parts would accumulate time starting at zero. Tilley said that the connecting rod crankpin bearing metal difficulties had been traced to insufficient bearing shell crush in the fork rods; further investigation would determine how much crush was appropriate.

Morehouse produced a blueprint of Continental Dwg SK86 showing a cast piston designed so that it could be forged. This piston would be supplied to MatCmd with the piston pin holes located to give 8.75:1 compression ratio; MatCmd could then use a 0.125" adapter plate to obtain a 7.5:1 compression ratio with the same piston. However, MatCmd preferred the distance from the pin to the skirt to be equal in both special and standard pistons. Morehouse stated that three pistons fitted with rings but no pins could be furnished to MatCmd for $284.50, of which a charge of $75.00 was included to cover the pattern that would become Air Corps property. The drawing showed that rather small ribs were incorporated into the piston head and that the fillets were only 0.125" radius. MatCmd suggested that these radii should be 0.188" instead. The proposed piston incorporated three compression rings in separate grooves and two beveled vented oil scraper rings in one oil ring groove. The design incorporated a reinforcing ring at the skirt end to provide additional stiffness on the open skirt. In a forged piston, this feature would be swaged in after the piston was forged. The design was conventional and incorporated tapering walls behind the rings and in the skirts to improve heat flow from the head to the ring pack, where it would be dissipated to the cylinder wall. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 19 Jan 1937 Memorandum Report E-57-285-54, Conference with Representatives of Continental Motors Corporation Regarding XO-1430-1 Engine. 15 – 17.]

9 Jan 1937. Air Corps Inspector Robert W. Triggs reported that replacement XO-1430-1 parts had been fabricated. XO-1430-1 assembly was to be completed by noon on 9 Jan 1937, at which time testing would continue. All fork connecting rod bearing shells were assembled with 0.0010" to 0.0015" crush. The new accessory housing had more and heavier ribbing for greater stiffness. Oil passages from the pump to Cuno filter sump and then to the accessory drive shaft bushing had a 0.594" diameter instead of the previous 0.500" diameter. The new coolant pump had improved shaft sealing.

[RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 7.]

15 Jan 1937 Progress Report. The single-cylinder engine with a new honed cylinder was run-in for about 3 hrs; bad blow-by occurred at 2,500 rpm and 70 bmep, forcing a stop. The two oil rings in the oil ring groove were removed and two compression rings substituted. This setup was run-in up to 6 inHgG when excessive (5 lb/hr) oil consumption caused the spark plugs to foul. The engine was reassembled with one bevel scraper ring and one compression ring in the oil ring groove. This setup ran for 4 hrs with 1 lb/hr oil consumption, after which the rings were in good condition. This cylinder was removed and a new cylinder/piston combination set up and installed for run-in for use on the XO-1430-1. Run time on the single-cylinder engine parts was as follows:

The XO-1430-1 had a dimensional check on all important parts in accordance with 50-hr test requirements. The accessory case was replaced with a new part with internal bracing ribs. The coolant pump was a new design with a packingless shaft seal. Two reduction gear bearings were replaced with bearings without transverse grooves and with circumferential oil feed grooves and large feed holes. The engine was placed on the dynamometer, run-in for 5 hrs up to 3,000 rpm and 8 inHgG (757 hp), removed for inspection, and found in good condition.

After the engine was reassembled and replaced on the dynamometer, a fuel pump failure delayed testing. The fuel pump was necessary due to fuel flow variation when running from the small weighing tank versus the large feed tank. At 4 inHgG, backfiring occurred due to preignition from the cylinder 5L spark plug, whose mica had failed. This was a Bendix HT 437 A1 plug that had been used for 0:20 hrs at 1,000 hp. All HT 437 A1 plugs were replaced by Champion M-11 plugs. While running at 1,010 hp, a sudden power loss occurred and the engine was removed for inspection. The cylinder 6R piston was scored, apparently due to a deficient oil supply to that cylinder. A new cylinder and piston were run-in on the single-cylinder engine using the 0.188" vented oil ring in place of two bevel oil rings; other cylinders showed no signs of distress. Total engine run time was 215:12 hrs, time above 160 bmep was 2:46 hrs, time under power was 137:18 hrs, and time motoring was77:54 hrs.

Contract W-535-AC-9060 – Hyper Spare Parts: Of the 87 contract items 83 were completed and accepted by the Air Corps Inspector. The supercharger assembly had been received, inspected and was awaiting final acceptance. The reduction gear housing front casting was scrapped and Continental was waiting on another casting. The crankshaft was promised by January 31.

Contract W-535-AC-9295 PO 37-1660 – Hyper #1 Cylinder Assembly: Sample castings showed pattern equipment errors that were subsequently corrected. New castings had been ordered, received and checked. Remaining castings were promised by 31 January. All other items were being manufactured and were to be completed ahead of the cylinder heads.

PO 37-2630 – Connecting Rod Assembly: All items were to be complete by 31 January.

Engineering: Routine drawing changes continued. A layout adapting the test stand mounting setup to use airplane-type mount plates was completed. Connecting rod and Hyper No. 1 cylinder assembly Van Dykes were sent to MatCmd. Drawings were complete and parts ordered to conduct corrosion tests on cylinders and jackets exposed to ethylene glycol. Layouts for a larger engine using XO-1430-1 cylinders and valve gear continued. Replacement part lists and Government Liability to 15 Jan 1937 were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 29 – 32.]

No other XO-1430-1 damage or parts failure was apparent. Engine reassembly was held up pending the coolant system investigation. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 8 – 9.]

20 Jan 1937. Morehouse met with Prescott at Wright Field and relayed the information that XO-1430-1 cylinder 6R was slightly scored, damaging the piston enough to require replacement, but he thought the cylinder could be repaired by honing in order to proceed with the calibration run. Continental thought the scoring might have been due to temporary faulty coolant distribution or local boiling. Morehouse asked for a copy of Air Corps Technical Report, Serial No. 3873, giving all known Prestone characteristics.

Morehouse reported intake pipe crushing and cracking because of the packing used at the manifold ends. The original intention was to make these pipes individually removable, but the need to do this had not arisen and Continental thought a better packing could be used while still being able to remove the entire induction system. Prescott approved this change because the new packings were the same type used on all radial engines. Morehouse stated that half of the new crankcase being fabricated under Contract W-535-AC-9060 had been lost due to excessive porosity, which was uncovered during machining operations. This would cause a delay in furnishing all parts call for on the contract. Prescott said that extremely poor metal had been found by X-ray and sectioning of the failed reduction gear housing, and that the porosity made the castings unsuitable for use in highly stressed parts like crankcases. MatCmd believed that the excessive porosity was caused by the metal being poured at too high a temperature in order to ensure the mold would be completely filled. A formal report on this investigation's findings would be forwarded to Continental for information and guidance.

Morehouse stated that 5 satisfactory Hyper No. 1 cylinder head castings had been received and were in process. The first cylinder barrels had been lost in heat treatment, but new barrels were in process. The first connecting rod had also been lost during machining and a new one was in work. These delays would prevent filling the order before 28 February.

The XO-1430-1 was to have been run in on 19 January and been ready for calibration on 20 January; Continental would telephone MatCmd when the calibration was complete so as to expedite MatCmd presence for the 50-hr endurance test. Morehouse brought additional sketches of the 30-cylinder engine incorporating two main bearing types. One showed a roller bearing with construction similar to the Allison X-4520 except that the crankcase was made in two halves instead of the barrel crankcase construction that had been used on the X-4520. With this construction it was possible to duplicate the XO-1430-1 cylinder-center distance, which both Continental and MatCmd believed to be advantageous as it allowed interchangeable camshafts and cam housings between the 12- and 30-cylinder engines. The sketches with plain main bearings showed cylinder center distances of 8.625" instead of the 7.188" XO-1430-1 dimension; this would mean new camshafts and cam housings. The roller bearing scheme had been submitted to the Norman-Hoffman Company for bearing size recommendations. Further 30-cylinder study was planned and Continental would offer MatCmd a program once the details were ironed out. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 29 Jan 1937 Memorandum Report E-57-285-55, Conference with Representatives of Continental Motors Corporation on XO-1430-1 Engine. 20 – 22.]

Testing was suspended while several exhaust stacks were repaired; the engine was removed from the stand and cylinders removed for inspection. Cylinder 6R, which was scored during the previous run, was in excellent condition. However, it was impossible to say whether the improvement was due to better cooling or better lubrication due to substitution of the 0.188" slotted oil ring for the two 0.094" bevel scraper oil rings previously used. The piston and cylinder were reassembled without change.

The two 0.094" bevel scraper oil rings on cylinder 3L had been assembled on the piston upside down, which probably accounted for the high oil consumption (35 lb/hr) at 1,000 bhp. The cylinder 2R exhaust valve spring was broken. A further attempt to complete Contract W-535-AC-8131 Item 1 was planned for 23 Jan 1937. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 18 – 19.]

29 Jan 1937. Kinnucan met at MatCmd with Air Corps Resident Inspector Silas Snyder and civilian engineers H.W. Lake and Prescott. Kinnucan and Snyder brought with them the XO-1430-1 crankcase, which had recently been recalibrated; upon examination two minute cracks were discovered in the main bearing boss adjacent to the front main bearing. One crack appeared to have resulted by extremely high hydraulic pressure exerted by oil upon the bearing shell dowel pin top; the pin had by this manner been pressed back into the dowel hole with such force that the metal covering the dowel inner end had been cracked slightly. MatCmd proposed that measures be taken immediately to prevent this problem's recurrence by using a stepped dowel pin constructed so it could not be pressed into the crankcase. Kinnucan also proposed that the dowel holes in the bearing shells be drilled from the outside as blind holes rather than penetrating the inner bearing surface, in order that hydraulic pressure might be eliminated on the dowel pin top. It was noted that the improved main bearings had not yet been installed and it was recommended that the newer main bearing type having no external oil groove be installed at this time. Kinnucan stated that these bearings were expected within the next few days and would be available for installation. In this matter, he said that perfect interchangeability had apparently been attained with the crankcases and bearing shells and that in the present engine the bearing shells had been moved from the old crankcase to the new without reboring or fitting and had functioned nominally. This was an important step in engine maintenance since it was no longer necessary to bore the main bearings in place.

Reduction gear housing X-rays taken by MatCmd were examined; the X-rays and crankcase sections had revealed excessive porosity in certain inaccessible casting locations. However, test samples subjected to tensile tests met Air Corps Specifications. MatCmd wanted to X-ray other crankcases to see whether the porosity was a common defect. It was also noted there was no assurance that such a complicated casting, cast from the same material, would produce castings as perfect as those comprising test bars. The entire subject of casting and foundry practice was tabled for further investigation.

Kinnucan said that Continental was still experiencing difficulty with the XO-1430-1 intake pipes; several had been too long and were shortened, but nothing seemed to the crushed and cracked intake pipes. A design was in work that would use packings similar to those used in air-cooled engines in the XO-1430-1 manifold. The lower ratio supercharger drive gears were nearly ready for installation. In connection with this, it was very desirable to use a later-design NA-F7F carburetor that would give a ~0.75 inHgG restriction instead of the 2 inHgG restriction of the present NA-F7C carburetor. This change would cost MatCmd $175.00. Kinnucan requested that a Type A-1 generator control panel, Specification 32016, be furnished for the Eclipse Type E-5 generator so that the generator could be operated loaded during the 50-hr development test. This generator control panel was given to Kinnucan for transportation to Continental.

Kinnucan reported continued difficulty with the bearing metal on the connecting rod bearing shell exterior. This was a matter of securing a proper quench on the bearing metal both inside and outside of these shells; to date the manufacturer of these bearings had been unable to supply satisfactory bearings. Other bearings were on order from another manufacturer that claimed satisfactory results by slightly changing the lead-bronze composition on the bearing exterior. Kinnucan asked if MatCmd was interested in testing cadmium-silver bearings in the MatCmd single-cylinder test engine at Continental. Continental would do this at no cost to MatCmd; he was furnished a drawing of the special test engine bearing.

The matter of 8.75:1 compression ratio pistons was again discussed, with special reference to internal piston design and piston ring setup. Piston data being evaluated at MatCmd had been used to produce skirt and land diameters and MatCmd wanted this and its piston ring setup incorporated into this piston's design.

Kinnucan reported studying the use of airplane-type mount plates for the XO-1430-1 on the dynamometer; this was impossible without completely rebuilding the test stand piping. MatCmd did not view this as vital for the 50-hr development test and suggested that this consideration be abandoned in favor of concentrating on the development test. Kinnucan stated that a small sleeve in the starter-generator drive had been experiencing failures of a small lug that entered one spline in the starter-generator drive bevel gear. MatCmd suggested that several lugs be provided to enter each spline thereby distributing the load instead of concentrating it on one. Kinnucan left calibration data taken during the final XO-1430-1 runs. These showed a 1,013 bhp corrected power at 2,988 rpm and 1,008 bhp observed power, a 188.4 psi bmep, and a 0.554 lb/hp/hr bsfc. This appeared to be the best power setting, but a reading taken at 762 actual bhp at 2,746 rpm showed a 0.545 lb/hp/hr bsfc. He said that with its surprisingly satisfactory mixture distribution, the XO-1430-1 would probably operate on a leaner mixture. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 2 Feb 1937 Memorandum Report E-57-285-56, Conference on January 29, 1937 on Continental O-1430-1 Engine. 24 – 27.]

Coolant Flow versus Temperature Rise

31 Jan 1937 Progress Report. Single-cylinder tests of coolant flow through the new cylinder head and barrel were made, with each measured separately with calibrated orifices. Separate temperature rise data was also collected by thermocouples placed between double gaskets at the coolant inlet and outlet elbows. A 3.6 gpm flow in the barrel and 11 gpm flow in the head gave a 12°F separate temperature rise. A flow versus temperature rise curve was prepared that showed not only the single-cylinder data but also the XO-1430-1 data without flow restricting orifices. The venturi for this flow measurement had a 196 gpm maximum range, which was given at 2,300 engine rpm. Extrapolation to 3,000 rpm indicates a 250 gpm flow, and on this basis, together with observed pressures, the restricting plate orifice diameter was calculated to be 0.500" for the head and 0.286" for the barrel.

The XO-1430-1 was run-in for 4:20 hrs up to 3,000 rpm and 0 inHgG, the nose section removed, the new eccentric bushing inspected and found in good condition. Since the previously-reported piston seizure might have been caused by defective coolant circulation and the circulation was in excess of contract requirements, coolant flow restricting plates were placed on the cylinder coolant inlets. The engine was placed on the dynamometer and run up to 1,000 rpm when a stop was caused by a broken exhaust pipe. Oil consumption during this run appeared to be about 35 lb/hr; the engine was removed for inspection, but nothing explained the high oil consumption. The engine was reassembled, replaced on the dynamometer and run at 1,000 hp for 9 minutes when an exhaust pipe broke due to failure of a stud on cylinder 1R; it was then removed for repair. Oil consumption again was about 35 lb/hr; further investigation showed an oil cooler leak. After the leak was repaired, the engine was again placed on the dynamometer and calibration attempted. After 18 minutes at nearly 1,000 hp, another exhaust pipe failure caused a forced stop. It was discovered that one magneto was timed 10° late. After repairs, calibration was completed. Continental Report #141 covered run-in and development up to the time of calibration; Report #142 covered the calibration. (Neither report was found in the files.)

The engine was in good condition after the calibration runs except that main bearing shell dowel pins had sunken into the crankcase, probably because of oil film pressure, which had caused minute cracks in the bearing seat. Total engine time was 228:17 hrs, time above 160 bmep was 3:53 hrs, time under power was 143:30 hrs, and time motoring was 81.54 hrs.

Contract W-535-AC-9060 – Hyper Spare Parts: Of the 87 items 86 were complete and accepted. Ohio Crankshaft Company was machining the crankshaft and had promised it for 10 February.

Contract W-535-AC-9295 PO 37-1660 – Hyper #1 Cylinder Assembly: Two cylinder assemblies were to be ready for shipment on 15 February and the order balance on 1 March.

PO 37-2630 – Connecting Rod Assembly: This part was scrapped due to a manufacturing error. A new one was in work and promised for 19 February.

Engineering: Routine drawing changes continued. Work on large engine layouts using XO-1430-1 cylinders and valve gear had continued. A piston to facilitate compression ratios up to 8.75:1 had been detailed. Replacement part lists and Government Liability to 31 Jan 1937 were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 36 – 41.]

6 Feb 1937. Triggs reported that the XO-1430-1 had been assembled with main bearings featuring blind dowel holes. After a 5-hr run-in to 750 bhp at 0 inHgG boost, the engine was disassembled, found in good condition, and was being reassembled; the 50-hr endurance run was to be started on Monday morning, 8 Feb 1937. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 23.]

Continental wanted information on the necessity of including a hydraulic propeller control in the 50-hr development test, in view that MatCmd did not consider the current hydraulic propeller control design acceptable, and that it jeopardized a heavily-loaded bearing in the reduction gear. Continental proposed instead to furnish the hydraulic propeller control and governor according to the latest Government specifications on the second engine to be procured. At the time the contracts were signed, no hydraulic control was available and thus it was not included in the design requirements. The present design was included at Continental's expense to increase the engine's value to both military and commercial customers. Since this design was completed, hydraulic control construction was revised to provide positive two-way operation and also incorporate governor controls. Continental thought it was in the Government's interest to proceed with dynamometer testing without the hydraulic control.

Tilley asked about the status of run-in and calibration test reports; he was told they were satisfactory and would be approved upon receipt of a supplemental letter giving the oil consumption results as obtained in the 5-hr run. The maximum oil consumption during this run was approximately 0.021 lb/hp/hr, a value considered satisfactory by MatCmd. Sketches and drawings for the proposed 24- and 30-cylinder incorporating XO-1430-1 parts were examined. Tilley stated that he would be ready to make a preliminary presentation of a program, including cost estimates, to develop a 2,000 – 2,500 hp engine on 12 Feb 1937. He also stated that bearing manufacturers had made estimates on bearings suitable for the 30-cylinder engine main bearings, and that they preferred ball bearings such as were used in large two-row radial engines

[RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 13 Feb Memorandum Report E-57-285-57, Conference at Continental Motors Corporation on XO-1430-1 Engine. 53 – 55.]

13 Feb 1937. Triggs reported that the XO-1430-1 had operated for 5 hrs continuously on 8 Feb 1937; 0.5 hr was at rated speed and power (3,000 rpm and 1,000 bhp), while 4.5 hrs was at 97 % rated speed and 90% rated power (2,910 rpm and 900 bhp). Operating conditions were the same as those previously reported for engine calibration except that the specific oil consumption was 0.21 lb/hp/hr at 3,000 rpm and 1,000 bhp, and 0.105 lb/hp/hr at 2,910 rpm and 900 bhp. When inspected, there were cracks in the main bearing diaphragms adjacent to the main bearing bosses; one crack was in the left case half, the other in the right. Several exhaust valves had small burned spots on their faces. Cylinder 1L exhaust valve leakage had just started. Reduction gear teeth had apparently been slightly crowding one another. Under magnaflux inspection the propeller shaft showed slight crack indications originating from an accessory drive shaft drive gear bolt hole. These conditions were discussed with Prescott on 10 February. Necessary changes were in process, crankcase pattern changes were about 90% complete and some cores were in process. New castings were expected on Wednesday, 17 February. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 28.]

15 Feb 1937 Progress Report. No single cylinder engine running occurred during this period.

The XO-1430-1 was reassembled with new main bearings that did not have the dowel holes through the shell but that a circumferential oil spreader groove on the bearing journal side. Bearings #4 and #7 were not changed at this time; #7 was not changed because of oil feed requirements to other engine parts and #4 was not changed because a new one was unavailable. The engine was reassembled with jacketed cast aluminum exhaust elbows with 2.5" diameter flexible tube extending to the floor. The carburetor was replaced with the modern Stromberg Model NA-F7F. The engine was placed on the dynamometer and run in for 5 hrs up to 700 hp. Inspection revealed the main bearings were in good condition, the crankcase cracks and dowel holes had not changed, and one cam housing cover that had been cracked and leaking for some time was replaced with a new one; a new Type B-2A, PN 194 vacuum pump was assembled to the engine.

The engine was returned to the dynamometer and after a short run the vacuum pump was replaced because of excessive oil in the air output. A run was started under contract endurance conditions and continued for 5 hrs; a graphic log was attached. The period shown is between inspection 38 and 39. The 37-38 period was the running documented in this reports first part. During this run the oil consumption for the 30 minutes at 1,000 hp averages 21.5 lb/hr; for the 4.5 hrs at 900 hp the oil consumption averages 10.5 lb/hr. Fuel consumption for this run was just under 0.52 lb/hp/hr. The throttle was not wide open for the 1,000 hp run, which gives an supercharger intake pressure of -2.5 inHgG. Despite satisfactory operation throughout this period, it was considered advisable to inspect the engine before further operation, so the engine was removed from the dynamometer and disassembled.

The crankcase was cracked in several transverse diaphragms adjacent to the main bearings. Some exhaust valve seats were eroded. Revised crankcase castings were promised during the week of 15 March. Total engine time to date was 240:10 hrs, time above 16 bmep was 8:56 hrs, time under power was 157:50 hrs, and time motoring was 82:20 hrs.

Contract W-535-AC-9060 – Hyper Spare Parts: Of the 87 contract items, 86 were complete and accepted. The crankshaft was completed and was awaiting journal bore oil plugs.

Contract W-535-AC-9295 PO 37-1660 – Hyper #1 Cylinder Assembly: Two of the five assemblies were complete and were to be shipped to Wright Field on 17 February. Two additional sets were ready for assembly. The last set awaited a head casting as only four good casting had been received from ALCOA; the remaining castings were rejected for porosity; three more castings were promised for 18 February.

PO 37-2630 – Connecting Rod Assembly: This connecting rod was completed and was to be shipped to Wright Field on 17 February.

Contract W-535-AC=9639 0 PO 37-3435 – Crankcase Assembly: The pattern equipment was modified and castings were in work. In view of the failure that occurred during the 5-hr run, all work was delayed. Further changes had been made to eliminate the last failure; these were agreed upon in a conference with Prescott. Pattern changes were in process, and castings from revised equipment were promised for the week of 15 February

Engineering: Routine drawing changes continued. Layouts for a larger engine using existing cylinders and valve gear continued. This work had been reviewed by MatCmd. Blueprints had been marked up to permit pattern changes and casting procurement. Layouts of a new intake pipe gland nut for use with the present intake pipes had been made; a single pipe could still be removed if required. The new scheme was the same as used in most radial engines and should eliminate intake pipe leaks and failures. Replacement part lists and Government liability to 15 Feb 1937 were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 42 – 52.]

Kinnucan said that the costs for this engineering change were actual costs to Continental Motors Corporation for making this change. He also confirmed figures on the possible development of 24-, 30- and 36-cylinder engine incorporating the O-1430 type cylinders and valve gear. These figures were included in the MatCmd's Memorandum Report E-57-285-58 dated 2 Mar 1937. Kinnucan stated that the three 24-, 30- and 36-cylinder designs had many parts in common, including cylinder assemblies, cam box assemblies, ignition, piston assemblies, and cam box accessories. In addition to these features, the 24-cylinder design would also include the same connecting rods and crankshafts as the XO-1430-1. This would make available with a minimum of new parts, engines of 1,000, 2,000 and 2,500 hp. Kinnucan emphasized the fact that the Continental figures submitted were based on labor and materials cost as of 19 Feb 1937. He stated that the industry was facing an unknown future because of strikes and rising material markets as of 19 Feb 1937. Figures were, therefore, subject to revision when negotiations were entered into between the Government and Continental.

MatCmd's chief interest centered on a 36-cylinder engine, and MatCmd suggested that a proposal with drawings in sufficient detail to outline the proposal should be presented to MatCmd in the near future. (AUTHOR'S NOTE: This is a classic example of requirements creep; Continental, which was struggling to produce a workable 1,000 hp engine, was now answering the mail for engines that were at as much as three times the original output.)

Kinnucan brought with him two new XO-1430-1 crankcase halves that had been rough-machined and X-rayed by MatCmd to detect porosity and hidden defects in order that expansive labor loss might be avoided it defects were uncovered during fabrication. All parties decided, because of these X-rays, that one case half was probably acceptable for finish machining, but that the other half was excessively porous and should be rejected. Kinnucan stated that a new casting would be started immediately while machining on the good casting proceeded. [USNARA RG342 P031149. 2 Mar 1937 Memorandum Report E-57-285-59, Conference with Representative of Continental Motors Corporation on XO-1430-1 Engines.]

28 Feb 1937 Progress Report. The single-cylinder engine was run at 3,000 rpm and 211 imep while head coolant flow was reduced by closing an outlet valve. Normal flow showed a 235°F coolant-in temperature and a 250°F coolant-out temperature. The flow was reduced until the coolant-out temperature was 286°F; a thermocouple in the coolant near the head top adjacent to the large pipe plug and toward the exhaust side showed nearly identical temperatures. This indicates adequate head coolant circulation.

New XO-1430-1 crankcases were in work as described below under Contract W-535-AC-9639. The exhaust valves were sent to Wilcox-Rich for re-facing. Instruments and the test setup were adjusted to reduce the errors prevalent during the calibration and 5-hr test. The dynamometer beam error was found to be within the Toledo scale and was reduced from a 1.3% maximum to <0.5%. Thermometer were adjusted so that the errors were <1°F. Some instruments showed as high 10°F error. The fuel weighing scale was adjusted to reduce the error from 1.5% to <0.2%. The engine was repainted and prepared for photographs; project delays would have occurred if the photography had taken place earlier.

Contract W-535-AC-9060 – Hyper Spare Parts: Of the 87 contract items, 86 were complete and accepted. The crankshaft was awaiting oil plug completion; completion was expected on 8 March.

Contract W-535-AC-9295 PO 37-1660 – Hyper #1 Cylinder Assembly: Two cylinder assemblies had been completed and shipped to Wright Field. The balance of this order was to be shipped on 20 March. A deviation regarding extra spark plug holes in two assemblies had been received, executed and returned to MatCmd.

PO 37-2630 – Connecting Rod Assembly: This item was complete and shipped to Wright Field. A deviation regarding bolt holes and bolt was received, executed and returned to MatCmd.

Contract W-535-AC-9639 – PO 37-3435 – Crankcase Assembly: Casting from the revised patterns were received and partially machined, taken to Wright Field, X-rayed, and were being finish-machined back at Continental. The factory promised completion on 16 April, but every effort was being made to finish earlier.

Engineering: Routine drawing changes continued. Crankcase detail drawings, which included revisions, were complete, as were intake pipe gland detail drawings. Replace parts and Government liability to 28 Feb 1937 were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 57 – 61.]

13 Mar 1937. Triggs reported that good progress was being made machining the new XO-1430-1 crankcase, although the shop was only working two shifts; the tense Detroit labor situation made it inadvisable to work overtime. The two crankcase halves were to be bolted together on 15 March. The completed crankcase was promised for 16 April. No XO-1430-1 running occurred that week; the first engine photographs were unsatisfactory and a new set was taken while the engine was unassembled. Engine assembly resumed on 12 March, but before it could be completed the new reduction gear housing was doweled to the old crankcase to save time doing this later. This new reduction gear housing was to be used with the new crankcase. Check runs with and without the torsional damper were planned for the following week. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 56.]

15 Mar 1937 Progress Report. The single-cylinder test engine was built up with three 0.125" bevel compression rings; the top ring bevel faced away from the piston crown and the other two bevels faced toward the crown. The 0.188" vented oil control ring was replaced by two 0.094" compression rings to facilitate run-in. No rings were pinned. An exhaust pipe using a rubber hose as the flexible member with water injection producing a circumferential water spray on the rubber was made up and installed. This engine was run for 6 hrs without mishap, and further running was planned to determine the durability of the new features.

About 15 XO-1430-1 photographs were taken in various positions. Triplicate bound sets were delivered to MatCmd. The exhaust valves sent for re-facing were back from Wilcox-Rich. Engine reassembly had started and the new vibration damper was to be included. This new equipment would be run-in and tested with the old crankcase while awaiting the new crankcase.

Contract W-535-AC-9060 – Hyper Spare Parts: All contract items were completed and accepted.

Contract W-535-AC-9295 PO 37-1660 – Hyper #1 Cylinder Assembly: Four assemblies had been completed and two shipped to Wright Field; three more were expected to ship on 20 March.

Contract W-535-AC-9639 – PO 37-3435 – Crankcase Assembly: The crankcase was in work and completion promised on 16 April. However, every possible effort was being made to finish early. Main bearings on order from the Bohn Aluminum Company were held up due to a sit-down strike. Additional bearings had been ordered from Federal Mogul and Allison Engineering Company to ensure bearings were on hand when the crankcase was ready.

Engineering: Routine drawing changes continued. Layouts and detail drawings were made to provide flexible rubber XO-1430-1 test stand mountings; these parts were supposed to be in the factory during the week of 22 March. Layouts and load analyses continued on the 24- and 30-cylinder engines. No additional replacement parts were required for this period. A recapitulation was provided. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 62– 64.]

20 Mar 1937. Triggs reported that the new crankcase had been bolted together and that the main bearings had been finished-bored. Apparently the porosity in these bearing saddles was machined off, but this could not be confirmed until the case was inspected. Triggs estimated that the case would be completed about 5 Apr 1937. The XO-1430-1 had not been run during the past week. Assembly was delayed by the new reduction gear housing doweling. Later, when the engine was partially assembled, it was discovered that several bushings required for the torsiometer drive were not standard size to fit the new drive gears. Re-boring these delayed engine assembly until Saturday 20 March. MatCmd pointed out to Continental that this was an avoidable delay and that his work could have been done during the past month when the engine was idle. Two spare crankcase castings had been received and sent to MatCmd for X-ray. Rubber mounting pads for the test stand were fabricated and would be used for some tests prior to the 50-hr endurance test. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 65.]

27 Mar 1937. Triggs reported that the XO-1430-1 was assembled on 24 Mar 1937 with the same parts used for the February 5-hr endurance test, with the exception of the torsiometer drive, which was installed for the first time. A 2-hr run was made on 25 Mar 1937, and two runs were made on 26 March. A 2-hr run-in was made on 25 March, and on 26 March two runs were made, the first one with the torsiometer mounted at the left camshaft rear. Torsiographs were made at speeds ranging from 400 to 3,000 rpm and with varying loads at each speed. The second run was made with the torsiometer mounted on the starter base and driven by a special gear installed for that purpose. Several torsiographs were made at 2,900 rpm and 900 bhp and 3,000 rpm and 1,000 bhp. When these runs were complete the vibration damper was installed. Continental expected that comparative runs would be completed on 22 March. Torsiograph photostats were to be sent to MatCmd at a later date. Work on the new crankcase continued without delay. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 66.]

31 Mar 1937 Progress Report. Run-in of the piston and ring setup described in the 15 Mar 1937 Progress Report was complete. During the run-in latter part, oil consumption was high. It was later discovered that the scavenge line had a cracked bushing that leaked oil and probably accounted for this high oil consumption. Before this was discovered, the oil ring was changed from two compression rings to a vented oil ring. During the run with this ring setup, oil consumption was again high, presumably for the same reason as before. This oil ring was replaced by a two-piece bevel scraper ring that was the same used in the XO-1430-1. At the run's beginning a cracked scavenge line bushing leaked oil and was replaced. Before this was discovered, the oil ring was changed from two compression rings to a vented oil ring. At the run's beginning the cracked scavenge line bushing was discovered. After repairs, a run was made during which the oil consumption was about 0.5 lb/hr/hr, not withstanding the high oil squirt. During a 3-hr run where these figures where obtained there were several periods of bad blow-by. Inspection showed the top ring badly worn. Single-cylinder part time was as follows:

Three bound assembled XO-1430-1 photograph sets were delivered to MatCmd. The engine was reassembled to recheck torsional vibration characteristics; the crankshaft had been dynamically rebalanced by the Ohio Crankshaft Company. After a 2-hr run-in the torsiometer was installed on the right (flywheel) end. Cards were taken covering spreads from 450 to 3,000 rpm. The torsiometer was installed to record crankshaft vibration and cards were taken at 2,930 rpm at 900 hp and at 3,000 rpm and 1,000 hp. The engine was then disassembled to install the friction damper. It was discovered that the new reduction gears did not run freely with their mating gears, so all reduction gears would be replaced. Torsional vibration results were to be separately reported. Engine total time was 243:57 hrs, time above 160 bmep was 8:59 hrs, time under power was 160:11 hrs, and time motoring was 83:46.

Contract W-535-AC-9295 PO 37-1660 – Hyper #1 Cylinder Assembly: All contract items were completed and shipped to Wright Field.

Contract W-535-AC-9639 – PO 37-3435 – Crankcase Assembly: The crankcase was promised for 5 April. Main bearings were being made by the Allison Engineering Corporation, Bohn Aluminum Company and Federal Mogul Corporation. The main bearings on order from Bohn Aluminum were delayed due to a sit-down strike. Bearings from Federal Mogul were promised for 5 April.

Engineering: Routine drawing changes continued. Bearing loads were calculated for a large-size Hyper (24-, 30-, 36-cylinder) engine. Crankshaft torsional characteristics were estimated. Reduction gear and cylinder arrangement layouts were made and were to be separately submitted. Replacement part lists and Government liability to 31 Mar 1937 were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 67 – 71.]

2 Apr 1937. Tilley and Kinnucan met with Maj Page, Prescott and Chenoweth at MatCmd where Tilley said that the newly redesigned crankcase was nearly ready for installation in the XO-1430-1. The present hold-up were the main and connecting rod bearings due to a sit-down strike at the Bohn Aluminum Company; Allison was unable to furnish similar bearings on short notice. In order to expedite the 50-hr development test Federal Mogul cadmium-silver bearings had been procured and were being installed, at least for temporary running. Tilley pointed out that the XO-1430-1 unit main bearing loads were from 950 psi to 1,100 psi, and connecting rod loads were 1,600 psi. These loads were within allowable Babbitt bearing limits so there was no reason to expect them to be unsuccessful in the XO-1430-1; cadmium-silver bearings had a considerably higher melting point and better operating characteristics at high temperatures than the Babbitt bearings.

Tilley said that the new crankcase looked much better than the previous design and that he hoped that the former weak points had been fixed. He stated that current foundry practice straightened the crankcases by pulling them into shape and then striking them with a sledge hammer to set the metal and remove enough of the twist to allow them to clean up. MatCmd found this procedure objectionable and suggested an alternative method whereby the crankcases would be pulled into shape by a fixture, raised in temperature and then cooled in that position. Tilley agreed to investigate this.

Kinnucan showed torsiographs taken at the XO-1430-1 camshaft rear that showed gradually increasing torsional vibration amplitude up to about 6° due to the excitation from the cams up to 2,200 crankshaft rpm. At this point the amplitude broke sharply and reduced for the remainder of the run to about 2°. Kinnucan said that the proposed test procedure including checking the camshaft vibration characteristics with the flywheels removed, and also the possibility substituting flywheels of greater mass in order to reduce the peak from 2,200 rpm to a considerably lower value.

Kinnucan asked about the adoption of an AN standard 4-bolt fuel pump flange with the bolts equally spaced. Capt Johnson said that a new standard was to incorporate four equally spaced bolts starting with 1938 procurements. Kinnucan reported difficulty with vacuum pump oil consumption, saying that the present installation blew out 2 – 3 gallons of oil per hour! Capt Johnson said that only 1 pint per hour was allowed and that the vacuum pump installation was incorrect or insufficient sealing existed where the vacuum pump drive exited the crankcase. He furnished a blueprint showing correct vacuum pump installation and associated piping; Kinnucan planned to investigate this and correct any difficulties. [USNARA RG342 P031147. 7 Apr 1936 Memorandum Report E-57-285-60, Conference with Representatives of Continental Motors Corporation on XO-1430-1.]

2 Apr 1937. Tilley and Kinnucan met with Maj E.R. Page, Chenoweth and Prescott concerning 3,000 hp engine concepts. Tilley stated that considerable preliminary design work had been done incorporating 6 cylinder banks identical to the XO-1430-1 banks, into a large 3,000 hp engine. He showed sketches giving the approximate outline. The proposed 36-cylinder engine used two crankshafts, possibly identical to the XO-1430-1 shafts. Proposed reduction gear sketches were shown and for a unit estimated to weigh about 450 lb. Kinnucan left a reduction gear blueprint with MatCmd, along with bearing load diagram showing main and articulated rods in an engine incorporating 3 banks in a W configuration for each crankshaft. These bearing loads had been found to be much more uniform that those with 60° or 180° V engines, with main and connecting rod maximum values only slightly higher.

Tilley asked abut the procedure by which a project presentation could be made to MatCmd and was told that this study needed to be carried to the point that the contractor was reasonably sure it could build such an engine, with enough sketches to show the engine type proposed, plus time and material cost estimates, broken down into development stages. Tilley pointed out that this large engine would leverage Continental's already considerable effort; starting with a fully-developed cylinder would eliminate much delay and expense. Tilley said that studies would continue as outlined and that Continental would offer MatCmd a formal proposal as soon as possible. [USNARA RG342 P031145. 7 Apr 1936 Memorandum Report E-57-285-61, Conference with Representatives of Continental Motors Corporation on 3,000 hp Engine.]

6 Apr 1937. Triggs reported that the two spare XO-1430-1 crankcase castings had been X-rayed by MatCmd and found to be in the best castings yet produced. There was one small porous spot in an unstressed section. PO 37-3435 crankcase machining had been completed, was being inspected, and would then have the cylinder studs installed. Continental had conceded to the local union's 40-hr work week demand, which would severely impact the rapid project completion; the union objected to staggering engine crew hours and there was not enough work for two crews. Given these obstacles, Triggs thought it improbable that the 50-hr endurance test would start before 18 Apr 1937. The rubber-mounted test stand setup was expected to be complete before the next engine run. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 72.]

10 Apr 1937. Triggs reported difficulties that had delayed XO-1430-1 assembly. The reduction gear train could not be assembled with the vibration damper as it was impossible to install a locking device at the quill shaft inside end. This was remedied by installing a 0.312" through bolt with appropriate washers to lock the quill from the outside. This was a temporary expedient and some other design might be worked out and submitted to MatCmd later. Continental intended to start the 50-hr test with new connecting rod bearings but the Allison ones were undersized and had insufficient crush; they were returned to Allison and the old rod bearings used. The cadmium-silver bearings were being fitted for crush. Although the engine crew was working overtime, the various fitting jobs on the new crankcase would delay engine assembly until about 14 April. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 74.]

15 Apr 1937 Progress Report. The worn single-cylinder top ring, reported last period, was replaced by another of the same type. The two-piece American Hammered bevel oil control ring was replaced with a slotted oil drain ring. After a 4.5-hr run-in the engine was run at 3.5 hrs at 3,000 rpm and 211 imep, 1 hr at 3,250 rpm and 211 imep, and 1 hr at 3,000 rpm and 240 imep. During this run the oil consumption was about 2 lb/hr. Inspection showed the top ring to be slightly feathered and that the gap had increased by 0.007" The feather was removed and the engine run 1.25 hrs at 3,000 rpm and 211 imep when work stopped due to the XO-1430-1 becoming available. During this run the rubber exhaust pipe was used. Examination after the running showed the water exhaust annulus to be clogged with dirt. This annulus was reworked to increase it from 0.010" to 0.015". Run time for the single-cylinder engine parts was as follows:

The XO-1430-1 was reassembled with a new crankcase, a friction vibration damper, new reduction gears, new Federal Mogul cadmium-silver crankshaft bearings, and new intake pipe seals at the intake manifold. The rubber engine mounting that went between the engine mount plates and cast iron sub-base was completed and the engine set up on the dynamometer. No running was accomplished during this period.

Contract W-535-AC-9639 – PO 37-3435 – Crankcase Assembly: The crankcase was completed, accepted and installed in the engine.

Contract W-535-AC-9785 – PO 37-4358 – Replacement Parts: Of the 47 contract items, 45 were complete and accepted. Item #26, accessory housing, Dwg #503535, was in work and expected to be complete on 15 May. Item #31, Dwg #505534, bracket, accessory drive housing, was held up pending engine operating results.

Engineering: An adapter had been made to enable torsiometer cards to be taken from the camshaft front or rear end. A separate vibration study report was planned. Castings for the high-compression piston were rejected due to porosity; replacements were promised for the first part of May. Replacement part lists and Government liability to 15 Apr 1937 were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 83 – 91.]

17 Apr 1937. Triggs reported that the XO-1430-1 was mounted on the test stand on 16 April after drilling new holes in the base for the rubber mounting. Measurements were taken with a lever and weights to determine the rubber mounting deflection before running. Two 8-hr shifts starting 14 April were required for this. New main bearing run-in was to start on 19 April. After receiving the presumably undersize connecting rod bearings that Continental had returned, Allison claimed they were satisfactory, but a recheck by Continental found they still were undersize. One bearing and the Continental checking fixture were sent to Allison. Except for the engineering data that could be obtained, little was to be gained by starting the endurance test with old connecting rod bearings. However, Continental stated the endurance test would start as soon as run-in and inspection were complete. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 75.]

24 Apr 1937. Triggs reported that the XO-1430-1 was motored over for about 1 hr and run for a short time under its own power on 17 Apr 1937. Run-in occurred on 19 and 20 April, with the last 0.5 hr at 750 bhp and 3,000 rpm. The rubber mounting seemed to improve the vibration characteristics, but the vibration damper did not appear to improve the already-documented vibration amplitude. Continental hoped that the damper would be useful at higher powers. During this run some crankshaft and camshaft torsiographs were taken; the camshaft torsiograph, taken on a camshaft front without a flywheel, broke the torsiometer springs. The engine was then removed for inspection, which occurred on 21 April. Some cylinder skirts were slightly touching the new crankcase ribs and enough metal was removed from the ribs to provide 0.032" skirt clearance. A slight feathering was noticed on the reduction gears. Both rocker box covers were cracked; one had about 190 hrs and the other only a few. Continental was getting quotes on a die to make these covers of stamped duralumin. All other parts were in good condition.

On 23 April, a 2-hr run was made with the intention to achieve full power for 15 minutes. A reduction gear knock developed and the reduction gear housing was removed. Nothing was found amiss, but it was postulated that an oil lock formed by vibration damper installation caused the knock. This was relieved by drilling oil drain holes. The engine was again being mounted on the stand and a 5-hr run was planned for 26 April. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 76.]

28 Apr 1937. Triggs reported that the XO-1430-1 had been brought up to rated power on 26 Apr 1937 was brought up to rated power for a 5-hr run consisting of a 0.5-hr run at 1,000 bhp and 3,000 rpm followed by 4.5 hrs at 900 bhp and 2,900 rpm. Before this run the blower ratio was changed from 6.45:1 to 6.1:1). It was possible to produce rated power with this blower ratio but with very little power reserve; fully opening the throttle increased manifold pressure by 1 inHgA. On 27 April, the engine was torn down for inspection. Dwg #503603 bearing, propeller shaft inner had worked out 0.063" causing enough heat to begin melting this bearing's lead layer as well as that of the Dwg #500629, bearing, reduction gear pinion. Both were being replaced. Two connecting rod bearings were found in poor condition and new ones secured from Bohn Aluminum Company would be satisfactory for at least one 5-hr period. Three piston ring pins were broken. The remaining engine parts were in good condition. The Allison Engineering Company admitted the first connecting rod bearing set it furnished were indeed undersize; a new set was promised by about 4 May 1937. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 79.]

30 Apr 1937 Progress Report.

Single-cylinder test engine running resumed using the same piston/ring combination described in the pervious progress report. When 5:05 hrs had been obtained the cylinder barrel cracked in the same place as previously reported; this cylinder was of the thin-wall type preceding those presently used in the XO-1430-1. The test engine was prepared for return to MatCmd for modernization. Run time for the single-cylinder engine parts was as follows:

The XO-1430-1 was run-in on the 500 hp propeller load curve. Crankshaft torsiograph cards were taken over a speed range based on propeller load to absorb 600 hp at 3,000 rpm; the friction damper did not appreciably change the vibration amplitude. The torsiometer was then placed on the camshaft rear with the camshaft flywheel left in place; cards were taken starting at 3,000 rpm, progressively decreasing. The results were the same as previously taken with the rpm increasing. The camshaft flywheel was removed with the intention of getting camshaft torsiograph cards starting at low speed and increasing. However, there were several torsiometer spring failures and the run was discontinued to repair the torsiometer.

The engine was removed from the dynamometer for partial inspection to determine the new crankcase and reduction gear condition. Most cylinder skirts were in contact with the crankcase diagonal ribs behind the main bearing bosses; these were filed down to ensure skirt clearance. The reduction gears were in good condition, but the tooth contact was not uniform. The engine was reassembled, returned to the test stand, and run for about 1 hr at light load when an unusual noise in the reduction gear was heard. A few small bits of wood were noticed between the gear teeth, and there was no escape or oil leakage from bearings inside the propeller shaft. To relieve this oil trap, 0.125" holes were drilled through the washers within the pinion to permit oil to pass through the quill shaft and into the crankcase. The supercharger drive gear ratio was changed to reduce the supercharger speed from 19,200 rpm to 18,000 rpm. A new set of Champion M-11-A spark plugs was installed and the engine returned to the dynamometer.

After warming up, the engine was run for 5 hrs under contract conditions of 0.5 hr at 1,000 hp and 4.5 hrs at 900 hp. The principal difference between this and previous runs was a reduction of about 3 inHgG boost required to get 1,000 hp due to the changed supercharger drive ratio. The engine was removed and inspected. Three reduction gear bearings for the pinion and propeller shaft showed localized signs of overloading. There was further deterioration of the connecting rod bearing surface. The vibration damper disks showed slight scuffing. The engine was reassembled with a damper made of woven asbestos or clutch lining, two new connecting rod bearings, and modified reduction gear bushings with more clearance and axial grooves placed in the bearing adjacent to the damper to ensure oil flow over the damper. The engine was placed on the dynamometer and run-in for three hours. XO-1430-1 total time was 265:56 hrs, time above 160 bmep was 14:16 hrs, time under power was 177:19 hrs and time motoring was 88:37 hrs.

Contract W-535-AC-9785 – PO 37-4358 – Replacement Parts: Of the 47 items 45 were complete and accepted. Item #26, accessory housing, Dwg #503535, was in work and expected to be complete on 20 May. Item #31, Dwg #505534, bracket, accessory drive housing, was held up pending engine operating results.

PO 37-4716 – Piston Assemblies: Castings for 15 pistons had been made, rough machined and rejected for pinhole porosity. At ALCOA's request, Continental ordered semi-permanent mold pattern equipment to obtain better castings. New castings from this equipment were promised on 10 May; if the castings were satisfactory, pistons were to be complete by 15 May.

Engineering: Layouts were being made rearranging the oil system to provide low pressure for the rear end and accessories and to provide an auxiliary high pressure oil line to the front reduction gear bearings. Replacement part lists and Government liability up to 30 Apr 1937 were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 92 – 98.]

6 May 1937. Triggs reported that the XO-1430-1 was mounted on the test stand to run-in the new bearings on 1 May 1937. On 3 May a 3-hr run was made, the last hour consisting of 0.5 hr at 1,000 bhp and 3,000 rpm and 0.5 hr at 900 bhp and 2,900 rpm. During this run a considerable coolant loss occurred and the engine was shut down to investigate. No problems were found with the cooling system, so the engine was removed from the test stand for inspection. Each cylinder was tested in 250°F Prestone with air pressure applied to the coolant jackets; no leaks were found. Both Dwg #503726 camshaft housings had cracks extending from the extreme outer edges at the 0.25" studs towards the center, about 2" long. Two cracks were visible in one housing and six in the other. The worst one was replaced from stock. Corrective measures to strengthen the camshaft housings were being prepared for MatCmd approval. The single-cylinder test engine on loan from MatCmd was expected to be shipped back on 7 May 1937.

[RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 80.]

7 May 1937. Triggs reported that the XO-1430-1 was started for a 5-hr run on 6 May. After running for 5 min at 1,500 rpm a reduction gear bearing seized. Reduction gear housing tear-down was difficult as the quill shaft splines were stuck. A large piece of the outer propeller shaft bearing lead-bronze lining had loosened from its steel back and rotated to cover the oil hole to the inner propeller shaft bearing, which then seized. The two damaged bushings were and replaced. The pinion gear shaft running in the seized bushing was damaged but could be repaired. The quill shaft was damaged during removal and was to be replaced from stock. The engine was expected to be again running on 8 May 1937. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 81.]

14 May 1937. Triggs reported that the XO-1430-1 was run for 6 hrs on 12 May, 4 hrs of which was at 900 bhp and 2,900 rpm, completing the 5-hr period from 3 May, 0.5 hr at 1,000 bhp and 3,000 rpm, and 1.5 hr at 900 bhp and 2,900 rpm. It was shutdown after this 2-hr run due to carburetor ice; it was a very damp day. Prior to this run, two new bushings were installed in the reduction gear housing and run-in for about 4 hrs. After these runs, inspection revealed that an oil pump idler gear was stuck to its shaft, causing the shaft to rotate with the gear; very little damage was done to the oil pump housing. The cadmium-silver crankshaft thrust bearing was damaged on one thrust face, and would be replaced with additional clearance. Several piston ring pins were broken. One piston had no ring pins and its piston rings showed only slight feathering but were in satisfactory condition; more pistons without pins would be used during the next run. The new Allison connecting rods bearings would be used on the next run. The cracked camshaft housing was in no worse condition than at the previous inspection. At the suggestion of an ALCOA representative, the holes in the camshaft cover were enlarged by 0.031" to allow more thermal expansion freedom. The engine was expected to be again running on 17 May 1937. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 82.]

15 May 1937 Progress Report. The single-cylinder engine was returned to MatCmd on 6 May 1937 for crankcase top half replacement.

XO-1430-1 run-in was continued up to rated speed after which the engine was run 1.25 hrs on endurance of which 0.5 hrs was at 1,000 hp. During the last part of this run the coolant flow decrease and other observations indicated coolant was escaping the system. The engine was removed from the dynamometer, taken apart, and the cylinders tested with 20 psi air inside the coolant jacket with the whole cylinder submerged in 250°F Prestone; no cracked cylinders were found. The inner propeller shaft bearing, Dwg #503603 was displaced toward the engine about 0.063"; this bearing was replaced with more shrink. During the warm up before the last run the right distributor failed and was replaced. The right cam housing was replaced due to cracks.

The engine was replaced on the dynamometer and run-in for 35 minutes. During preliminary running the engine load fell off suddenly. The inner and outer propeller shaft bearings had failed. It was believed that the Dwg #503604 outer bearing had its lead-bronze break loose from the steel backing and clog the oil passages that fed the inner Dwg #503603 bearing. These bearings were from Bohn Aluminum and were replaced with parts from the same source. Orders were placed to Allison Engineering Company for replacements. The engine was reassembled, placed on the dynamometer and run-in for 4 hrs. The nose section was removed for inspection of the new bearings; no defects were found. The cam housing hold-down bolt holes were enlarged by 0.031" to permit some side motion.

The engine was given a 6:07 hr endurance run consisting of 4 hrs at 900 hp, 0.5 hr at 1,000 hp, and 1.5 hrs at 900 hp. Oil consumption during this run was 20 to 23 lb/hr at 1,000 hp; the vacuum pump was losing about 4 lb/hr, which should be subtracted from the consumption figures. The engine was removed for inspection, which revealed that the rod bearings had been losing metal from their outer surfaces for some time. The inner surfaces were in good condition. While further service could be obtained from these bearings, they were replaced with the new Allison bearings. The crankshaft center main bearing thrust faces had checked. The other surfaces were acceptable. This bearing was replaced and end clearance increased from 0.003" to 0.006". The piston ring locating pins had been breaking; the broken ones were not replaced. The piston without ring locating pins showed more ring gap increase than the other cylinders' average. XO-1430-1 total time was 280:45 hrs, time above 160 bmep was 21:51 hrs; endurance time was 20:00 hrs, time under power was 189:39 hrs and time motoring was 91:06 hrs.

Contract W-535-AC-9785 – PO 37-4358 – Replacement Parts: Of the 47 contract items, 46 had been completed and accepted. Item #26, accessory housing Dwg #503535, was in work and expected to be complete on 20 May.

PO 37-4716 – Piston Assemblies: New castings from semi-permanent mold equipment were promised by ALCOA on 17 May; if the castings were sound, pistons were to be completed during the following week.

Engineering: Routine drawing changes continued. Layouts to provide a low pressure oil system for the rear accessories and auxiliary high pressure oil line to the front reduction gear bearing were continued. Cambox and cambox cover changes correcting the failures had been laid out. Sketches for a stamped cover were complete. Replacement part lists and Government liability to 15 May 1937 were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 100 – 106.]

20 May 1937. Triggs reported that on 17 May 1937, the XO-1430-1 was run-in 5 hrs for the new connecting rod bearings. During the run a distributor finger, Dwg #503743, cracked in two. Vibration apparently caused the failure as there was no load on the part; it was replaced from stock. On 18 May, a 3-hr endurance run was made at 2,900 rpm and 900 bhp, completing the 5-hr period started on 12 May. The engine stopped once during this run because of carburetor ice. During the last 0.5 hr an oil consumption reading was obtained and a large quantity of coolant was lost. A blow-by increase was noted. Engine operation was satisfactory for the remainder of the 5-hr period. Tear-down inspection revealed that the 1L cylinder barrel had cracked circumferentially inside the water jacket. Continental intended to take the failed parts to MatCmd. These cylinders were the original ones, which had about 160 hrs total time and 20 hrs endurance time. Several single-cylinder engine cylinders had failed after only 20 hrs running. Otherwise, the engine was in good condition and was being reassembled with a new cylinder to run on 21 May 1937. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 108.]

21 May 1937. Tilley and Kinnucan attended a MatCmd conference with Chenoweth and Prescott. Continental exhibited a cylinder barrel, circumferentially-cracked above the second reinforcing flange from the cooling jacket bottom. This crack extended nearly half-way around the cylinder. Continental stated that it knew 0.5 hr prior to shutdown that something was wrong because of the oil dilution with Prestone. However, since the engine operation appeared to be unimpaired, a 5-hr period was completed before shutting down for examination. The cylinder barrel with the crack was left with the MatCmd Materials Branch for detailed examination, although it appeared evident that a design change would be necessary before the trouble could be overcome. MatCmd suggested that a cylinder wall thickness be increased in small increments between the reinforcing flanges, beginning at 0.100" and tapering to 0.156" at the cylinder flange. The corrosion on the cylinder barrel outside, as well as the jacket interior, appeared excessive in view of the fact that both cylinder and jacket had been treated with cadmium prior to assembly. Kinnucan stated that he recalled a number of earlier-design cylinder barrels were not rust-proofed and yet were clean after considerable service. He stated that this mater would be investigated and reported to MatCmd. This might lead to the abandonment of cadmium as a rust coating, especially in view of reports that cadmium increased rather than decreased corrosion.

Prior to 28 May 1937, the engine had 20 hrs endurance running; in a telephone conversation it was learned that an additional 5 hrs had been accomplished ending in another cylinder barrel failure. It was decided during the conference that in the event of another cylinder barrel failure, all 12 cylinders would be replaced using the present cylinder heads and jackets. It was then found feasible to replace the barrels and salvage the jackets by reworking the cylinder head threads, plating the jacket shrink rings, and regrinding to size; since the failure had already occurred, 12 new cylinder barrels incorporating the design change had been put in works. About two weeks would be required to make the 12 cylinder barrels, and an additional two weeks to install them on the engine. He stated that, fortunately, 15 cylinder head forgings were on hand, which would eliminate the extended delay due to the steel mill supply situation. Kinnucan stated that the barrel replacement cost would be approximately $214.50 each, and was requested to supply this information to MatCmd.

During engine operation, several small cracks had appeared at points where stress was concentrated; a stress elimination means was discussed. Regarding the cam housing cover, elimination of the scallops around the stud holes, making the cam cover straight and smooth along its edges, was to be incorporated prior to cam cover replacement. Continental proposed replacing these covers with stamped duralumin covers, but MatCmd discouraged this due to extremely unsatisfactory results with such covers in a previous engine. Several cracks had appeared in the cam housing at points where an abrupt section change occurred. MatCmd proposed using a large radius in the fillets at these points so as to distribute the stress and avoid future failures. Continental expected to have the new cam housings and covers available at the time the new cylinder barrels were installed on the engine.

Continental was experiencing difficulty achieving the correct stretch on connecting rod bolts due to the provision of only one cotter pin hole; Continental proposed to drill two cotter pin hoses at right angles in order to provide 12 cotter-pin locations instead of the present six.

Tilley stated that several left-bank distributor finger failures had occurred. He enquired as to whether the distributor finger failures might be due to temperature conditions; this was dismissed due to completely successful operation on other engines. MatCmd blamed the distributor finger damage on torsional vibration.

Kinnucan stated that incorporating a low-pressure oiling system for the aft accessory case was desirable. Continental requested latest data on the hydro-controlled constant speed propeller governor mechanism so that this feature's design might be undertaken without delay if a type-test engine was required at the conclusion of the 50-hr development test.

Kinnucan questioned whether it was necessary to keep the vacuum pump in operation at all times in view of the difficulty experienced with excessive oil consumption. He stated that MatCmd's instructions for vacuum pump lubrication had been followed to the letter. This matter was referred to the Project Engineer for handling. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 28 May 1937 Memorandum Report E-57-285-62, 116 – 118.]

26 May 1937. Triggs reported that the XO-1430-1 ran 5 hrs on 24 May 1937, 0.5 hr at 3,000 rpm and 1,000 bhp and 4.5 hrs at 2,900 rpm and 900 bhp. During the last 0.75 hrs there was a loss of coolant and decrease in oil consumption. Inspection revealed that the 2L cylinder was cracked similarly to the 1L cylinder that had cracked during the18 May run. The new Allison connecting rod bearings were in poor condition; some showed signs of disintegration and some showed signs of lead segregation. This may have been caused by Prestone in the oil. Enough good bearings were in stock to reassemble the engine. One cylinder was slightly scored, and the piston in this cylinder had no pinned rings. The engine, now with 25 hrs endurance running, was being reassembled for torsiometer and other non-endurance running while new cylinder barrels were made. Further running was expected about 28 May. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 107.]

31 May 1937 Progress Report. No single-cylinder work was done while Continental awaited its base modernization.

The XO-1430-1 was reassembled, replaced on the dynamometer, run-in and an endurance run under contract conditions started. After 3 hrs, coolant started to appear in the blow-by and the oil scale showed a constant weight increase. Ice formed on the throttle disc leading edge; relative humidity was 55%. The engine was inspected and the 1L cylinder barrel was cracked, the connecting rod bearings were spotting on their inner surfaces, and a third right distributor finger failed. New Champion M-11-A plugs were installed. The used plugs were bomb-tested and 75% tested below 150 psi.

The engine was reassembled, returned to the dynamometer, run-in for 7 hrs and removed to inspect the new cylinder, which was in good condition. It was replaced on the dynamometer, run for two hours, and endurance-run under contract conditions for 5 hrs. During the last 0.5 hr there were signs that coolant was being lost into the oil system. The engine was torn down for inspection, which revealed the 2L cylinder barrel was cracked, the connecting rod bearings were breaking down, and three exhaust valves showed gutters on their seats. After a 21 May 1937 Wright Field conference, work began on replacing cylinder barrels with new, heavier-wall barrels. The engine was rebuilt with three new cylinders, three old Bohn connecting rod bearings, two new Allison connecting rod bearings, and one connecting rod bearing not replaced. Exhaust valve seats were re-ground. The engine was returned to the dynamometer with the intent to get more torsiometer data.XO-1430-1 total time was 304:10 hrs, time above 160 bmep was 30:04 hrs, endurance time was 25:32 hrs, time under power was 209:40 hrs, and time motoring was 94:30 hrs.

Contract W-535-AC-9785 – PO 37-4358 – Replacement Parts: All contract items were completed and accepted by the Air Corps Inspector.

PO 37-4716 – Piston Assemblies: These items were now expected to be complete on 8 Jun 1937.

Engineering: The cylinder barrel design was changed to provide more strength where failures had been occurring. A new cam housing was designed that incorporated larger fillets where cracks had appeared in the original housing. The cam housing cover was changed to eliminate the scallops between stud holed; higher bosses were also provided. These changes resulted from a 21 May 1937 Wright Field conference. The revised drawings were to be forwarded to MatCmd for formal approval. A test program was started to evaluate various corrosion prevention methods for stressed metal exposed to ethylene glycol at 250°F. Conferences were held with the National Carbon Company, maker of Prestone anti-freeze, regarding these tests. S.D. Heron of the Ethyl Gasoline Corporation and representing the National Carbon Company, agreed to provide some high-temperature corrosion inhibitors for trial. Replacement part lists and Government liability to 31 May 1937 were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 109 – 115.]

2 Jun 1937. Triggs reported that all new XO-1430-1 cylinder barrels were complete and the old barrels were being removed. Various water jacket corrosion-preventative measures were being tried, including cadmium plating and Lowe Brothers baking enamel. Every effort was being made to complete the cylinders and resume running by 16 June. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 99.]

12 Jun 1937. MatCmd Metallurgist Richard R. Kennedy reported that the Continental XO-1430-1 cylinder barrel, which had cracked after about 20 hrs of testing, had been heat treated to the specified hardness. Microscopic examination revealed the steel had a fine-grained structure but was rather dirty. Fracture examination indicated the failure was due to corrosion fatigue. The cylinder barrel had a Rockwell hardness of B-90, which corresponded to a 235 Brinell hardness. Cylinder barrel structure was shown in Figures 1 – 9.

Cracked Cylinder Barrel

Fig. 1	Fig. 2

Figs. 3 & 4	Figs. 5 & 6	Figs. 7 & 48	Fig. 9

The XO-1430-1 cylinder barrel was forged from SAE 1050 steel. Although engine run time was only 20 hrs the barrel had been assembled for 1.5 years. The barrel had been cadmium plated, assembled in the jacket and its inside diameter ground with steam flowing through the coolant jacket. The cylinder barrel section as received was shown in Figure 1; the circumferential crack extended about half-way around the barrel. Two small holes indicated by arrows extended through the barrel walls The main fatigue crack had its origin in these holes. The fracture surface, shown in Figure 2, was rusty when received but was lightly picked before the photograph was taken.

The corrosion probably started with the steam used to heat the barrel during grinding. The cadmium plate was completely removed by corrosion and the barrel outside rusted. The rust layer was not thick. A section through a fin, as shown in Figure 3, was typical. The surface was rough due to the corrosion and some fairly deep pits were present. The corrosive action was evidently very selective. It was noted that the two holes through the wall were detected along the crack's course. These holes were probably caused by a combination of repeated stress and corrosion. A longitudinal section taken near a hole was examined and was found to contain three small circumferential cracks, two of which appear in Figures 4 and 5. These cracks appear to be enlarged by corrosion. A fine new crack extending beyond the corroded portion of an old crack appears in Figure 6. The steel grain was fine and uniform as shown in Figures 6 through 8. Numerous inclusions were present in the steel, some of which were yellow cubes, possibly zirconium nitride, as shown in Figures 7 and 8, while other consisted of silicates and sulfides as shown in Figure 9. It was possible that the presence of these inclusions influenced the selective corrosion observed in the cylinder barrel. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 12 Jun 1937 Memorandum Report W56-3076, Cylinder Barrel from Continental Engine. 119 – 126.]

10 Jun 1937. Triggs reported that six XO-1430-1 cylinders had been ground and that the balance would be completed by 12 June. The engine was assembled up to the cylinders and was expected to be running again on 15 June. The new modified cam housing castings had been received and were being machined. New cam cover casting has not been received, but were expected, along with the new connecting rod bearings by about 25 June. Four Dwg #503748 right-hand distributor fingers had been broken since running started. Triggs had notified Continental that the Air Corps had been put to considerable expense replacing these parts, yet no action had been taken to remedy the trouble. The matter was referred to the Scintilla Company three weeks prior. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 127.]

15 Jun 1937 Progress Report. No work was done on the single-cylinder engine because the base had not been returned from Wright Field.

The XO-1430-1 with new 2L, 4L and 6L cylinders was run-in for 6 hrs. Since cylinders were being reworked to include revised barrels, the engine was removed from the dynamometer, all cylinders removed and taken apart, and newly-revised barrels assembled to the heads and jackets. The engine was reassembled, but pistons and rings were reused without change; this included a slotted oil ring instead of the standard double bevel scraper ring that had been too severe during cylinder run-in. New, improved distributor fingers replaced the type that had previously failed. All connecting rod bolts had an extra cotter pin hole at 90°to the present one, making it easier to install the cotter pin when the correct bolt stretch was obtained. While waiting for these repairs, the dynamometer setup was modified to have a pressurized coolant system. The expansion tank was raised six feet making pressure at the coolant pump inlet about 5 inHg under maximum flow conditions. The revised setup was to ensure that no air was drawn into the coolant system.

S.D. Heron from the National Carbon Company indicated that air in the ethylene glycol greatly accelerated corrosion. A number of steel samples with protective coatings were subjected to corrosion tests. These samples were placed under stress in a heated ethylene glycol bath at 250°F – 280°F and agitated with an air jet for 41 hrs thus far; some corrosion was already evident. As of 15 Jun 1937 the XO-1430-1 had 310:15 hrs total time, 25:32 hrs endurance time, 30:04 hrs above 160 bmep, 214:20 hrs under power and 95:55 hrs motoring.

PO 37-4716 – Piston Assemblies: These items were complete including inspection. Shipment was delayed pending decision on pattern equipment disposition called for under PO Item #1.

Engineering: Routine drawing changes continued. Layouts investigating relocating spark plugs in cylinder heads to provide better accessibility were in progress. The fits and clearances table for various parts had been completed and was to be forwarded to MatCmd. Layouts providing more oil in the cam box housings, allowing the exhaust valve stems to dip into oil and improve their cooling were being made. This should provide an exhaust valve cooling scheme similar to that used on the single-cylinder engine. New exhaust valve seats with Stellite faces had been made and were to be installed in a new cylinder assembly; flexible exhaust valve seats were also being investigated. Replacement part lists and Government liability to 15 Jun 1937 were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 130 – 135.]

18 Jun 1937. Triggs reported that the new XO-1430-1 cylinder barrels had been run-in for 5 hrs on 16 Jun 1937. The spark plugs repeatedly fouled during most of the run and twice the engine was shut down to clean the plugs. This run was made with purposely high oil consumption to favor the new barrels as much as possible. After 5 hrs the engine became alarmingly rough and was removed from the stand. The accessory drive shaft had seized in the two front bushings and the bushings had been turning in the case. Further inspection revealed four crankcase cracks; the right case had one crack in the recently-strengthened semi-circular rib under cylinder 1. The left case had a crack in each rib under cylinders 1, 2 and 3. No case cracks were observed at the last inspection after 24 hrs endurance running. During the last 5 hrs there was no appreciable load on the engine. No causes for these failures had been determined. Tilley and Kinnucan were taking a case half to MatCmd for discussion. Two rough-machined crankcase castings from the same pattern were available and could be completed in about four weeks. The Scintilla Magneto Company had furnished two new-design distributor finger assemblies, PN 10-12828 and 10-12829, that were expected to eliminate the breakage; these new parts had been installed in the engine. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 136.]

18 – 19 Jun 1937. Tilley and Kinnucan in a visit to Chenoweth and Prescott at Wright Field, and brought with them the left XO-1430-1 crankcase half, in which small cracks had appeared at the longitudinal ribs immediately below the cylinder pads. These cracks were not fully explained, but it was speculated that they may have started during assembly when the main bearing through bolts were tightened to give sufficient crush to the main bearing shells. All agreed that regardless of the cause a crankcase redesign providing additional strength at the failure point would be essential. Continental was tasked to provide MatCmd a sketch showing a double-deck box section modification to provide greatly increased strength at the points where failures had occurred. All concurred agreed that the present crankcase could be used for continued testing provided that the cracks were not too deep to be removed by milling off a small amount of metal from the rib. If the cracks could be removed, engine testing was to continue so as to obtain information on other engine parts. However, no more crankcases were to be constructed until the design modifications had been accomplished.

Kinnucan stated that at some time prior to shutdown the front accessory shaft bearing had seized on the shaft and turned in the reduction gear housing. Some foreign object, a bit rag or wood, had gone through the gears and caused the gear bearing near the failed accessory shaft bearing to move over approximately 0.010". It was apparent that this caused the accessory shaft bushing to stick after which it turned in the aluminum housing.

The new-design crankcase had operated about 25 hrs before the web cracks appeared. Kinnucan stated that the only operational defect was occasional rough running with one or two cylinders missing. However, he did not think the roughness was sufficient to account for the crankcase cracks, nor could the recent rubber mounting on the test stand. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 23 Jun 1937 Memorandum Report E-57-285-63, Conference with Representatives of Continental Motors Corporation on the XO-1430-1 Engine. 128 – 129.]

21 Jun 1937. In a letter to MatCmd following up on a meeting with Prescott, Tilley offered to furnish MatCmd a valve gear assembly for its single-cylinder test engine that was similar to the one Continental had used successfully for the past 2.5 years. This unit featured adjustable valve timing and used the same valve rockers, rollers and bearing caps as used on the XO-1430-1; the cost to MatCmd was $837.24. In a 30 Jun 1937 reply, Lt Col O.P. Echols informed Tilley that in order to expedite MatCmd's test engine completion, MatCmd planned to adapt the old valve gear to the new test engine. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 138 - 139.]

25 Jun 1937. Triggs reported that XO-1430-1 crankcase deflection tests were run with one case half mounted horizontally on a face plate, one cylinder bolted to the case center and weights applied to the cam box mounting studs. Two cases were used, the one that cracked immediately before the latest revision and the latest revision. There was considerable difference in the old and new case deflections, suggesting that strengthening the ribs did some good. However, further engineering would be required to make the crankcase satisfactory. Continental thought the cracked crankcase would stand further running and the engine was being assembled with the intent to run on 28 June. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 137.]

29 Jun 1937. Prescott visited Continental to help explore methods of strengthening the crankcase at the arched ribs extending from one bearing diaphragm to the next, using modeling clay and an old crankcase. Several methods were identified, but it appeared the most feasible was adding a 1.125" wide flange at the longitudinal rib inner edge, but not following the rib outline. The new flange extended straight across the space so as to provide draft in the core box and avoid the use of loose cores that were always troublesome in setting up the mold. Small pockets formed between the cylinder stud bosses were also eliminated for the same reason. There had been no cracks above the cylinder bores to date, but these stud boss pockets were also eliminated. These changes were thought to make the crankcase about 2.5 times stiffer than the present revised crankcase. The added material was distributed so as to maximize the crankcase stiffness and strength, which was hoped to stop further cracks.

New cam boxes and cam covers were also examined to eliminate abrupt section changes at points where small cracks had appeared in the pervious design. It was decided that a very large fillet would distribute the stresses more equally in the casting. Cam box cover cracks had started at the scallop corners; the scallops had been provided to clear the bolt heads. They were completely eliminated and the bolt bosses increased in height so as to provide a very simple cover with no concentrated stress points. It was thought these changes would end cracks in the cam box covers. Continental had also constructed a cam box cover from a simple stamping. Prototypes had been made by hammering duralumin over a hardwood form, which provided a very smooth and workable design that, in production, would be formed by stamping with dies. Continental planned to test the stamped cover on one engine bank and the new cast cover on the other.

Tilley asked about the single-cylinder test engine status and was told that its crankcase had been promised for 30 Jun 1937, after which the engine would be rebuilt and returned to Continental.

The XO-1430-1 had been reassembled to conduct lubricating system tests, along with tests on other engine parts. On the morning of 29 June the engine was run-in and in the afternoon run at rated power and speed; this was the first time Prescott had seen the engine running at full power. Operation appeared to be very smooth except for a peculiar vibration that was quite noticeable; the reduction gear housing front was moving sidewise with considerable amplitude, the engine rear was also vibrating with objectionable amplitude, and a point between cylinders 4 and 5 (the approximate engine/reduction gear center of mass) appeared stationary. This observation led to the conclusion that an imbalance existed, probably in the dynamometer coupling. The individual dynamometer coupling parts had been balanced using parallel bars, but the coupling assembly had never been balanced. The vibration did not appear to be at crankshaft speed, so Continental proposed to investigate the vibration frequency and cause. There was a possibility that this vibration might have contributed to the crankcase and cam box cracks. This vibration was not new, but seemed to have been accentuated by the rubber engine bearer mounts, which permitted freer engine motion than the previous rigid mounts. The vibration was so serious that the carburetor had been removed from the engine, separately mounted on a base, and connected to the supercharger inlet elbow by a flexible duct. Everyone hoped that correcting this vibration would permit the carburetor to be attached directly to the supercharger as originally planned. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 3 Jul 1937 Memorandum Report E-57-285-64, Visit of Mr. F. L. Prescott of the Division to Continental Workers Corp., Detroit, Michigan, June 29, 1937, on the XO-1430-1 Engine. 141 – 143.]

30 Jun 1937 Progress Report. The single-cylinder test engine had not been returned from Wright Field.

The XO-1430-1 was reassembled using cylinders with the new heavy barrels, setup on the dynamometer, run-in for 5.25 hrs to 3,000 rpm and 0 inHgG, and inspected. During this run the engine had periodically been missing due to fouled Champion M-11-B spark plugs that featured both mica and porcelain insulators. See Triggs 18 Jun 1937 report and Prescott's 18 – 19 Jun 1937 report for more details. The right crankcase half was setup for deflection tests; a cylinder was assembled to the crankcase and a 600 lb static load applied to the cylinder's valve end; 550 lb was equivalent to the maximum piston side thrust. Deflection was measured using indicators. Crankcase rib movement was observed to be 0.002"; the original crankcase, with lighter longitudinal ribs, was checked in the same way; its deflection was 0.007".

The engine was reassembled to the dynamometer and run-in for 4 hrs to 3,000 rpm and 1,000 hp. Prescott suggested that the dynamometer coupling might be causing the vibration. After 10 minutes at 1,000 hp the engine was removed, the nose section inspected, and all parts found in good order. The engine was reassembled but further running was delayed while the dynamometer coupling was balanced. As of 30 Jun 1937 the XO-1430-1 had 319:25 hrs total time, 30:24 hrs above 160 bmep, 25:32 hrs endurance time, 221:10 hrs under power and 98.15 hrs motoring.

PO 37-4716 – Piston Assemblies: These parts were accepted and shipped to MatCmd.

Engineering: Layouts had been made showing crankcase longitudinal rub revisions. The pattern equipment was being altered and castings were expected around 8 Jul 1937. Replacement part lists and Government liability were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 144 – 148.]

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