Continental XO-1430 Development
Part 3: 1 Jan 1934 to 30 Jun 1934
by Kimble D. McCutcheon
Published 13 Aug 2025; Revised 8 Sep 2025

25 Jan 1934. PPL civilian engineer Ford L. Prescott released Memorandum Report E-57-341-1 relating a conference held on 18 Jan 1934 with W.E. Sykes of Farrel-Birmingham Co. (a gear and gear-making machinery company) and Continental's Tilley and Furay. The question was raised as to the necessity of holding to exact gear ratios, and it was decided that this was unnecessary in view of the benefits in longer life that were obtained when the gear tooth were incommensurate or a "Hunting Tooth" was employed in each pair. On the question of gear loading and life, it was decided that the gearing should show no appreciable wear after 1,500 to 1,000 hrs at 87% speed and 67% power, but that some gear wear would be permissible in 150 hrs full throttle operation. This enabled loading the gears to a greater degree, thus saving unnecessary weight.

Sykes explained the desirability of Sykes gears for gear pumps and stated that he wished to incorporate his gears in a pump adapted for fuel or oil pumping. He was instructed to write the Division for a copy of the fuel pump specification. Sykes stated that he had made large numbers of oil pumps for pressures of 1,000 psi or more, and such pumps did not give a pulsating flow, nor did they require relieving the end plates to eliminate fluid hammer due to pocketing fluid between engaging gear teeth. The suction lift properties of Sykes gears were stated to be much superior to spur gears.

The necessity of securing some information on gear life under various loads was discussed and it was decided to investigate the feasibility of testing two GIV-1570 reduction gears by applying a torque between them in such a manner that each gear pair loaded the other and the only power required was used to overcome friction losses. It was stated that a brief study would be made to determine the cost of such a test. It was pointed out that this matter was of extreme importance, in view of the fact that the crankcase design to be furnished to the Government was affected by reduction gearing design.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 14 – 15.]

10 Feb 1934. Prescott released Memorandum Report E-57-126-1 documenting a conference with Mr. Welty of the Aluminum Company of America (ALCOA) and Continental's Tilley, which was held at MatCmd on 1 Feb 1934. Welty explained the difficulty in securing the physical properties called for on the cylinder head drawing and showed that these physical properties were lost when the heads were shrunk onto the barrels. He stated that better final physical properties could be obtained if the casting heat treatment was revised, and planned to write MatCmd a letter to that effect. Prescott recommended to Continental that the drawing specification be revised after receipt of Welty's letter.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 16.]

[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 17 – 18.]

6 Mar 1934. Continental Design Engineer James. W. Kinnucan released Design Report No. 51, Continental O-1430-1 Engine: Stress Analysis of Connecting Rods.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 27 – 34.]; Design Report No. 52, Continental O-1430-1 Engine: Stress in Teeth of Reduction Gear.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 35 – 36.]; Design Report No. 53, Continental O-1430-1 Engine: Piston Velocity, Acceleration and Side Thrust.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 37 – 42.] and Design Report No. 54, Continental O-1430-1 Engine: Valve Timing, Opening Areas, Velocity, Acceleration and Force Due to Acceleration .[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 45 – 54.].

20 Mar 1934. Continental Chief Engineer N.N. Tilley submitted a progress report for the period ending 15 Mar 1934. Further work had been required to make the new test setup operate. The test cylinder was run in by motoring up to 1,500 rpm for 5 hrs and under power up to 2,500 rpm without supercharging for 7 hrs. No accurate power determination had been done. Exhaust valve clearance had not changed, indicating freedom from valve seat recession. The cylinder was removed for inspection and found satisfactory. Both valves were gasoline tight. The cylinder was reassembled and testing resumed. The Prescott indicator was set up and tried, but no successful indicator cards were obtained. Steel piston rings had been promised for 20 Mar 1934 and were desired prior to the first 50-hr run. In view of success with previous tests, a Heron-designed piston whose 2nd land width was increased 25% and with a filleted groove with 0.03" radius was planned for the first endurance trial; Prescott piston designs, along with salt-filled ones were planned for later tests.

Layouts of the compression spring coupling for supercharger and rear accessory had been revised. To improve location of coupling members, the inner portion was now fastened to the crankshaft and the outer portion carried the accessory drive gear located on the inner member on one end and rear case at the other end (Both members were centered on the overhung crankshaft rear end in the June 1933 design report). All aft accessories including the magneto drives were now collectively reversible instead of reversing individual units; the magneto had previously required breaker cam resetting. The vacuum pump was now located aft instead of its original position at the engine front. This change used a long shaft to drive rear accessories from the engine front with individual drive gears on the propeller drive gear and resulted in a 3 – 5 lb weight increase. The long shaft drive had pinions supported on each side, providing greater torsional flexibility and a lower torsional period; it was driven by a member with minimal torsional amplitude though subjected to total engine torque variation.

Details of ignition system radio shielding had been received from the Breeze Corporation. Ignition system layouts were being revised for weight analysis and USAAC approval. The intake manifold had been revised to give a circular cross-section and non-rigid supercharger connections.

A study was made of propeller reduction gear support loadings. The original 22 Jun 1933 design had a bearing support between gear sets and an arrangement without bearing between gear sets. The latter arrangement required one less structural diaphragm, less nose section joints and load transfer to the case was simplified. Layouts were in process to determine feasibility of the later scheme. Pitch, tooth dimension and pressure angle data with standard cutters for Sykes type herringbone gears for the three contact ratios had been received.

Heat treatment and physical property specifications for Y-alloy used in the single cylinder heads casting and for future heads was received from Mr. Welty of ALCOA. An analysis was made of crankshaft bearing loads, crankshaft and main bearing unit pressures and comparisons made with other engines. This was reported in Design Report No. 55.

[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 21 – 26.]

21 Mar 1934. Kinnucan released Design Report No. 55, Continental O-1430-1 Engine: Crankpin and Main Bearing Loads.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 55 – 79.]

Tilley's Reversible Starter/Generator Scheme

2 Apr 1934. Prescott published Memorandum Report No. E-57-126-5 documenting a 29 Mar 1934 conference between Continental's Furry, and J.H Rosche and Ford Prescott of the Engineering Division regarding the O-1430-1 engine. Aircraft Brand proposed that the starter and generator mount be revised, as mounting these on an angle to secure more compact cowl lines. It was pointed out that this would considerably weaken the starter drive, since the starter bevel pinion would be overhung on closely spaced bearings. It was decided not to give this further consideration , but to move these accessories down and aft as far as practicable., but retain the present general arrangement because of the favorable conditions for preventing oil from flooding the starter and generator. The Aircraft Branch was to complete a cowl sketch, A print of which was to be forwarded to Continental.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 80.]

2 Apr 1934. Prescott issued Memorandum Report E-57-431-1, Generator Mount Flanges, to recommend generator mount changes. In the past, very small and light generators had been used on aircraft engines. For these, the pad with four 5/16" stud s on a 5" bolt circle was amply strong. Generators had increased in weight until generator breakage has occurred and braces had been, in some cases, necessitated. It appeared that a better flange should be provided for larger generators.

Engines were increasing in power and the two-engine airplane appeared to offer many advantages for military service. In these engines, it was desirable to rotate the two engines in opposite directions. This was especially important in large geared engines. One method of using the same starter and generator on clockwise and anticlockwise rotating engines was to provide two identical pads with interchangeable starter and generator adapters so these units could be interchanged to provide the same accessory rotation for either engine. This necessitated a transition piece to adapt the 4-stud generator flange to the 6-stud starter pad, or a redesigned generator flange that would fit the 6-stud starter flange.

The PPL recommended that large generator for six 0.375" studs on a 5" both circle with 4.125" diameter pilot be considered. This would have simplified the O-1430-1 engine design, which was arranges so that either ether rotation could be secured by engine changes. Continental drawing No. SK-18 set forth the advantages of the propose flange reversibility as necessary.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 81.]

3 Apr 1934. Kinnuncan published Design Report No. 56, Continental O-1430- Engine: Load Analysis for Two Propeller Reduction Gear Arrangements.[USNARA RG343 RD1670, 502-2-108 O-1430-1 Propeller Reduction Gear.]

6 Apr 1934. Tilley issued a progress report for the period ending 31 Mar 1934. The Heron-type sodium-potassium filled (NAK) piston mentioned in the previous progress report was modified and installed in the engine with two lapped steel rings. In preparing for upcoming endurance testing, delays had occurred due to test setup failure due to lack of effective oil cooling, low oil pressure, faulty indicator, differences with the new carburetor and its large plenum tank.

During the week ending 24 March, Dr. Sanford Moss of General Electric conferred with Continental regarding the XO-1430 supercharger. Moss was advised of requirements and took with him a preliminary layout of the proposed supercharger; Continental was awaiting his recommendations.

Continental drawing SK 18 showing proposed use of A-N Standard starter support for larger generators instead of the present four-bolt flange with small pilot was submitted to the PPL. If adopted, this arrangement saves the weight of an adapter now required and provided more adequate support for horizontally-oriented generators as required for the XO-1430-1.

Separate radio shielding layouts incorporating General Cable's recommendations were made for the proposed cylinder design. These were not to be submitted for final approval until cylinder design was approved. The Breeze shielding was about 6 lb lighter than the General Cable. F.G. Gardiner, Breeze Corporation Chief Engineer, met with Continental on 30 March to review layout of Breeze shielding and promised further data to permit reduction of individual lead lengths, thereby further reducing weight. Preliminary gear train drawings were made for both propeller rotation directions and were to be submitted to Wright Field for comment along with propeller reduction gear and accessory drive layouts. Detail propeller reduction gear construction layouts, including case, starter, generator and accessory drives were nearly complete. Final rear crankcase layouts, including accessory drives were nearly complete. Final main crankcase layout had been started. Crankshaft detail had been started.

The crankshaft and reduction gear natural torsional vibration analysis was computed, and a report was to be submitted after the computations were checked. The resonant engine speeds for 6, 4.5, and 3.5 order (Stieglitz) were well below the operating range. The 1.5 order was being further investigated. Crankshaft, reduction gear quill drive, and supercharger drive stresses had been estimated, but required checking before reports were completed.

Three copies of preliminary Report No. 56, Continental XO-1430-1 Engine: Load Analysis for Two Propeller Reduction Gear Arrangements accompanied this progress report. The object of this analysis was to determine the bearing and surrounding reduction gear case loads, in order that proper consideration be given to construction types other than given in Continental Report Design of 1,000 hp Flat Engine Dated 22 Jun 1933. A detailed analysis of the original construction with a center bearing, called "Construction #1", and an analysis of a compact construction without the center bearing, "Construction # 2" was given.

The employment of one diaphragm (Construction # 2) to carry, and hence concentrate, the front end loadings into one plane, minimized the loading on the reduction gear housing outer shell. While the two constructions shoed differences in rear diaphragm loading, this was due to the more spread out supports for # 1. The propeller shaft stiffness was sufficient to avoid front end bearing cramping of the 1st stage pinion, or throwing the gear teeth out of alignment. It was concluded that Construction # 2 was somewhat lighter for the same strength and stiffness, and was believed to be the best suited for the O-1430-1 engine. [USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 82 - 86.]

14 Apr 1934. Ford Prescott issued Memorandum Report E-57-126-6 covering a conference on the O-1430-1 Engine held on 23 Mar 1934. Tilley and Furay represented Continental, and Capt E.M. Powers, Chenoweth and Prescott represented MatCmd. The parties agreed that the supercharger design should be complete since the contract specified complete detail and assembly drawings. Continental wanted to postpone paying a consulting fee to General Electric until the contract was signed for construction of the complete engine.

The PPL recommended a large generator flange, identical to the starter flange, in order to simplify reversing the O-1430-1. The original generator flange was inadequate for the large generators then in use by the USAAC. Two identical pads with starter and generator dog adapters, rotating in opposite directions, would allow using identical accessories on clockwise- and anticlockwise-rotating engines in twin-engine aircraft. By changing the Cuno mounting flange the same filter used on the Allison V-1710 could also be used on the O-1430-1; this proposal was adopted.

Continental was instructed to pack the joint between the Government-furnished NA-R7 carburetor and its mounting pad in order to stop an air and fuel leak. This carburetor had produced low engine power; its venturi size was enlarged, after which the results were identical to those of previous tests.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 99 – 100.]

16 Apr 1934. Kinnuncan published Design Report No. 57, Continental O-1430- Engine: Reduction Gear and Propeller Shaft Bearing Loads.[USNARA RG343 RD1670, 502-2-108 O-1430 Prop Bearing Loads.] and Design Report No. 58, Continental O-1430- Engine: Fundamental Frequency of Torsional Vibration of the Crankshaft and Reduction Gear System.[USNARA RG343 RD1670, 502-2-108 O-1430 Torsional Vibration.]

16 Apr 1934. Tilley issued a progress report for the period ending 15 Apr 1934. The previously reported Heron-type piston was run in for 15.5 hrs, attaining 2,500 rpm, 0 inHgA intake pressure, and 250°F jacket temperature. The cylinder and piston were removed from the test engine. The steel piston ring in the top groove and two cast iron compression rings were worn and feathered. The cylinder was lapped to remove streaks on the walls. The same piston was reassembled with new Muskegon Piston Ring Co. cast iron rings and run in for about 6 hrs. While running at 5 inHgG, no power increase occurred with further increase of manifold pressure. The top ring had worn until a 0.025" deep groove was nearly gone. The other rings were also worn, but to a lesser extent. A NAK piston with American Hammered Company rings (cast iron) was assembled with a 0.015" skirt clearance. The engine was run-in for 6 hrs up to 2,500 rpm, 200°F jacket temperature and 60 psi bmep. Thereafter, the piston was OK, rings coming in with slight feathering, mostly at head end edge. The run-in was continued with 250°F jacket temperature and 60 psi bmep, increasing speed to 3,000 rpm, when the piston seized. Inspection showed scoring at each side adjacent to relief (4 places) deepest at skirt crank end. The aluminum was readily cleaned from the cylinder with a stone by hand. Maximum out-or-round or taper was about 0.003". The cylinder was reground with boiling water flowing through the jacket to 0.0095" oversize hot. Cold, the bore head end was round and 0.003" oversize mid-section under jacket was round and 0.0055" oversize; under the hold-down flange and crank end was round and 0.0075" oversize. The second NAK piston was reground 0.005" undersize, and the side relief increased 0.5" on each side. The final skirt clearance became 0.023 to 0.275 below the jacket and in the jacket respectively. The crankshaft pin ran true. The rod showed 0.005" out of parallel and 0.003" twist in 5". The small end was rebushed and bored to be in line with the crankpin.

The engine was assembled with American Hammered rings without lapping the cylinder bore. It was run-in 8 hrs up to 2,500 rpm, 250°F jacket temperature, and atmospheric intake pressure. The cylinder was removed for inspection. The 2nd and 4th rings were broken about 1" from the gap. All rings showed uneven bearing. There was not feathering.

The piston was reassembled with three new steel compression rings without a ring in the top groove. The engine was run-in 8 hrs and up to 2,500 rpm and 105 psi bmep. Inspection showed rings OK except for slight feathering on the top ring. This feather was removed, the rings replaced and run-in continued. A revised Heron-type piston (with 0.563" top land, more backing behind ring belt and skirt, and reduces central circular ring fine) casting was promised for 15 April. A new cylinder barrel, jacket and head casting was in work. The barrel thickness for the upper 2.5" was being increased 0.032", or approximately 2%. This action was taken to provide less probable distortion under load in the event present action was inadequate.

Dr. Moss's recommended supercharger data submitted to date was satisfactory. Revised drawing SK21 sheets 1 and 2 were mailed to Dr. Moss for approval or recommendations and further data. Final propeller reduction gear layout, incorporating the three ratios specified, and the detail construction as previously reported, was in progress. The rear crankcase layout was being revised to make it more compact. Final main crankcase layout was in progress. Layouts and studies of accessory and supercharger drive gear tooth contours for best tooth form was in progress. Crankshaft detail was complete and was to be submitted separately for approval or comment after it had been checked.

Three copies of Design Report No. 57, Reduction Gear and Propeller Shaft Bearing Loads, No. 58, Fundamental Frequency of Torsional Vibration of Crankshaft and Reduction Gear System, and No. 59, Crankshaft Stress Analysis accompanied this progress report. A study was in progress to select from harmonic analysis of single-cylinder torque curve the cumulative components for the O-1430-1 engine and proposed firing orders.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 102 – 104.]

2 May 1934. Tilley submitted a progress report for the period ending 30 Apr 1934. Single-cylinder testing continued to 4 hrs and 3 inHgG at the carburetor, 3,000 rpm and 109 psi bmep. Inspection revealed the cylinder bore was scratched. It was reground hot to 0.0095 oversize cold (under the jacket), reassembled with new oversize piston with 0.563" top land, new 0.010 oversize American Hammered rings, one 0.125" top ring and three 0.094" compression rings. The cylinder was run-in for 8 hrs up to 2,500 rpm and 94 psi bmep. The rings were worn and the gaps had increased by 0.010". The ring edges were removed and the cylinder smoothed with crocus cloth. The run-in was continued for 5 hrs to 9 inHgG, 153 psi bmep and 3,000 rpm. At 10 inHgG the bmep was only 148 psi and bad blowby began. Inspection showed all rings to be badly worn; the top ring gap was 0.085" and the bottom gap was 0.045". Ford Prescott witnessed this inspection.

The cylinder bore was cold honed by Hutto Engineering Company to 0.013" oversize. A new piston was prepared with a 0.5" top land including a heat dam (an empty groove between the piston crown and first ring intended to reduce the heat reaching the first ring), three 0.125" compression rings and one 0.188" oil ring, all with reduced side clearance, which gave a 2.5" skirt length. The piston was assembled with three American Hammered compression rings and no oil ring. It was run-in for 6 hrs to 70 bmep, 2,500 rpm. Inspection showed ring gap had increased by 0.017", 0.007" and 0.011", top to bottom. These ring were replaced with American Hammered rings machined with a 1° face taper. Another 6-hr run-in to 70 bmep and 2,500 rpm eliminated the face tapers and increased the gaps by 0.024", 0.016" and 0.014"; the cylinder was scratched and rough. The cylinder was disassembled in order to replace the barrel with a carbon steel barrel with a 21 Rockwell C hardness. U.S. Hammered piston rings were promised for 5 May 1934. A new piston was machined from forged Y-alloy except for final diameters and ring belt. One nitralloy, one SAE 1050 carbon steel, and one chrome molybdenum cylinder barrels were in work as well as a cylinder head casting and jacket. A new assembly was to be completed during the week of 7 May 1934.

A main crankcase details drawing was started and an oil pump layout drawing was completed. Main crankcase layout drawings continued, as did the propeller reduction gear layout. Data from Farrel-Birmingham regarding gear tooth contours had not been received. The study of gear tooth contours for accessory and supercharger drive gears was completed, as was the rear crankcase and accessory drive layout.

Crankshaft detail was waiting on No. 1 counterweight hole dimensions for boring Nos. 3 and 4 crankpins, and harmonic analysis. Supercharger layout was pending receipt of data from General Electric. Sketches of the proposed outline were submitted to General Electric on 13 and 18 Apr 1934 for its approval and diffuser design. Load and stress analysis of the main crankcase and supports was in progress, and harmonic analysis of single-cylinder torque cumulative components were awaiting an indicator card.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 105 – 108.]

17 Apr 1934. Kinnuncan published Design Report No. 59, Continental O-1430- Engine: Crankshaft Stress Analysis.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 118 – 130.]

15 May 1934. Tilley published a progress report for period ending this date. During an attempt to remove the cylinder head from the barrel in a castor oil bath at over 600°F, seizing left aluminum in the 4th through 6th threads from the barrel head end. There was probably poor thermal contact, which may have contributed to this barrel's history of ring wear. This and other cylinders was to undergo metallographic examination to determine if cylinder material might have been a factor.

The SAE 1050 steel barrel was assembled to a new head with a 0.016" shrink fit, new valve seat inserts, but original valves, springs, studs, etc. The original jacket was used with the bore reground 0.010" oversize and the head land turned to fit. The last piston, mentioned in the 30 Apr 1934 progress report, was machined to standard diameter. Three American Hammered compression rings and no oil ring were used because of U.S. Hammered supply chain delays due to a strike. The cylinder was run in for 6 hrs to 70 bmep and 2,500 rpm, and then dismantled. Inspection showed rings wearing in nicely. The run-in was completed to 3,000 rpm and 144 bmep, and the cylinder again inspected; bore and ring condition was satisfactory. The cylinder was reassembled with U.S. Hammered rings. After 2 hrs running to 2,500 rpm and 90 bmep, inspection showed the ring gaps had increased from 0.025" to 0.043". The cylinder was reassembled with the previously-used American Hammered rings and run-in continued to 16 inHgG intake pressure, 214°F intake temperature, 3,000 rpm and 164.5 bmep (216 imep). An attempt was made to obtain Farnborough indicator cards, but breakage of two balanced pressure valves and vibration prevented obtaining good cards. The engine was run for 2:10 hrs above 200 imep. The Prescott indicator was installed and rum for about 1.5 hrs without obtaining a satisfactory card. The cylinder was removed for inspection, found OK, and reassembled.

The engine was run for 1 hr under contract conditions with the Farnborough indicator without getting a good card. The fmep at 15 inHgG intake pressure was 47.2 psi. An endurance run was started under contract conditions; the bsfc was 0.55 or 0.44 lb/hp/hr. A 5:25 hr run brought the total endurance run time to 8:30 hrs above 200 imep with a 215°F carburetor air temperature.

Direction of rotation charts for crankcase analysis and the main crankcase layout were complete.

Work continued on the main crankcase right and left halves, and propeller reduction gear layout, using Farrell-Birmingham gear data and recommendations.

The crankshaft detail was held up pending receipt of data regarding the No. 1 counterweight through-hole diameter to accommodate boring No. 3 and 4 crankpins, and harmonic analysis. Supercharger layout was held up pending data from General Electric. Sketches of the proposed outline had been submitted to GE on 13 and 18 Apr 1934 for approval and diffuser design. Propeller reduction gear layout was held up pending completion of coolant pipe layout.

Main crankcase and supports load analysis was in progress. Single-cylinder torque cumulative component harmonic analysis was awaiting a good indicator card from the test engine.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 142 – 144.]

22 May 1934. Prescott issued Memorandum Report E-57-126-8, which reported on a conference at Continental where he met with Kalb, Tilley and Carl Bachle about O-1430-1 single-cylinder tests. The matter of excessive piston ring and cylinder barrel wear on the test engine was discussed in detail. It was observed that cylinder scoring or picking up of small particles was occurring, not only on the piston's thrust side, but equally all around. New piston rings with 1° face taper had been ordered from U.S. Piston Ring Company, and would be installed with the large end down. It was hoped this would result in better ring belt lubrication by holding the oil below the rings. More than 50 hrs of various kinds of running up to 10" inHgG boost had been accomplished, and had brought out several interesting facts. Scoring after about 34 hrs necessitated regrinding the cylinder, but it appeared that the piston used had insufficient clearance and should have been examined at intervals, and when rubbing occurred should have been ground down to increase the clearance. This piston was an experimental internally-cooled piston and was intentionally made with small cylinder clearance.

A new piston of the circular rib type was fitted after regrinding the cylinder to 0.010" oversize. Excessive blow-by developed at about 16 hrs, necessitating examination of the piston and cylinder. It was found that ring wear and cylinder scoring were again bad enough to require cylinder refinishing. The valves and seats were in good condition, but slight cracking of the Stellite exhaust valve stem tip had occurred. This was not thought to be serious enough to cause trouble. The piston rings used were U.S. hammered rings without tapered faces. The rings gave evidence of being too dry, notwithstanding the excessive oil consumption. This SAE 4130 cylinder sleeve, with a Brinell hardness of 320 to 350, differed from the conventional SAE 1050 steel sleeve at 150 to 200 Brinell. In view of the excellent results secured on sleeve valve engine with Nitralloy sleeves, Continental was making a new Nitralloy sleeve with 0.031" thicker walls than present. This was to be tried in the effort to overcome ring wear. Two additional cylinder heads and jackets were also being machined. A forged Y-alloy piston was being machined and was to be compared to the cast Lo-Ex pistons furnished by the Government. A cast piston of more conventional design was to be tried when a new barrel of correct bore became available.

Tilley complained that Continental was unable to purchase the fuel specified for the test unless it had a Government permit. The fuel was specified to be not better than USAAC Specification No. Y-3557 and containing not less than 4 cc tetraethyl lead per gallon. In conversation with S.D. Heron, now at the Ethyl Gasoline Corporation, it was learned that Ethyl would cooperate in Continental's obtaining fuel to meet the requirements, and would send someone to Continental to lead the fuel. Heron stated the requirement could be met by blending two available fuels and then bring up the lead content to 4 cc per gallon.

Prescott felt that the present troubles could be overcome and Continental was doing all in its power to push the project to a successful conclusion. However, he also felt that Continental should not have waited for final contract approval before proceeding with the cylinder test work. This had delayed the development work by many weeks. No 12-cylinder drawings could be approved because successful single-cylinder test work was a prerequisite to 12-cylinder design approval. It was required that all articles called for in the contract be completed 190 days from the date of the contract, which after much delay was finally approved on 13 Feb 1934. The available time from date (27 Apr 1934) was only 114 days to 22 Aug 1934. Six men were in the Dayton office and Tilley was devoting about half his time to the Dayton organization. MatCmd was rendering full and complete cooperation and planned to approve details of the assemblies to be furnished on this contract as soon as the contract terms were met.

[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 131 – 133.]

25 May 1934. Continental Test Engineer Carl F. Bachle released Aircraft Engine Report #105, Report of 50-hour Endurance Test of Continental Hyper Engine No. 2A.[Author's Collection]

26 May 1934. Prescott issued Memorandum Report E-57-126-9 on the O-1430-1 Engine, outlining results of a 5 May 1934 conference attended by Long, Tilley, Furay and Morehouse of Continental and Chenoweth, Prescott and Wilson of the Division. Long presented figures for completion of the first 12-cylinder engine, with breakdown into phases for partial payment:

On the basis of the revised estimate, an Authority for Purchase was to be initiated to cover phases 1 – 6, leaving phase 7 until funds became available. Long explained that labor and material costs had increased substantially as a result of the National Recovery Administration and Wilson pointed out that the increase of about 12% was in line with other increased costs to the Government from this cause.

A question arose as to who should furnish the accessories for development tests. It was stated that the contractor should supply these, except possible a fuel charger, in order to eliminate the factor of failure of Government furnished material, which might be the cause of engine failure.

The then-present setup contemplated the contractor would furnish a carburetor for the development tests, but provision was made in the design for installation of a fuel charger. It was decided, in case of running the development test with the fuel charger, the cost of the carburetor would be deducted by the contractor; the Government was to pay for or furnish the fuel charger and nozzles for the development test. It was stated that it may be found advisable from the fuel distribution standpoint to use the fuel charger and this could be handled by a change order if the action was necessary.

Continental was admonished to expedite progress on the project and not to permit any further delays in carrying the work forward. Completion of the first engine was entirely predicated on successful completion of the current contract, particularly in relation to the single-cylinder tests and development. Government rights to tools, dies, patterns, jigs, etc., as mentioned in the then-current contract, were limited in the case of forging dies, not the property of Continental, to assignment of rights to the Government.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 138 - 140.]

31 May 1934. Tilley published a progress report for work through 31 May 1934. The 50-hr single-cylinder test at 211 imep and 3,000 rpm was accomplished successfully. The cylinder was OK except for fractured oil ring, which had not interfered with engine operation or damaged other parts. The test engine was also taken apart for inspection. The connecting rod, which had operated for about 180 hrs, mostly at 3,000 rpm and 83 ihp, had a fine crack adjacent to one of the bolt holes. A tooth was broken from the bevel gear on the vertical shaft, part #123, which meshed with the crankshaft bevel gear. Babbitt was cracked and small areas gone from the balance rods. The balance rods were being re-Babbited, a new connecting rod was being made and a new gear being obtained. The engine was expected to be running again during the week of 4 June.

The spare cylinder with Nitralloy barrel was complete. A forged Y-alloy piston was complete except for ring grooves and finished overall diameters, these being held up pending results of tests on the present piston. Piston rings from American Hammered with expanders, U.S. Hammered, and special alloy Perfect Circle were on hand. Metallurgical examination of the SAE 4130 and SAE 1050 barrels was partially completed.

A sketch of the supercharger mounting flange had been made and forwarded to General Electric. An installation drawing made from latest layouts, propeller reduction gear layout, coolant pipe and camshaft housing drain pipe layouts were still in process.

The crankshaft detail drawing was still held up pending #1 counterweight through-hole diameter to accommodate boring #3 and #4 crankpins and harmonic analysis. Rear crankcase detail and supercharger layout were waiting on GE to answer Continental's comments on a drawing received from GE on 22 May.

Main crankcase, gear case, and support load and stress analyses had been made and would be reported later. Preliminary harmonic analysis of single-cylinder torque cumulative components required for final crankshaft check was still waiting on a good single-cylinder test engine indicator card.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 147 – 149.]

4 Jun 1934. Prescott issued Memorandum Report E-57-285-1 documenting a 29 May 1934 conference at Continental involving Tilley, Furay, Morehouse and Kinnucan of Continental, and Roche and Prescott of MatCmd.

On the basis of crankcase and mount stress calculations, it was thought that a different O-1430-1 mounting method might be required. Further discussion brought out the fact that a slight misconception of force action within the engine structure existed, and this cleared up the matter; a new calculation was to be made. It was agreed that the four engine attachment points must be held in a plane coinciding with the aircraft firewall in order not to impose excessive engine structure stresses. Upon completion of the engine mount calculations, it was recommended that the additional layouts and calculations be made on the airplane structure to which the engine was to be mounted.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 150.]

7 Jun 1934. Memorandum Report E-57-285-2 chronicles a 31 May 1934 conference with Continental representatives Furay and Morehouse and MatCmd representatives Brelsford, Prescott, and Lt Watkins regarding O-1430-1 breathers and vents. Several breather designs were shown, one in the accessory drive housing at the engine rear, and one in the nose casing ahead of the reduction gears. MatCmd believed that the 1.125" ID size shown was not too large for ample breathing, but the front breather was relocated slightly, so that its open end was 0.313" to 0.375" from the revolving propeller shaft. By this means an effective baffle or shield was provided, which should have maintained oil tightness under all possible maneuvers. The rear breather was also located so that no oil could be thrown into it, an both were of such length that they offered a standpipe height of about 3" when the engine was inverted. Two 0.375" pipe bosses were located, one on either side of the rear accessory housing, and also one boss on the nose casting to provide oil tank venting. Provision was also made in the breather caps for vent pipes to the carburetor entrance. These provisions were considered ample and were to be incorporated in the design.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 151.]

8 Jun 1934.Capt A.J. Lyon, Engineering Section Acting Chief, wrote Continental about a gasoline sample it had submitted on 28 May 1934. The sample, submitted through Prescott, had been tested in accordance with Air Corps Specification 3566 and found to be slightly poorer in anti-knock value than Standard Reference Fuel C-6 with 3ml of tetraethyl lead per gallon. The sample, containing 5.5ml of tetraethyl lead per gallon, conformed with the anti-knock and lead content requirements of engine test gasoline.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 152.]

15 Jun 1934. Tilley released a progress report for the period ending 15 Jun 1934. A new single-cylinder connecting rod, cap and bolts had been made, the auxiliary rods were re-Babbited, the exhaust valve tip and seat were re-stellited, new piston rings with expanders were fitted, and the test engine was reassembled. After run-in, the cylinder parts were in good condition. Indicator cards were taken at 3,000 rpm and 211 imep with both Farnborough and Prescott indicators.

The engine was run for 4 hrs at 210 imep and 3,000 rpm to check the setup prior to the next 50-hr test. Total time to date for this cylinder at 3,000 rpm and above 200 imep was 60 hrs. Inspection showed a crack in the piston boss adjacent to an inner annular rib. The rob was thin at this point due to excessive diameter of the machined facing, and the rib had been filed to eliminate the notch in the recess. The oil ring was broken as in the first 50-hr run. The exhaust valve face showed a pit that did not disappear when lapped to its seat. While awaiting return of this valve from Wilcox-Rich Company, a new valve was placed in the cylinder. The piston described in the 30 Apr 1934 progress report was machined to fit the new 5.500" cylinder bore. This piston had a 0.563" top land with heat dam and was fitted with a 0.125" American Hammered ring with expander in the top groove, and three 0.094" American Hammered rings with expanders in the other compression-ring grooves. A 0.18" Perfect Circle oil ring was fitted. The engine was run in, disassembled and inspected; all parts were in good condition. It was then reassembled and a checks on operating conditions for the 3,300 rpm test and for 240 imep started.

A rear crankcase weight analysis had been started but not completed.

[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 154 – 156.]

20 Jun 1934.Continental Design Engineer James. W. Kinnucan released Design Report No. 61, Continental O-1430-1 Engine: Load Analysis of Crankcase, Gearcase and Support Plates.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 157– 165.]

22 Jun 1934.Continental Design Engineer James. W. Kinnucan released Design Report No. 62, Continental O-1430-1 Engine: Stress Analysis of Crankcase, Gearcase and Support Plates.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 156– 175.]

28 Jun 1934. Prescott published Memorandum Report E-57-126-10 concerning Contract Nos. 33-1650 and 33-3812, which covered the design and development and test of Continental poppet valve cylinders, which, if satisfactory, would lead to a 1,000 hp engine.

a. The Continental 4.625" bore x 5.000" stroke cylinder, of composite aluminum and steel construction as shown in Fig. 2 of Continental Design and Engine Adaptation of High-Performance Liquid-Cooled Cylinder" was suitable for operation at 3,000 rpm at 250 bmep with jacket temperature at 250°F and carburetor air temperature at 60°F. This cylinder did not result in a small compact engine as was hoped. High bmep required more supercharge than was economically feasible with existing supercharger types. A larger displacement at lower bmep appeared to be a more practicable solution. The PPL recommended that consideration of small-displacement high-output cylinders be abandoned at present in favor of more displacement and lower bmep and supercharge.

Introduction. The Hyper No. 1 cylinder was the outgrowth of a number of studies of possible cylinder constructions. After being tested under conditions simulating the required multi-cylinder performance, studies were made of this cylinder adapted to a 12-cylinder vee. Both upright and inverted Vee constructions were laid out.

The cylinder selected for build and test was of aluminum and steel construction. The head was Y-alloy, screwed and shrunk onto the SAE No. 1050 steel barrel. The steel jacket was shrunk on over a head casting extension backed up by a straight cylinder barrel portion, which was also shrunk onto a flange on the barrel at the lower end of the jacket. One intake and one exhaust valve were used. Both valves were sodium-cooled and were seated in aluminum-bronze seats. The exhaust valve was stellite-faced. A full description of the cylinder and engine was contained in Continental's report on Performance and Endurance Test of Continental 'Hyper Engine No. 1,' dated 6 Feb 1933.

Further details of test methods may be found by reference to the Continental Report referred to above and to the Report of 25-hr Development Test of Continental Engine No. 1, dated 3 Mar 1933.

The 12-cylinder design studies required by PO No. 33-1660 covered a 1,000 in³, 800 hp engine. Layouts were made incorporating the 4.625" x 5.000" Hyper No. 1 cylinder in a 12-cylinder inverted vee engine. Layouts were also made around modified designs of 5.000" x 4.750" and 5.125" x 4.500" vee and hex designs. Table 2 gives a summary from the analysis of these designs.

Further details of this work phase were available in Continental Report on Design and Engine Adaptation of High Performance Liquid-Cooled Cylinder."

The single-cylinder tests proved it practical to operate cylinders at high output and that valves and pistons could be made to withstand such operation. However, spark plugs were a source of trouble for such work and it was hoped that intensive plug development would result in more suitable plugs for high-output engines. Cylinders with bores equal or slightly greater than their strokes appeared to be best adapted to high crankshaft speed. Crankshaft bearing requirements dictated greater cylinder center distances than normal. This made excellent cylinder construction with aluminum alloy heads and steel barrels screwed and shrunk together, and with steel jackets shrunk over the barrels. Coolant heat transfer appeared to be best accomplished using external connections between head and jacket. High output appeared to require supercharging in excess of what could economically be supplied by existing superchargers, and this factor indicated that, for the present, increased displacement at slightly lower bmep. Built-up, welded steel cylinder construction did not offer any advantage over steel and aluminum construction, and difficulties with welding and brazing made built-up construction undesirable.

For many reasons, including those stated above, it was decided to abandon the high-output project in favor of a middle course in which a bmep of about 185 psi at a 3,000 rpm crankshaft speed was to be used. This resulted in a 1,425.50 in³ displacement for a 1,000 hp engine with a 5.500" bore and 5.000" stroke. On this basis, a new cylinder known as Hyper No 2 was fabricated, tested and incorporated in a design known as the O-1430-1 engine. This design was an opposed 12-cylinder engine incorporating a geared supercharger furnishing sea level performance to 1,000 ft altitude, with further altitude supercharging accomplished with a turbosupercharger mounted under the engine. Divided manifolding with four nozzle box sections would eliminate overlapping exhaust impulses and increase the cylinder scavenging, thus furnishing an inherently efficient exhaust system. This engine was to be the basis of a complete report at a later date, and was mentioned at this time so as to close out the existing expenditure order.[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 176– 179.]

30 Jun 1934. Tilley issued a progress report covering work done during the period ending 30 Jun 1934. The carburetor mixture control needle was modified to hold fuel flow constant during operation at 3,300 rpm. After 1 hr at 215 imep, 3,300 rpm and 0.48 lb/hp/hr indicated specific fuel consumption, the cylinder was removed for inspection and a Prestone leak in the magnesium transfer connection repaired. The piston land between the heat dam and top ring as well as lands between 1 and 2, and 2 and 3 rings were cracked or broken about a third of the way around. The cylinder was reassembled using a NAK piston with a 0.030" top land clearance, 0.035" ring land clearance and 0.025" skirt clearance. It was reassembled with expanders behind the rings. The engine was run in for 6 hrs up to 15 inHgG intake pressure, 3,000 rpm and 144 bmep; it was then disassembled, inspected and found OK except for some top ring wear. It was reassembled, run-in for 3 hrs and then run 3:15 hrs at 3,300 rpm, 211 imep; this run was stopped because of blow-by.

Disassembly and inspection showed the top ring gap had increased from 0.025" to 0.080", the expander collapsed and 0.5" broken from its end. Several small ring fragments were found and one had scored the top land. All other rings were normal and the cylinder was undamaged.

A forged Y-alloy piston was finished machined with 0.035" top land, heat land and first ring land clearance, 0.030" for the other ring lands, and 0.025" skirt clearance. One oil and three compression ring grooves were machined. The engine was reassembled without a top ring expander, run in to 3,000 rpm and 211 imep, disassembled and inspected. The exhaust rocker arm fulcrum pin was broken through the oil hole in its center. The piston and rings were OK. A new fulcrum pin was installed and the engine was run in for about 0.5 hr up to 3,000 rpm and 211 imep when blow-by started. Inspection showed that the land between the heat dam and top ring was cracked half way around the piston.

The engine was reassembled with a salt-cooled piston, American Hammered compression rings, Perfect Circle oil ring and no expanders. New transfer passages were assembled as former ones were so corroded that they were not Prestone-tight. The engine was run in up to 3,000 rpm and 205 imep. The oil consumption was lower than before. The exhaust rocker needle bearing inner race was worn excessively and replaced with a plain bushing. The engine was run in for 0.5 hr at 3,300 rpm and 215 imep but stopped because of blow-by; the top ring gap had increased from 0.025" to 0.085" and the connecting rod had a longitudinal crack in its I-beam web extending from 0.5" above the big end portion to the small end.

The engine base was taken apart and inspected. The flywheel and crankshaft roller bearing had 0.007" radial play compared with 0.002" for the roller bearing at the other shaft end; these bearings were interchanged. A new connecting rod hammer forging was obtained from Wyman Gordon and the Continental shop promised a finished rod by 12 July. A cast Lo-Ex piston (part No. 500093 was finished for the next run. This had four compression rings, one oil ring and no heat dam. Top land clearance was 0.028", the two top ring land clearance were 0.032", the other ring lands were 0.025" and the skirt was 0.020". More piston casting and forgings were being obtained for stock.

The total run time for this cylinder at 3,300 rpm and 210 imep was 4.75 hrs, and 67:50 hrs at 3,000 rpm and 200 imep. Total running time of all kinds was several times these values.

Work continued on the Reduction Gear Rear Housing detail, and the main crankcase halves detail.

[USNARA RG342 RD1670, 502-2-108 O-1430 to 340630. 180– 183.]

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