Parts List
(Author's Collection)
Continental XO-1430 Development
Part 5: 1 Jan 1935 to 30 Jun 1935
by Kimble D. McCutcheon
Published 24 Aug 2025; Revised 25 Aug 2025
| During early 1935, a new contract number, W-535-AC-6834, starts to appear in the Continental O-1430 progress reports and other correspondence. It now becomes obvious that Contract W-535-AC-6322, which had covered all prior work, was dedicated to single-cylinder testing, while Contract W-535-AC-6834 was about 12-cylinder engine development. A notable milestone seems to have been achieved during the first half of 1935 – the piston ring/cylinder wall wear problem that had plagued the program from the start disappeared. Unfortunately, if the USAAC and Continental knew why it disappeared, they never said. Numerous material and ring manufacture combinations had been tried, as well as several different lubricants. Perhaps Continental stumbled upon a workable combination but could not document its history. |
| Part 1: Introduction and Background | Part 2: 1932 and 1933 |
| Part 3: 1 Jan 1934 to 30 Jun 1934 | Part 4: 1 Jul 1934 to 31 Dec 1934 |
| Part 5: 1 Jan 1935 to 30 Jun 1935 | Part 6: 1 Jul 1935 to 31 Dec 1935 |
| Part 7: 1 Jan 1936 to 30 Jun 1936 | Part 8: 1 Jul 1936 to 31 Dec 1936 |
| Part 9: 1 Jan 1937 to 30 Jun 1937 | Part 10: 1 Jul 1937 to 31 Dec 1937 |
| Part 11: 1938 | Part 12: 1 Jan 1939 to 30 Jun 1939 |
| Part 13: 1 Jul 1939 to 31 Dec 1939 | Part 14: 1940 and Conclusion |
| Notes to Readers | XO-1430 People | Glossary |
15 Jan 1935. Tilley published a progress report covering the period to date. (NOTE: in the following progress report accounts, unless otherwise stated, Tilley was the author and the reporting period ended on the report date.) Single-cylinder endurance testing had accomplished 50 hrs at 3,300 rpm and 211 imep. A report had been compiled and submitted separately, together for a request for release of the Contract W-535-AC-6322 balance. A new head and barrel were in work for further single-cylinder testing. The barrel would have a hardness equal to those used in the successful tests at 3,000 rpm and 211 imep previously reported. This assembly was to be complete by 26 Jan 1935. There was no change in the drawing status.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 5 – 6.]
1 Feb 1935 Progress Report. While awaiting a new cylinder, the test engine was inspected, the connecting rod bearing and bushing replaced, and the flywheel hub and oil seal cover plate were modified to accept a spring-loaded leather oil seal. The new cylinder was assembled with the Lo-Ex piston described in the last 50-hr report, with a Gold Seal ring in the top groove and American Hammered rings with inner rings in the remaining grooves. The cylinder was run-in on 31 Jan 1935 up to 1 inHgG boost when operation became faulty. The piston crown was eroded away, so a Y-alloy piston was being reground to continue the run. A stock list was being made that would conform to Contract Nos. W-535-AC-6322 and W-535-AC-6834 Items for shop releases when authorized. Continental awaited a MatCmd decision about changing the propeller shaft end and nose plate to the proposed new standard. [USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 8 – 9.]
15 Feb 1935 Progress Report for Contract Nos. W-535-AC-6322 and W-535-AC-6834. Piston No. 25 was reground to suit the 5.495" cylinder bore. A Gold Seal ring was placed in the top groove and three American Hammered rings with expanders were placed in the others. After run-in to 10 inHgG boost at 3,000 rpm, cylinder wear at the ring travel head end was 0.0045"; after run-in to 18 inHgG boost this wear increased to 0.006". Another Gold Seal ring was placed in the second groove, and the top and forth grooves were left empty, leaving two rings total; blow-by increased from 20 ft³/hr to 46 ft³/hr and wear continued at the ring travel extremes.
The cylinder was reground and honed to 5.5015" diameter. A new Y-alloy piston (No. 27) was made for three 0.094" rings with an oil drain bevel below the third ring. A heat dam (empty groove to reduce heat flow from the piston crown to the ring below) similar to the one used in the first 50-hr Hyper No. 2A cylinder test was cut into the top land. Cylinder wall clearances were reduced 0.024" at the skirt top. Three American Hammered compression rings without inner rings were installed. After a 6-hr run-in to 3,000 rpm and 0 inHgG boost, the ring gaps had increased from 0.002" to 0.004" but there was no cylinder wear. The run-in was continued to 3,000 rpm and 10 inHgG boost and the ring gaps increased to 0.004" to 0.006", still with no cylinder wear. After run-in to 3,000 rpm and 211 imep there was no further ring or cylinder wear.
The stock list drawings arranged per items of the subject contracts was completed and shop releases were being made when authorized. A part weight analysis based on the detail drawings had been started. A review and completion of engineering calculations of all parts had been started. In his 20 Feb 1935 transmittal letter for this report, Tilley noted that after 15 Feb 1935, short runs at 3,000 to 3,300 rpm and 211 imep had been accomplished without appreciable ring or cylinder bore wear. A 5-hr run under contract conditions was being started on 20 February.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 10 – 12.]
1 Mar 1935 Progress Report. The compression ratio had been measured at 5.85:1. After a 2-hr run-in, a further 1-hr run at 3,000 rpm and 211 imep caused no piston ring or cylinder bore wear. The engine was run for 2:50 hrs at 3,300 rpm at from 0 boost to the boost required to obtain 211 imep to determine the blow-by versus intake pressure. The blow-by varied irregularly from 17 to 30 ft³/hr. The general trend was blow-by increase with boost increase, especially above 15 inHgG. After another 45 min at 3,300 rpm and 211 imep, the heat dam groove was filled with carbon on its intake side. This carbon was removed. Rings and cylinder bore were in good condition. After 30 min more at 3,300 rpm and 211 imep excessive blow-by resulted in the test being stopped. The second ring was broken, the lands adjacent to the heat dam had eroded in the piston's intake side, and their edges were rounded. The top piston crown edge was not eroded.
The piston was cleaned and new rings placed in all grooves. After running in to 3,000 rpm and 0 inHgG boost and inspection revealed the moving surfaces were OK, run-in continued to 18 inHgG boost and then an endurance run began at 3,300 rpm and 211 imep. After 3:30 hrs the run was stopped due to excessive blow-by. The piston was excessively eroded on its intake side, the second ring gap had increased by 0.023" while the top ring gap had only increased by 0.003" and the third 0.009".
A new piston (No. 28) was machined with more top land and less heat dam groove volume, and a 0.125" second-ring groove. The cylinder was honed to 5.504" diameter. Following a 5-hr run-in, no defects were observed; the cylinder was reassembled and the run-in continued.
Engineering: Shop releases had been made of authorized items; review and compilation of engineering calculations continued. The front crankcase, thrust bearing retainer and cover drawings were being revised to incorporate the new controllable-pitch propeller standard.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 14 – 15.]
15 Mar 1935 Progress Report. The run-in was continued to 9 inHgG boost when blow-by increased; the ring gaps had increased by 0.007" and cylinder bore was streaked by aluminum pick-up. The bore was smoothed with emery cloth and the rings replaced by new ones, which were run-in to 3,000 rpm and 211 imep, and then an additional 1 hr. Inspection showed that tool marks were still visible on the rings.
After 1 hr at 3,300 rpm and 211 imep inspection showed that neither the rings nor cylinder bore was wearing. After 2:20 hrs total at 3,300 rpm and 211 imep, blow-by became excessive; the top ring gap had increased by 0.011" and the second by 0.005". The second groove was re-machined to 0.188" wide and two 0.094" rings placed in it; the other rings were replaced by new ones. The cylinder was run-in and then tested for 1 hr at 3,000 rpm and 211 imep without showing wear. After another 40 min at 3,300 rpm and 211 imep, blow-by became excessive and a crack appeared in the cylinder head jacket near a spark plug; ring gaps were within 20° of one another and the crack was patched.
The cylinder was run at 3,300 rpm and 211 imep for 53 min when blow-by became excessive. The third ring was broken about 0.75" from the gap and the other ring gaps had increased by 0.002" to 0.004" and were nearly in line. The cylinder bore was lapped with grinding compound, an anti-rotation pin placed in each groove, and new American Hammered rings installed. After run-in to 3,000 rpm and 3 inHgG, inspection revealed that the pin in the second groove was broken; a larger pin was placed in the second groove and the run-in continued.
The cylinder used in the last 50-hr test was reground with the jacket heated to 250°F. When cold, this bore was stepped so that the diameters were as follows: skirt = 5.542"; under jacket = 5.539"; under thread = 5.535". A piston was being machined to give the same clearances, ring location, etc., as the one on test, based on the diameter under jacket. The test engine coolant pump packing required frequent attention because the bearings did not adequately locate the pump shaft.
Orders were placed for reduction gear housing, crankcase and accessory drive housing pattern construction. Orders were being placed for crankshaft and connecting rod dies and forgings, as well as camshaft housing, camshaft housing covers and intake manifold patterns and castings. Inquiries were being made for reduction gears, supercharger, carburetor, ignition distributors and connecting rod bearings.
Engineering: Review and compilation of engineering calculations continued. Front reduction gear housing, thrust bearing retainer, and cover drawing revisions were complete, and study of coolant pump seals had been initiated.
In his 26 Mar 1935 progress report transmittal letter, Tilley stated that since the report was released a cylinder had run 26 hrs without apparent wear; a report was being prepared.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 16 – 19.]
30 Mar 1935. Prescott issued Memorandum Report E-57-285-13 about a 6 Mar 1935 conference at MatCmd between Continental's Kinnucan and Morehouse, and Prescott on the XO-1430-1 engine. Firing order for opposed and vee-type 12-cylinder engines, with optional rotation direction were discussed. Continental had apparently misunderstood MatCmd's request to use the same fuel injector on both opposed and vee engines, thinking it was also implied that the same firing orders should be used in either case. This was impractical because even with the same bank firing order, in one case the bank phase difference would be 180° and 60° for the other. The intention was to use one 12-cylinder injector for either engine although the injector pumps would not serve the same cylinders.
Single-cylinder test engine piston and ring setup was discussed. The later attempts included a heat dam above the top ring, 0.094" rings, with two in the middle groove and one above and below the double-width groove. No extremely encouraging results were obtained. The question of oil quality was discussed and Prescott suggested that castor oil be tried in an effort to determine whether the oil was responsible for ring wear. MatCmd had also recently experienced ring wear difficulty, and was trying castor oil as a remedy, postulating that regular oil may have lost its ability to maintain a film due to some change in the refining procedure. MatCmd first thought this difficulty was peculiar to high-speed engines, but airlines had reported trouble in radial engines with no change in operating conditions. Rings had the appearance of running dry, and excessive blow-by accompanied the ring-wear condition, indicating the lack of oil sealing and lubricating film loss. If the oil characteristic that allowed it to re-form a film after the rings passed over the cylinder wall were reduced during production using a new process, castor oil use should restore normal ring life and identify a plan for problem solution.
Continental requested a new blueprint of Steel Products Engineering Company Dwg No. 97, High Speed Single Cylinder Test Engine Assembly, because the existing print had been worn out; MatCmd agreed to furnish this.
The point was raised that the gun synchronizer cam had two lobes, yet the planned propeller had three blades. The cam speed equaled the propeller speed, meaning that either one or three lobes would be required. The Armament Branch was contacted and recommended a single-lobe cam.
|
| Single-Cylinder Parts List (Author's Collection) |
Continental asked if action had been taken on the single-cylinder tests it had proposed in a 30 Jan 1935 letter, which included a connecting rod, rocker arms, valves, springs, etc., exactly as planned for the 12-cylinder engine. Since this would involve additional funds, MatCmd deferred action on this until the single-cylinder tests showed more progress.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 24 – 25.]
31 Mar 1935 Progress Report. The engine ran 26 hrs endurance at 3,300 rpm and 211 imep with no cylinder bore wear and negligible ring wear. A report on this testing was submitted. The test engine was inspected. Bevel gear PN I52 had a broken tooth. A gear from the other side was put in its place and a new gear was to be made as soon as the drawing requested on 26 March was received. The coolant pump was being repaired, the camshaft housing bushed to repair the bearing and journal wear adjacent to the cams. The cylinder was ground hot and would be used for performance tests with and indicator, reference valve timing, intake pipe sizes, etc. The effect of differential coolant flow was to be investigated.
Continental had authorized pattern modifications and construction of a test cylinder, connecting rod, etc., for cylinder tests; the cylinder, valve gear, piston, and connecting rod were practically identical to those planned for the 12-cylinder engine. Continental requested MatCmd authorization to modify the test engine parts as shown in Continental Dwg Hyper 603 submitted earlier. A report on testing with internally-cooled pistons was in process.
Continental set a completion date of 15 Jul 1935 for the parts authorized for Contract W-535-AC-6322 Items 2 and 3, and Contract W-535-AC-6834 Items 1, 2, 3 and 4. Crankcase, reduction gear and accessory drive housing castings were promised for 20 Apr 1935. An order for a crankshaft forging had been placed, but no delivery promise was available. Requisitions for standard and duplicate finished parts had been made. Inquiries were out for rod forgings, cam housing, camshaft and intake manifold. Total estimated labor hours released to shop was 180.
The review and compilation of engineering calculations for all parts continued, as did the weight estimate of all parts from detailed drawings. Revision of several details to obtain weight reduction had been started.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 21 – 23.]
15 Apr 1935 Progress Report. A new coolant pump shaft was installed using only one top bearing instead of two. The Prescott indicator was connected to the cylinder but no indicator cards were obtained due to sluggish action; the sampling valve was being reworked. The Farnborough indicator was connected, but no cards were obtained.
Cylinder coolant connections were changed so that the coolant entered the transfer elbow on the intake side and left through the exhaust side. A small vent was placed at the exhaust port outlet (former outlet connection). During a 1-hr run at 3,000 rpm and 211 imep, thermocouples placed at inlets and outlets indicated no great difference from previous runs, except the vent was 20°F higher than the main outlet.
The report on tests with internally-cooled pistons was completed and submitted to MatCmd. The pistons used in the tests were being examined internally and externally by the Wilcox Rich Corporation. A report covering this examination was to be sent when available.
The cylinder head pattern was being modified to conform to 12-cylinder requirements except for the exhaust port coolant outlet, which was to be changed after castings were obtained for further single-cylinder tests.
The weight estimate for each part was to be completed prior to the next progress report. Numerous minor drawing changes had been made as a result of starting procurement and manufacture of parts. These changes were to be reviewed by the Air Corps Inspector during his weekly visits for process inspection. Those not approved or out of the inspector's jurisdiction were to be forwarded to MatCmd for necessary action. Detailing test engine parts per layout Dwg 603 had been started. Compilation of engineering calculations continued.
Parts held up included the mounting plate assemblies, and the coolant pump assembly, which was waiting for a better pump shaft packing.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 27 – 29.]
23 Apr 1935. Prescott issued Memorandum Report E-57-285-14 describing a 16 Apr 1935 XO-1430-1 engine conference that included Long, Vincent and Tilley of Continental and PPL's Maj Powers and PPL civilian engineers Chenoweth, Lake and Prescott. Continental stated that in more than 1,000 labor hours on XO-1430-1 parts had been released to its shops. MatCmd wanted an Air Corps Inspector to follow the work at least one day per week, and more if required as work progressed. Lake stated that Charles Bond, now at Marvel Carburetor Company, Flint, Michigan, would be issued orders to visit Continental during the week of 22 Apr 1935, and at frequent intervals thereafter. MatCmd did not intend to relieve Continental of inspection duties, but to follow its inspections, and where finished parts came up to Government standards, accept and stamp them. Such parts were then to be placed in safe keeping until engine assembly was started.
[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 30 – 32.]
30 Apr 1935 Progress Report. Farnborough indicator cards at 3,000 and 3,300 rpm and 211 imep were used to check the results of previous cards for investigation of crankshaft torsional resonance. It appeared that more valve opening overlap or earlier exhaust opening at exhaust dead center may improve performance. The coolant flow was changed to enter from the cylinder exhaust side and leave from the intake port side. No marked operational difference was observed. The coolant temperature rise appeared to be less with the cross flow than with flow from the jacket bottom to exhaust port top.
After 3 hrs operation at rated output during the foregoing tests, the piston seized. The cylinder bore was out-of-round by 0.008". Piston examination showed that the second piston ring had overridden its locating pin, which jammed the ring against the cylinder bore, causing the failure. The cylinder with the long jacket whose bore was ground a 250°F was assembled to the test engine. The new piston had the same piston ring arrangement as used in the 25-hr endurance run. After run-in to 3,000 rpm and no supercharge, the second piston ring locating pin was found broken, which resulted in cylinder wall scratches. The piston ring locating pins in the second groove were replaced with 0.125" diameter pins and the cylinder wall was lapped. Run-in was continued up to 18 inHgG boost at 3,000 rpm and 10 bmep, more than the previous cylinder had attained.
Crankcase, reduction gear, rear accessory and cam housing castings were promised for 10 May 1935. The crankshaft forging was promised for 19 May 1935. Reduction gears were promised for 5 Jun 1935. The supercharger order was not yet accepted by GE, awaiting conference with Dr. Moss, scheduled for 7 May. Contract W-535-AC-6834 Items 5 and 6 were released to shop planning, which was making shop orders for material and work.
Engineering: A weight estimate from detail drawings and complete parts list had been completed. The total was 1,160 lb, or 40 lb above contract requirements. Of this increase, 6.5 lb was attributed to the inclusion of hydraulic propeller control and a standardized engine nose adaptable to controllable propeller. A 9 lb weight increase was attributed to pistons, and the balance was due to an increase in cylinder assembly weight. Detail drawings and stock lists for single-cylinder setup to test connecting rods and valve gear were identical to those of the 12-cylinder engine were nearly complete. Minor drawing O-1430-1 engine drawing changes had been reviewed by the Air Corps Inspector and OK'd except cylinder barrel, jacket and piston drawings, which had been sent to MatCmd for approval.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 34 – 37.]
1 May 1935. Continental Design Engineer James W. Kinnucan published Design Report No. 63, Continental O-1430-1 Engine Weight Estimate from Detail Drawings, the purpose of which was to accurately determine the engine weight as detailed. Each detail drawing listed on the Air Corps stock list was examined and the part's weight calculated. Table P501 summarizes these results. Table P502 compares two previous estimates and this calculation. The calculated engine weight totaled 1,158.9 lb, which included a 24-lb allowance for a carburetor, the details of which were not available. The gun synchronizers were not included, but its mounting pad cover plate was. The mounting plate assembly (engine mount) was omitted. While the actual weight was expected to vary slightly from that calculated, the slight errors usually balanced themselves. However, the 1,159 lb weight did not meet the contract requirement.
| Assembly | Estimated Weight (lb) |
|---|---|
| Crankcase Assy Part List Number (hereinafter PL) 43886 – 43888 | 146.6 |
| Crankshaft Assy PL 43889 | 88.5 |
| Accessory Drive Shaft Assy PL 43890 | 7.9 |
| Reduction Gear Assy PL 43891 – 43896 | 165.7 |
| Accessory Drive Housing Assy PL 43897 – 43901 | 32.4 |
| Coolant Pump Assy PL 43902 – 43903 | 6.7 |
| Oil Pump Assy PL 43904 | 5.3 |
| Connecting Rod Assy (Fork) PL 43905 | 35.6 |
| Connecting Rod Assy (Blade) PL 43906 | 18.9 |
| Piston Assy PL 43907 | 70.3 |
| Cylinder Assy PL 439080 – 43909 | 308.1 |
| Camshaft Housing Assy PL 43910 – 43911 | 64.3 |
| Valve Rocker Assy PL 43912 – 43913 | 24.6 |
| Camshaft Drive Assy PL 43914 | 7.0 |
| Camshaft Accessory Drive Housing Assy PL 43915 – 43916 | 5.3 |
| Gun Synchronizer Assy1 PL 43917 – 43920 | 1.0 |
| Induction System PL 43921 – 43923 | 71.6 |
| Ignition System PL 43924 – 43925 | 39.8 |
| Miscellaneous additional main assy small parts2 as called for by PL 43880 – 43885 | 59.3 |
| TOTAL ENGINE WEIGHT | 1,158.9 |
| Notes: 1. All gun synchronizer parts omitted and a special cover substituted. The omitted parts weighed 6.0 lb. 2. Part No. 503786 Mounting Plate Assy omitted. | |
| Assembly | Original Estimate (lb) | 16 Jan 1934 Estimate (lb) | 1 May 1935 Estimate (lb) |
|---|---|---|---|
| Crankshaft | 93 | 93 | 89 |
| Crankcase (Main) | 189 | 209 | 156 |
| Reduction Gears, Front Crankcase | 115 | 114 | 165 |
| Front Accessory Drive | 10 | 11 | 11 |
| Camshaft | 101 | 90 | 90 |
| Camshaft Drive | 8 | 8 | 7 |
| Camshaft Accessory Drive | 10 | 13 | 6 |
| Cylinder | 272 | 269 | 312 |
| Piston | 65 | 61 | 70 |
| Connecting Rods | 56 | 55 | 54 |
| Supercharger | 25 | 18 | 20 |
| Oil Pump and Cleaner | 10 | 10 | 9 |
| Coolant Pump | 10 | 6 | 7 |
| Coolant Manifold and Fittings | 16 | 14 | 15 |
| Rear Crankcase and Accessory Drive | 29 | 24 | 33 |
| Ignition System (Breeze) | 48 | 48 | 40 |
| Carburetor and Air Intake | 26 | 26 | 26 |
| Intake Manifold and Pipes | 27 | 27 | 28 |
| Propeller Attaching Parts | 3 | 5 | 6 |
| Miscellaneous | 7 | 5 | 14 |
| TOTALS | 1120 | 1106 | 1158 |
[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 38 – 41.]
15 May 1935 Progress Report. After several efforts to eliminate faulty cards obtained with the Prescott indicator, the Farnborough indicator was set up. Timing changes were then tried at 3,000 and 3,300 rpm, 18 inHgG boost. The following results were obtained, the timing figures are comparative, tappet clearance was 0.100" and speed was 3,000 rpm; friction runs were made after each power run.
| Timing Tag | Intake Open | Exhaust Open | Intake Close | Exhaust Close | imep |
|---|---|---|---|---|---|
| 1* | 2 BTC | 40 BBC | 39 ABC | 1 ATC | 213 |
| 2 | 3 BTC | 50 BBC | 37 ABC | 8 ATC | 210 |
| 3 | 12 BTC | 40 BBC | 29 ABC | 1 ATC | 205 |
| 5 | 7 ATC | 39 BBC | 49 ABC | 2 ATC | 215 |
| 6 | 3 BTC | 33 BBC | 38 ABC | 9 ATC | 218 |
| 7 | 9 ATC | 30 BBC | 49 ABC | 11 ATC | 222 |
| * Used for endurance tests | |||||
The engine ran 5.5 hrs at 18 inHgG boost at or above 3,000 rpm for these tests. This same cylinder was used for the 50-hr endurance run at 3,300 rpm reported on 8 Jan 1935. Its total time at 211 imep was about 61 hrs. The piston/ring arrangement was the same as for the 25-hr test reported 25 Mar 1935. No cylinder bore or ring wear had been observed. Coolant flow has been across the cylinder with the exhaust port outlet serving as a vent only. Tests with different valve spring weights to obtain mep versus rpm continued. New single-cylinder test engine parts had been released for manufacture. Cambox and cylinder head castings had been received and were being machined. Other material was being procured. Test engine parts modification was not to be started without MatCmd authorization.
[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 43 – 46.]
31 May 1935 Progress Report. Valve spring tests to determine the load required by several valve spring combinations produced the following results:
| Clatter Speed (rpm) | Spring Load (lb) | |
|---|---|---|
| Closed | Open | |
| Over 3,300 | 159 | 180 |
| Over 3,300 | 110 | 192 |
| Over 3,300 | 90 | 158 |
| 3,120 | 65 | 128 |
| 3,160 | 72 | 134 |
In each case the boost was 20 inHgG. With no boost the clatter speed was 20 rpm higher than the above values. No detrimental effect on power at 3,300 rpm was observed with the last spring combination. A spring-loaded clearance take-up, with vernier scales, was placed on tappet adjustment, which projected above a special cambox cover, modified to prevent oil splash. With the cold clearances set at 0.015", observations were made of running clearances at the valve tips for various operating conditions as follows:
| Intake Clearance | Exhaust Clearance | Engine Condition |
|---|---|---|
| 0.015" | 0.015" | Cold friction, 500 rpm |
| 0.024" | 0.010" | 0 Boost, 2,300 rpm |
| 0.025" | 0.010" | 15 inHgG boost, 2,300 rpm |
| 0.025" | 0.021" | Hot friction, 2,300 rpm |
The vernier was easiest to read at 2,300 rpm. Observations at 3,000 rpm were planned.
Test engine inspection after these tests showed the upper locating pin in the second piston ring groove to be broken and the lower one loose. Bearing was at the pin's outer edge. New pins were to be fitted so that they bore at the ring root to decrease bending moment on the pins. Total time at 211 imep or better for this cylinder was 62.25 hrs of which 0.75 hrs was at 2,300 rpm.
Single-cylinder parts in work included cylinder heads, cambox, adapter, camshaft, connecting rods, pistons, and balancing rods. Some small parts, such as gaskets, intake pipe valve seat inserts, and washers were complete. Because of waiting on material that was to be used in the 12-cylinder, there was delay in completing all single-cylinder parts, but all material was expected by 15 Jun 1935 and the single-cylinder parts were expected to be complete by 1 Jul 1935. Modification of the present test engine was planned after the bmep versus rpm tests were complete, which was scheduled for week of June 3) and MatCmd's authorization.
Engineering: Single-cylinder coolant pump revision was complete. The same changes were studied for the 12-cylinder engine; the new seal can be accommodated by design revision requiring new parts but using the same pattern equipment. Mounting plate detail for test purposes was nearly complete; Continental proposed that it be substituted for the ship mount submitted with drawings. Valve spring analysis was covered by Design Report No. 63 (NOTE: This report was differt from the Design Report No. 63, which provided the weight estimate, but for some reason was assigned a duplicate report number). A review of details has been started, the object of which was to reduce weight, simplify the design and improve reliability. The carburetor air screen for downdraught carburetors was redesigned and released to the shop. Coordination with foundry and machine shop, judging inspection results for pattern equipment correction, authorization of deviations, drawing changes, etc., occupies a considerable portion of the engineering department's time.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 48 – 51.]
6 Jun 1935. Kinnucan published Design Report No. 63, Continental O-1430-1 Engine: Minimum Weight Valve Springs.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 52 – 61.]
15 Jun 1935 Progress Report. A trial to determine single-cylinder hot valve clearances at 3,000 rpm with a stiffer spring in the vernier permitted observations up to 3 inHgG boost. These values matched those previously reported for 2,300 rpm. Above 3 inHgG boost cylinder vibration blurred the vernier preventing close observation. Tests to obtain performance data – mep versus boost and rpm – were started using 160°F intake air in order to compare directly with original data on the Hyper No. 2 cylinder. Total time ≥211 imep for this cylinder was 62.5 hrs. All single-cylinder part material had been received, and all parts were in work except test engine parts that required modification. Assembly of heads, barrels and jackets was to be done during the week of 24 June. All parts were expected to be complete by 5 July.
Engineering: Mount plate details for test purposes were complete. Changes required to facilitate molding and procurement of castings were made on several drawings. Routine changes clarifying or completing shop drawings had been made. Crankshaft bearing load diagrams were revised to conform to final detail drawings. The crankshaft mass moment of inertia was recalculated from current detail drawings. [USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 63 – 66.]
26 Jun 1935. Prescott penned Memorandum Report E-57-285-14 confirming a conference at MatCmd on 15 Jun 1935 between Kinnucan and Prescott. Kinnucan stated that much contract-engine material was on hand and many parts were finished; forgings and castings were causing delays. The grain flow in the crankshaft forgings was excellent and the shaft was being machined. It was necessary to reject the crankcase castings because of heavy and non-uniform sections, but new castings were in work in the machine shop and would be completed soon. Work on the single-cylinder engine was held up until the PPL representative's visit on 26 Jun 1935. It was planned to then modify the crankshaft as required to adapt the engine for 12-cylinder connecting rod tests.
Mount plate details for dynamometer testing were discussed and it was agreed that for this purpose a different mount plate adapted for installation on wood sills would be preferable for dynamometer work, while for torque stand operation the aircraft type mount plate would be fitted. A straight-plate design, either with angles riveted to the upper and lower edges, or with edges formed by bending on approximately the same radius used for the tapered aircraft mount, was to be drawn up an submitted for formal release for dynamometer operation only.
The crankcase nose section required slight modification to eliminate sharp corners and blind pockets that could not be properly inspected.
The cylinder bores were to be taper-ground so that it very closely approached a true cylinder when hot. Kinnucan stated that no further piston or ring difficulties were being experienced since the ring pin diameter had been increased. Continental was proceeding with single-cylinder testing on its own initiative without waiting for receipt of formal authorization, as soon as the necessary single-cylinder changes were released by MatCmd.
Kinnucan stated that a new valve spring set had been designed on the principle of least weight for a given amount of work (see Design Report No. 63). These springs saved about 12 lb on the 12-cylinder engine and were to be included in the single-cylinder test program. Other springs, designed as these, had proven successful on automobile engines and Continental thought it worthwhile to give them a thorough test.
Crankshaft torsional resonances were discussed and Prescott observed that 2nd node vibration was serious enough in high-speed, high-output engine using soft quill drives to warrant analytical investigation into steps for reducing the amplitude of such vibration. Continental was to report the results of this investigation to MatCmd.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 67 – 68.]
30 Jun 1935 Progress Report. The same piston with new American Hammered rings was installed in the long-jacket cylinder and run-in. Previous runs had been showing erratic high blow-by whose only explanation was that one of the ring pins became loose. A series of power readings were taken from 0 to 18 inHgG boost over a 2,000 to 3,300 rpm speed range. One set of readings was taken by holding the engine speed constant and varying the carburetor intake pressure; another reading set held the carburetor intake pressure constant and varying the engine speed. Inconsistencies appeared when the two data sets were plotted and compared, suggesting the data needed to be checked. A preliminary report covering these tests was planned.
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| Prescott Indicator Patent |
Ford Prescott checked Continental's use of the Prescott indicator and diagnosed a leaky valve and poorly proportioned oil reservoir; both were replaced. Cards were taken for comparison to cards taken by the Farnborough indicator. While a comparison was not available for this report, a preliminary report was planned.
The test engine was disassembled to modify the crankshaft and other parts so the 12-cylinder connecting rod design could be tested. One of the two new cylinders had been assembled and Continental expected the Air Corps Inspector could review enough material during the week of 8 July to permit test engine assembly during the week of 15 July.
Contract W-535-AC-6322, Item 2 – Crankcase. Front and rear reduction gear housings were again rejected. New castings were promised for 11 July. The main crankcase awaited studs and bolts for fastening the halves together before boring the main bearing bosses
Contract W-535-AC-6322, Item 3 – Crankshaft. Finish-machining, including dynamic balancing was expected on 18 July. The crankshaft was being magnafluxed by the Ohio Crankshaft Company. Other related parts were complete except for the reduction gear quill drive adapter.
W-535-AC-6834, Item 1 – Reduction Gears. All parts had been received and inspected. Three reduction gears were rejected by the Air Corps Inspector due to imperfections on the tooth faces and outside diameter dimensions being too small. The Farrell-Birmingham Company foreman charged with making these gears, in conference with the Air Corps Inspector and Continental engineers, stated that the Farrell-Birmingham Company would guarantee these gears despite the discrepancies noticed. He also explained how each mark occurred. These gears were sent to the MatCmd Inspection Branch at Wright Field to be magnafluxed. If no cracks were indicated, as the gear company was confident would be the case, other imperfections on the outside diameters were to be removed by stoning and a deviation requested.
W-535-AC-6834, Item 2 – Rear Accessory Housing Assembly. All material had been received except the supercharger, which was promised for 18 July. Several Belgrim bevel gears required re-cutting. The corrected housing casting had been received and was in work. The completion date for the assembly would be available in the next progress report.
W-535-AC-6834, Item 3 – Camshaft Housing Assembly. The housing pattern had been corrected, a sample casting received, checked and released for manufacture; a duplicate casting was on order. All other material was on hand or in work except for the distributor housing castings, which were rejected and whose pattern was being corrected. Rocker arm completion awaited single-cylinder tests.
W-535-AC-6834, Item 4 – Connecting Rod Assemblies. Forgings had been received but machining awaited single-cylinder tests.
W-535-AC-6834, Item 5 – Cylinder Assemblies. A sample head casting had been received and approved, and the other castings had been ordered. All other parts were in work or awaiting inspection. A completion date estimate would be available for the next progress report.
W-535-AC-6834, Item 6 – Piston Assembly and other items to complete the engine. Piston castings had been received but machining was delayed until single-cylinder work was complete. Other items were work or in storage.
Engineering: Routine drawing changes to clarify or expand instructions continued. The single-cylinder test engine dynamic balance had been checked using actual weights of the various new connecting rods, pistons and balancing rods. The crankshaft balance load diagram was being revised to conform to detail drawings. An error in the crankshaft dynamic balance had been discovered and corrective instructions given to the Ohio Crankshaft Company, which was machining this part. These instructions described the unbalance correction method as shown on the dynamic balancing machine. This error would have been discovered when Continental tried this crankshaft on its own dynamic balancing machine. A study to determine the propeller/crankshaft system second-mode torsional vibration characteristics had been started. A special rolling fixture for checking reduction gear tooth errors had been designed and construction started.Item[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 73 – 77.]
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