Continental XO-1430 Development
Part 4: 1 Jul 1934 to 31 Dec 1934
by Kimble D. McCutcheon
Published 19 Aug 2025; Revised 24 Aug 2025

15 Jul 1934. Continental Chief Engineer N.N. Tilley released a progress report for the period ending this date. A new test engine connecting rod was completed on 9 July. The single-cylinder engine was assembled with a cast Lo-Ex (low expansion) piston, Dwg 500093, described in the last progress report. The engine was run-in gradually with teardown inspections at 3 and 18 inHgG at the carburetor and 3,000 rpm.

An endurance run was started at 3,300 rpm, 215 imep, 0.48 isfc and 210°F air intake temperature. Running continued for 35 minutes until blow-by became excessive. Teardown inspection showed the land between top and second ring was broken; cylinder barrel, rings and the rest of the piston were otherwise in good condition.

The fourth internally-salt-cooled piston was modified to give the following clearances: top land = 0.027"; ring lands = 0.035"; skirt = 0.023". A 1° bevel was made at the piston pin bore inner edges and on the skirt below the oil ring. This piston, with U.S. Hammered rings (full taper on upper surface) was run-in to 3,000 rpm and 200 imep. Inspection revealed that the top land was bearing toward the flywheel, the cylinder bore was 0.005" oversize at the head end, and the ring tapers were missing on the top ring and half gone on the others. The top ring was replaced with an American Hammered ring with 0.003" side clearance. After a 3-hr run-in and 2:25 hrs at 3,300 rpm and 217 imep, the top ring broke about an inch from each gap end. The other rings were excessively worn. The total run time for this cylinder at 3,300 rpm and 210 imep was 7:45 hrs.

The single-cylinder torque curve had been subjected to harmonic analysis and a Fourier series representing it had been produced. This would be combined with the crankshaft system static deflection curve to obtain the comparative resonance deflections.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 2 – 4.]

25 Jul 1934. During a conference at MatCmd, Tilley and Furey represented Continental, and Civilian Engineer R.M. Clarke and Capt E.M. Powers representing MatCmd. Continental reported that a forging was being obtained from the Wyman Gordon Company that would be used to make a single-cylinder connecting rod for testing the cylinder parts to be used in the O-1430-1 engine. The recently-failed connecting rod had not been machined from a forging. Tilley stated that piston rings clearances were being altered in an effort to eliminate the excessive piston ring wear. He also stated that experimentation with steel rings would continue.

Continental requested information regarding the present status of the Continental R-670 engine for training purposes, and were advised that the training engine scheduled for Air Corps use had not yet passed a standard 150-hr type test, a perquisite to any procurement.[25 Jul 1934 Memorandum Report E-57-285-4. Conference of July 6, 1934, with Messrs. Tilley and Furey of Continental Aircraft Engine Co., Regarding O-1430-1 Engine. USNARA RG342 P031284.]

27 Jul 1934. PPL civilian employee Ford L. Prescott authored Memorandum Report E-57-285-3, which reported the results of a 11 Jun 1934 conference at Continental attended by Tilley, Bachle, Kinnucan and Prescott. The second single-cylinder test engine was ready for the second 50-hr test. A lack of satisfactory spark plugs might have imposed limitations on high output engine power. The best results had been obtained with HT 300 plugs, but even these were good for only about 10 hrs. BG 157 plugs developed leaks in less than 5 hrs. Indicator cards were taken both with the Farnborough and MatCmd indicators, and these agreed closely except for the higher pressure portion of the card, where extreme point dispersion rendered the Farnborough card almost useless. Continental engineers believed that maximum, minimum, early and late cards could be distinguished, but this appeared to be in doubt. Rate of pressure rise measurements during combustion did not agree. In one case, the Farnborough gave a rate of 66 psi/degree while the MatCmd indicator gave 22.6 psi/degree. This may have been the basis for the very low 14.5° spark advance used for the first 50-hr test. Prescott thought this to be too low, a contention that was borne out during an 11 Jun 1934 run, where 30° or more could be used under the same boost conditions and rpm. Previous experience indicated that the spark advance should be in the 35° to 40° range at 3,000 rpm. This was also confirmed by the cards taken with the MatCmd indicator, although the Farnborough cards indicated a very early and abnormally rapid pressure rise. It was apparent that engine shocks, such as were produced by piston slap, could cause current interruption and give false pressure indications in the case of the Farnborough valve. Prescott admonished Continental to use extreme care in choosing the spark advance value used in the remaining two 50-hr tests, and also recommended that close cooperation in spark plug choice was essential to developing high specific output engines.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 5 – 6.]

31 Jul 1934. Tilley released a progress report for the period ending this date. The single-cylinder test engine was reassembled with four American Hammered compression rings and a Perfect Circle oil ring. After 40 min at 3,300 rpm and 208 imep, there was excessive blow-by. Inspection showed the first and fourth rings broken. The engine was reassembled with American Hammered rings from a new batch. After a 3-hr run-in, the engine was run for 1 hr at 3,300 rpm and 208 imep when bad blow-by started. Inspection showed the top ring had very little tension and its gap had closed; the cylinder bore and remaining rings were worn. The cylinder was removed to refinish its bore. The Nitralloy cylinder, which was 0.020" undersize, was assembled to the test engine with a NaK piston machined undersize to match. This was the used piston whose lands were grooved from expander or inner ring failure as reported in the 30 Jun 1934 report. The intake valve was new and the exhaust valve was from the first 50-hr test. After run-in, while operating at 4 inHgG and 3,000 rpm, bad blow-by started. Inspection revealed the American Hammered rings were not bearing near the gaps. Cylinder bore wear near the crankcase was 0.0005".

The Nitralloy cylinder was reassembled to the test engine with Perfect Circle 0.125" compression rings of DA alloy, but with 0.094" bearing face. After run-in inspection showed the rings were badly worn; gaps had increased by 0.031", 0.013", 0.030", 0.040" and 0.002", top to bottom. The Nitralloy cylinder was reassembled with U.S. Hammered rings. After run-in, inspection showed the rings and bore in good condition, after which the engine operated 5 hrs at 3,300 rpm, 215 imep with a 96°F air temperature. Inspection showed the intake valve spring broken because of interference between the lower intake spring retainer and cylinder head had cocked the spring. The interference was removed, new springs assembled, piston rings not replaced and the duration test continued for 3.5 hrs at 3,000 rpm, 211 imep, 190°F air intake temperature when blow-by occurred. No reason was found for this, but the exhaust valve seat was pounded in and its seat width had increased from 0.047" to 0.078". After 45 min at 3,300 rpm and 215 imep, bad blow-by again occurred for no apparent reason, except that the top, second and fourth gaps were aligned. The top ring was replaced because its bevel had worn off. During the subsequent run-in the piston seized due to scoring at the skirt edges in line with the pin boss. Later events pointed to Prestone in the oil from a leaky coolant pump gland. The total time for the Nitralloy cylinder at 3,300 rpm, ≥210 imep was 9:15 hrs; the piston had 12:30 hrs at 210 imep.

The carbon steel cylinder barrel was honed 0.014" oversize, fitted with the cast Lo-Ex piston with internal annular ring support for the pin bosses, machined for three compression rings and one oil ring as per Dwg 500123. American Hammered compression rings and a Perfect Circle oil ring were installed. Run-in was interrupted by Prestone leaking into the oil sump from a worn coolant pump shaft and packing gland. Total time on this cylinder was 9:25 hrs at 3,300 rpm and 210 imep; at ≥3,000 rpm and ≥200 imep, time was 72:50 hrs.

The multi-cylinder connecting rod study was still pending crankcase details; crankshaft detail was waiting on harmonic analysis; the rear crankcase detail and supercharger layout were still waiting on a GE quote.

An analysis to determine critical crankshaft rpm ranges had been completed and a report was being prepared.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 8 – 11.]

2 Aug 1934. Prescott reported the results of a 19 Jul 1934 conference at MatCmd. Tilley and Furay represented Continental; civilian engineers A.L. Berger, Chenoweth and Prescott represented the PPL. The group discussed data to be included on the O-1430-1 engine data plate and Continental agreed to submit a drawing for approval.

GE had not yet submitted a quotation on the supercharger design. It was apparent the GE wished to supply the entire supercharger, and Continental had asked for quotations on this basis, but also on the basis of GE supplying the impeller and engineering on the scroll and diffuser. MatCmd was ambivalent about which plan was followed, since the contract specified a GE-designed supercharger. Continental was advised to deal with GE through its Dayton office for closer cooperation with the Commercial Department.

A hydraulic control for two-position propellers, its package size and type of central valve were discussed, and a design was to be drawn up by Continental so that suitable bosses and engine connections could be incorporated in the crankcase and nose castings.

Continental requested information on the smallest supercharger outlet that could be used without undue pressure drop, in order to secure better part-throttle engine operation. After some discussion, it was decided that the outlet could be reduced to 5" diameter while keeping the inlet at 6.375" diameter. This reduced the duct area from 24.9 in² to 19.7 in² and increased the manifold gas velocity by 26.5%. MatCmd thought this the smallest that should be used in view of the possibility of using this engine to power bombers at 15,000 to 25,000 ft.[2 Aug 1934 Memorandum Report E-57-285-5. Conference at the Division on Continental O-1430-1 Engine. USNARA RG342 P031282.]

10 Aug 1934. Kinnucan published Design Report No. 60, Continental O-1430-1 Engine: Torsional Vibration Characteristics and Critical Speeds of the Crankshaft and Reduction Gear System. This Design Report references a paper by W.G. Lundquist.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 16 – 48.]

15 Aug 1934. Tilley published a progress report covering the period ending this date. The 0.014" oversize carbon steel cylinder with the latest cast Lo-Ex piston (Dwg 500123) was run-in and inspected. After 1:18 hr at 3,300 rpm and 211 imep the test was stopped after the piston, piston pin and cap bolts failed. The piston and cylinder barrel showed no sign of scoring or seizure. The time on this cylinder at 3,300 rpm and 210 imep was 10:18 hrs, and 74:08 hrs at or above 3,000 rpm and 210 imep.

The crankpin was reground 0.010" undersize to 2.865" diameter. New lead bronze rod bearings were obtained and a connecting rod forging (from Wyman Gordon) was being machined and was promised by 15 August. A new oil pump shaft was made and the new oil pump assembled to the engine. The bevel gear backlashes were adjusted to between 0.010" and 0.015". The damaged barrel was removed from the cylinder head and jacket. A new carbon steel barrel forging was ordered, and Y-alloy piston forgings were expected around 20 August.

The unsatisfactory results with piston rings at 3,300 rpm were brought to the attention of the American Hammered Piston Ring Co., the U.S. Hammered Piston Ring Co., and The Perfect Circle Co., for their advice and recommendations. The Nitralloy cylinder was reground 0.003" larger and polished. A new salt-filled piston was being machined to give more cylinder wall clearance. Testing with this cylinder was expected to resume about 16 August.

Work on checking the reduction gear and front accessory drive layouts, rear crankcase detail after GE finally provided data, and checking the left and right main crankcase halves. The multi-cylinder connecting rod study and supercharger layout continued to be delayed. Design Report No. 60 was released on 10 Aug 1934 (see above).[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 13 – 15.]

[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 49 – 50.]

31 Aug 1934. Tilley released a progress report for the period ending this date. The cylinder with the Nitralloy barrel and salt-filled piston with 0.033" top land, 0.038 ring belt and 0.027" skirt clearances was fitted with U.S. Hammered compression rings and a Perfect Circle oil ring was run in for 6 hrs. After satisfactory inspection, the run-in was continued to 3,000 rpm and 211 imep, at which time it was inspected and the top ring found bearing for half its height. It was run for another 55 minutes at 3,000 rpm and 211 imep and then stopped due to excessive blow-by. The rings showed excessive and the cylinder bore was worn at each end of the ring travel. The piston showed heavy bearing at 45° to the piston pin axis. The piston skirt was cam-ground to relieve the rubbing areas by 0.0055" on the pin axis. The cylinder was honed to remove the shoulders at the ring travel extremes and reassembled with Surety four-piece steel compression rings.

After a 1.5 hr run-in to 2,500 rpm with no boost, it was inspected. The rings had not seated and the piston skirt maximum diameter was 45° to the pin axis instead of 90°. The cylinder bore was smoothed and a new piston correctly cam-ground. U.S. Hammered rings were selected as 9:15 hrs had been previously successfully run on a set. This combination was run-in up to 3,000 rpm and 6 inHgG boost when bad blow-by occurred and the piston seized. The cylinder was re-ground to 5.586" diameter. A Lo-Ex piston with long inner annular boss support (the original design) was reground to give 0.034" top land, 0.040" ring land and 0.024" skirt clearances. American Hammered rings were used with 0.005", 0.003", 0.003" and 0.002" top, second, third and fourth side clearances. This combination was run-in to 2,500 rpm with no boost, inspected and found OK. Run-in was continued to 3,000 rpm and 211 imep, inspected, and found in good condition.

Endurance running at 3,000 rpm and 240 imep was continued for 1:40 hr. The piston oil jet became clogged and the cylinder was disassembled for inspection. Original tool marks were evident on all rings. The test was continued for 5 hrs. It was determined that temperature (CAT) of ≤150°F could be used with other conditions according to contract without excessive detonation, and other contract conditions could be met with 96 octane (Texaco plus 6cc lead) fuel. This run was made without the piston oil jet. An inspection revealed tool marks still on the rings and no cylinder bore wear. The endurance run at 3,000 rpm, 240 imep and 150° CAT was continued to 9:07 hrs when the oil pressure fell. Inspection showed the lead-bronze connecting rod lining had failed. The crankpin journal was worn and the two balance connecting rods were cracked at the cap bolt retaining notches. The cylinder, piston and rings were in good condition. The crankpin was reground and a new connecting rod bearing and balance connecting rods ordered. Testing was expected to resume in 2 – 3 weeks. Total time on this cylinder was now 19:07 hrs of which 10:10 hrs was at 3,300 rpm and 210 imep and 9.07 hrs at 3,000 rpm and 240 imep.

Propeller, reduction gear and crankshaft system torsional characteristics study continued.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 32 – 54.]

5 Sep 1934. Tilley sent the Engineering Section Chief a draft supercharger specification from which detail drawings would be prepared, and solicited comments; there were none.

[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 69 – 70.]

15 Sep 1934. Tilley published a progress report for the period ending this date. Two new balance connecting rods had been promised for 18 Sep 1934. The crankshaft had been rebalanced and new bearings fitted to the connecting rod. A second cylinder with a carbon steel barrel was built up using a head that had been run 74 hrs, and a third cylinder was being prepared with a Chapmanized barrel. The Chapmanizing process produced a glass-hard case with 9 times the abrasion resistance of ordinary case-hardening. The process involved bubbling ammonia through a cyaniding salt bath and holding the finished part in the gas stream, producing a case almost as hard as nitriding, but much more rapidly. In this case, only the barrel bore was to be hardened, so various coatings were being tested to inhibit the process for the remainder of the barrel. Two Y-alloy piston forgings had been machined except for ring grooves and final grind, which was to be done after considering the advice received from American Hammered, U.S. Hammered and Perfect Circle piston ring companies.

Layout drawings were complete except for the coolant pump, intake manifold, oil drain pipes, ignition system, mounting plate and final checks. Detail drawings and checking were complete except for the reduction gears including frond end rives and their housing, the main crankcase, the crankshaft and the rear accessory housing. Details were in work for the rear accessory drives, oil pumps, coolant pumps and standard small parts. A revised coolant pump and pipes layout was being made. GE had been authorized to make a complete set of supercharger detail drawings. Details of parts on test in the single-cylinder engine (cylinder and piston parts) only needed to be traced. Assembly drawings, parts lists and bills of material remained.

The single-cylinder test engine balance was checked. Its stiffness and inertia data when coupled to the dynamometer were being obtained to check torsional critical speed and the possibility of crankshaft whirling. Then-current thinking put the critical speed at 7,300 rpm. Torsional vibration calculations for the Ranger V-770SG engine, which had a quill drive and had been checked with a torsiometer. This comparison was to assist in estimating the O-1430-1 frequency with better accuracy.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 56 – 57.]

30 Sep 1934. Tilley released a progress report for the period ending this date. Test engine assembly was completed on 19 Sep 1934. This included the two new balance rods and a new connecting rod bearing. The crankshaft system was rebalanced, and the same Nitrided cylinder, original Heron-type piston and American Hammered compression rings (no oil ring) as was running on 31 Aug 1934. After run-in and 2 hrs at 3,000 rpm, 240 imep and 150°F CAT, an inspection showed slight ring wear, some piston deterioration due to the excessive oil consumption (1.33 gal/hr!), which had caused severe detonation. The balance rod bearings, rod bearing and cylinder bore were in good condition.

The engine was reassembled, but before full power was reached, excessive blow-by resulted in another inspection. Some ring gaps were aligned and the connecting rod big-end bearing was grooved circumferentially each side for a 90° arc and chamfered longitudinally at the lining split to increase oil feed to and oil throw-off from the bearing. The engine was run for 5 hrs at 3,000 rpm, 240 imep and 150° CAT. At each hour, pressure to the piston cooling jet was reduced until it was completely off; oil consumption was then 0.33 gal/hr. Detonation at the run's start was excessive so 96 octane Texaco gasoline was used. On 24 Sep 1934, inspection revealed that tool marks were still on all piston rings, there was no further piston deterioration and no cylinder bore wear. There were cracks in the upper connecting rod bearing, which was replaced.

The engine was run 10 hrs at 3,000 rpm, 240 imep, 150°F CAT using contract fuel. Subsequent inspection revealed the piston, rings and cylinders in good condition. The exhaust valve seat had two pits, the connecting rod bearing was cracked near a dowel hole and bearing lining was missing nearby. The connecting rod bearing was replaced with one that was 0.001" tight in the rod. The exhaust valve seat was refaced, and a new spark plug bushing installed to replace the one that had two threads exposed in the combustion chamber, caused by spark plug removals.

After running for 10 hrs at 3,000 rpm and 240 imep, the cylinder parts and rod bearing were in good condition. When reassembled and run for 0.5 hrs under contract conditions, the spark plug required changing, but the spark plug insert was stuck to the plug and came loose from the cylinder head. A new straight-thread flanged insert was installed. Total time on this nitrided barrel cylinder was now 46:32 hrs, of which 36:22 hrs were at 3,000 rpm and 240 imep. The remaining time was at 3,300 rpm and 210 imep. Total time on the cylinder head retrofitted with a new carbon steel barrel was 10:18 hrs at 3,300 rpm and 210 imep, and 74:08 hrs at ≥3,000 rpm and 210 imep. The 50-hr test at 3,000 rpm and 240 imep was expected to be complete on 2 Oct 1934.

Layout drawings were complete for all parts except intake manifold, ignition system mounting plate, some cylinder/piston work, and checking. Detail drawings and checks were practically complete for reduction gears and housing, main crankcase, crankshaft, rear accessory housing and drives, oil pumps, connecting rods and most standard parts. Coolant pump, cam housing, cam drives and cylinder detail drawings were in process, and work remained on camshaft, rocker, camshaft accessory, gun synchronizer, intake manifold, coolant manifolds, ignitions system parts, mount plate, assembly drawings, parts lists and bills of material.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 60 – 62.]

8 Oct 1934. Dr. Sanford Moss of GE informed Talley that the supercharger discharge opening was being discussed. The drawings provided to GE showed an elbow that was integral with the supercharger casing. GE thought it may be better to have the supercharger casing end in a flange close to the engine with provision for a separate elbow between the casing and intake manifold. However, GE proposed to deliver drawings according to the original scheme. Under discussion was whether carburetor or fuel injection was to be used, whether the intake manifolds were the same height as the carburetor/fuel injection, and whether the supercharger was to have a cooler before or after. The solution to these issues would influence the elbow treatment, which could be modified at any point.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 58.]

15 Oct 1934. Tilley published a progress report for the period ending this date. The 50-hr test at 3,000 rpm and 240 imep(2nd 50-hr run) was completed and the report mailed to Wright Field. The same piston ring set was used throughout this run; the longest spark plug run was 13.5 hrs.

The 50-hr test at 3,300 rpm and 210 imep was resumed. The parts were a cylinder head from the first 50-hr run, with a new carbon steel barrel, forged Y-alloy piston with 0.028" skirt clearance, and American Hammered compression rings. After the first run with 12 inHgG boost and 3,000 rpm an inspection revealed no problems. The run-in was continued to 3,000 rpm and 240 imep when bad blow-by occurred. Inspection revealed all parts in good condition, so the run-in was continued to 3,000 rpm and 210 imep, after which the engine was run-in was continued for one hour without trouble. Inspection showed the top ring gap had increased by 0.018" and the ring was feathered. The piston skirt was out-of-round by 0.018" at the bottom and 0.010" at the top. The engine was reassembled with new rings. The piston was modified with a bevel below the oil scraper ring. After a 5-hr run-in, the engine was run for 1 hr at 3,300 rpm and 210 imep. Another inspection revealed the piston was out of round 0.011" at the skirt top and 0.018" at the bottom. Reassembled with new rings and following a 5-hr run-in, another inspection revealed the piston out of round 0.011" at the skirt top and 0.022" at the bottom; the top ring gap had increased by 0.007". The cylinder was reassembled with a new third compression ring and beveled oil ring. After a 3-hr run-in and 52 minutes at 3,000 rpm and 211 imep, the piston seized. The cylinder head was cracked in the exhaust port behind the guide bore as with the previous cylinder. Total time on this head at the time of fracture was 78 hrs ≥3,000 rpm and 210 imep, of which 14:10 hrs was at 3,300 rpm and 210 imep.

The cylinder head mentioned in the 5 March and 30 April reports had threads chased, and a new carbon steel cylinder barrel was in the works. The cylinder jacket bores were being chrome plated and reground, permitting a third cylinder assembly to be available by 27 Oct 1934. The cylinder head pattern was to be modified per SK-37, which had been sent to MatCmd in a 9 Oct 1934 letter, and a fourth complete cylinder assembly was being prepared to insure cylinder development completion.

Layout drawings of all parts were complete except intake manifold, ignition system, mounting plate and checking layouts, which was about 50% complete. Details and drawing checks were practically complete for reduction gears and housing, main crankcases, crankshaft, rear accessory housing and drives, oil pumps, connecting rods, piston, cylinder, coolant pump, cam housing, camshaft drives and most standard parts. Preliminary drawings of the GE supercharger had been received. Details were in work for the coolant manifolds, camshaft, camshaft accessory drives and ignition system. Assembly drawings of the complete engine were being made. Work remaining included intake manifold, gun synchronizer drive, mounting plate and final parts list/bills of material. Van Dykes of these drawings were to be submitted by 31 Oct 1934.

[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 64 - 66.]

18 Oct 1934. Prescott published Memorandum Report E-57-285-7/E-57-589-1 confirming a 1 Oct 1934 conference attended by Tilley and Prescott regarding O-1430-1 engine and single-cylinder tests. This report introduces a new purchase order (PO) number 35-644 and two new expenditure order (EO) numbers 502-2-117 and 903-553. The group reviewed details of the single-cylinders to be furnished on Purchase Order 35-644 to be sure these cylinders closely represented the" Hyper No. 2A" design. The valve seats were to be of 18-8 stainless steel with 0.125" wide seats, unstellited, in view of the very satisfactory service obtained from the Hyper No. 2A cylinders. Only the horizontal intake-side spark plug boss was to be drilled and tapped 18 mm x 1.5 mm pitch, thus permitting installation of the MatCmd indicator to study high-speed valve timing. No insert was to be installed in this hole, but the two angled spark plug holes were to have bronze inserts. The cylinder head material was to be straight Y-alloy, air-quenched with a minimum 90 Brinell hardness. The shrink fit on the barrel was to be 0.010" to 0.013", a decrease over what was originally used, but conforming to successful practice in the 2A cylinders. The one-piece jacket construction was to be similar to the 2A jacket, as shown in Continental Dwg 500152. Both intake and exhaust valves were to be of one-piece construction with a hollow head and stem, filled with NaK amalgam, and with stellite faces conforming to the successful practice in the 2A cylinder. Continental was to notify MatCmd before head, barrel and jacket assembly so that prior inspection could be made; final inspection was to be made at Wright Field subsequent to delivery.

In connection with the O-1430-1 drawings, the cylinder head was not to include a boss, which was used on the single-cylinder for a temperature probe, or could be used for future fuel injection, but Prescott did not think this fuel injection method was likely to be used on this engine; further head cooling might be improved by its elimination. Continental submitted drawings showing the proposed propeller hub attaching parts, thrust bearing plate bolt circle and hydraulic propeller control. These were to be forwarded to the Aircraft Branch Propeller Unit for comment and suggestion. The oil pressure gage tap location was discussed and Prescott stated that it should be on the Cuno filter engine side so that actual oil system pressure would be shown.

The question arose as to whether a vacuum pump drive oil seal should be included, and it was decided that an actual oil seal was not required, but the space around the coupling should be provided with a drain and vent so that no vacuum would cause oil to be drawn into the vacuum pump. There was discussion about whether a carburetor or fuel charger would be used on the first engine. In view of the provision made for both, as called for in the original specification, Prescott suggested that drawings for the original carburetor installation, without aftercooler, be completed; no contract deviation would be required and an aftercooler and fuel injection system could be the subject of a later separate study. In order to make this possible with minimum cost, it was suggested that a flanged joint be provided between the supercharger and outlet elbow.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 67 – 68.]

31 Oct 1934. Tilley submitted a progress report for the period ending this date. The fourth single-cylinder assembly comprising a cylinder head of the original 2A cylinder, cylinder jacket from a previous assembly, and a new carbon steel cylinder barrel was completed. This was designated as third assembly in a previous report. While no running at contract conditions was obtained with the first assembly, the records were clarified by the revised designation.

The test engine was built up with the cast piston from the 2nd 50-hr test and American Hammered rings. A new lead-bronze big-end bearing was installed. A loose flywheel delayed run-in until the worn steel cone was replaced by a new bronze locating cone. Run-in was completed and the engine operated 1 hr at 3,300 rpm and 215 imep. Inspection showed that the top ring gap had increased by 0.043". This set-up was the same as the previous successful 2nd 50-hr run except the piston clearances were increased by 0.003". It was not possible to clean up the new cylinder bore to the exact previous undersize value. The top ring was replaced by a ring modified at Continental to reduce the gas pressure differential and place more duty on the 2nd ring. After run-in and 1:10 hrs at 3,300 rpm and 215 imep, the blow-by doubled; the top ring gap had increased by 0.017".

A special set of U.S. Hammered rings, which included the Continental modification was received. As the oil control ring required a 0.25" groove instead of the 0.188" existing groove, the oil control ring was omitted. Oil consumption was so excessive that the 0.188" groove was enlarged to 0.25" and oil control rings (two 0.125" slotted one face) were placed on the piston. After a 2-hr run-in the engine was run for 1 hr at 3,300 rpm and 215 imep. The ring gaps had increased by 0.128", 0.030", 0.021" and 0.030", top through oil control. Oil consumption was about 1/3 less than the previous runs with American Hammered rings, but averaged 0.025 lb/hp/hr.

American Hammered rings were installed on the piston; the top ring used no expander ring, but expanders were used on the 2nd through 4th compression rings. No oil ring was included. The rings after run-in were OK, but after 1 hr at 3,000 rpm and 211 imep, the top ring gap had increased by 0.016". The groove depth was less than specified by American Hammered, so it was machined to a value (4.996" to 4.960") for which inner rings were made. Four new compression rings, all with expanders or inner rings were installed on the piston. Inspection after run-in showed the rings OK, but after 1 hr at 3,000 rpm and 211 imep the gaps had increased by 0.007", 0.011", 0.010" and 0.008", top to bottom. The piston's second land was cracked.

A new piston casting similar to the one used in this test series was obtained. It was being machined with a 0.563" top land, 0.188" second land, 0.156" third land and 0.125" for the other lands. Provision for four 0.125" rings was made, the lower being vented for an oil ring. This piston was to begin running on 1 Nov 1934. Rings on hand or on order to continue this development included: steel rings with 60 Rockwell C hardness; Everdur bronze-insert ring; combinations of American, U.S. and Perfect Circle rings. The next run was planned using the American Hammered rings with inner rings as last tested – these showed the most promise. A cylinder head casting modified per SK 37 for the fifth cylinder assembly was promised by ALCOA's Cleveland Foundry for 6 Nov 1934. Total time on cylinder No. 4 at or above 3,000 rpm and 210 imep was 5:10 hrs of which 3:10 hrs was at 3,300 rpm and 210 imep.

All layout drawings were complete except for a few checks. All details were complete except for a few small sheets, principally for gun synchronizer and camshaft accessory drives, fasteners, etc. GE final supercharger drawings had been received, materials specified and a parts list made. Final assembly drawing longitudinal section had been made and part numbers were being added. Additional assembly drawings and a bill of material in accordance with Air Corps requirements were being prepared. Van Dykes with above exceptions were submitted on 30 Oct 1934 to Wright Field. The remaining Van Dykes, including revisions, were expected to be submitted on 8 Nov 1938.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 76 – 78.]

2 Nov 1934. Prescott issued Memorandum Report E-57-285-8 reporting on a 30 Oct 1934 conference at MatCmd between Tilley, Prescott and Chenoweth about the O-1430-1 engine. Tilley brought Van Dykes and parts lists with the intention of delivering Contract W-535-AC-6322, Article 15, Item 1. He also brought a tabulation of drawings that had been checked and signed, drawings checked but not signed, drawings made but not checked, and a list of stud, bolt and small detail drawings not yet made. Continental wanted payment before 31 Oct 1934, the close of its fiscal year. A parts list was included but no numerical checking list, nor bill of material as called for in the contract. MatCmd stated that certification for payment could not be made while drawings were not accounted for. MatCmd wanted to cooperate, but receipt of a partial item was not sufficient basis for payment in full for that item, and no provision for partial payment existed for less than a complete item. Continental's request was refused.

It was found that the bill of materials called for in this item was included by error and should have been placed at the contract conclusion, and that this requirement could be modified by deviation at the written request of the contractor, and thus permit delivery of the item for payment when the drawings, parts lists and numerical lists were completed according to the contract terms. Questions concerning other contract items involving design and maintenance were also discussed. A letter from GE about the turbosupercharger and its installation on the engine was shown. MatCmd stated that this matter was not critical as it was not a factor in the acceptance and endurance tests, and required no action at the present time.

MatCmd preferred accurately ground supercharger drive gears, with backlash around 0.004", as experience indicated this to be satisfactory for the highly-loaded high-speed supercharger gearing.

Continental solicited MatCmd's material preferences for sealing ungasketed joints, and prevent corrosion of machined magnesium casting surfaces. Castor oil soap gasket compounds were generally satisfactory where gaskets were not used, especially if silk thread was used with them. Continental preferred aluminum foil covered gasket material and this was satisfactory to MatCmd.

MatCmd's engine maintenance and service liaison units were consulted on the question of safetying; safety-wire was preferable to cotter pins, lock washers or other devices. Palnuts were looked upon with disfavor because they were difficult to properly install without special wrenches. They also did not provide the degree of security offered by safety wire, especially when two or more safetied points were wired together, preventing studs, bolts, etc., from turning. Safety wire was readily available and easily adapted to all assembly situations.

Details of the fuel injector drive were discussed with the Carburetor Unit and questions of proper drive and injector lubrication were discussed. Continental was furnished a copy of a specification drawing covering the drive in question, which would enable completion of the drawing. The question of additional piston and ring development was also discussed. MatCmd stated that further thought would be given to this matter before any official action was taken regarding such tests. The present contract did not contemplate complete single-cylinder test termination with the three 50-hr tests on which reports were to be produced, and of which not one had yet been completed. The current tests were to constitute a minimum and serve as the basis for payment, but Continental was expected to continue the tests as needed to insure completion of the multi-cylinder tests with a minimum of cylinder, piston and ring trouble.

The status of the internally-cooled pistons loaned to Continental was discussed. While these pistons were expendable property, they should be accounted for by summarizing the endurance results obtained in a report, and eventually the pistons (or major portions thereof) were to be returned to MatCmd for credit and examination.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 73 – 75.]

6 Nov 1934. Prescott issued Memorandum Report E-57-285-9 reporting a 29 Oct 1934 conference at Continental attended by Tilley and Continental Vice President William R. Angell, and MatCmd Capt Powers and Prescott, about the O-1430-1 engine and single-cylinder tests, and the Hyper No. 1 Cylinder. Angell stated that Continental had every intention to continue developing the O-1430-1 and to manufacture it when development was complete. He further stated that Continental was completing its fiscal year on 31 Oct 1934 and would appreciate anything that could be done to accept the complete engine Van Dykes by that date. Tilley would hand-carry a complete set of Van Dykes, invoices, etc. However, when these were checked it was found that the list was incomplete and that acceptance could not be made until a complete list of detail drawings was submitted. Although MatCmd felt confident Continental would continue development.

Parts for the two Hyper No. 1 cylinders that were being fabricated on Purchase Order 35-644 were examined. The heads were partially machined, but an error had been made in machining one combustion chamber. Continental asked if the error was serious enough to cause rejection, and MatCmd replied that unless a Deviation was granted to permit acceptance of the head, the Air Corps Inspector would have no alternative but to reject as not conforming to the drawing. MatCmd suggested that all work on this head be delayed until such a deviation was allowed or refused, and that a sketch be furnished to show the exact departure from the drawing. A third casting was thought to be available and could be substituted. The loss to Continental would not be great, since only the casting, layout labor and spherical combustion chamber boring was involved. The cylinder barrels, jackets and connecting rod were also being fabricated.

The Hyper No. 2A cylinder was again being run on the last 50-hr run (3,300 rpm and 211 imep) in an attempt to complete this contractual item.

Because of limited time, single-cylinder testing could not be discussed in detail. Only a short run period had been accomplished on the current setup, the previous attempt having failed due to a stuck piston. This was a forged Lo-Ex piston with 0.027" skirt clearance, which was found to be considerably out-of-round. The failure cause was not determined, but it was pointed out that the piston design did not provide a stiffening ring at the open end. The test was continuing with a cast Lo-Ex piston having a circular strut.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 83 – 84.]

15 Nov 1934. Tilley released a progress report covering the period ending this date. The new piston, mentioned in the previous report, with American Hammered rings and inner rings was run in for 7:40 hrs to 3,000 rpm and 5 inHgG boost, after which the ring gaps had increased slightly. After 1 hr at 3,000 rpm and 211 imep, the gaps had increased by 0.015", 0.004", and 0.005", top to bottom. A new ring was placed in the 4th groove and a 1° bevel by 0.250" placed at the skirt top. After 10 minutes at 3,000 rpm and 210 imep the piston scored on the thrust side 45° toward the magneto. In view of satisfactory progress to this point, this unexpected failure was hard to explain.

A new piston was made to the same dimensions as the scored one except a 0.094" bevel drainage groove with vent holes was cut below the bottom ring and the skirt taper-round to give 0.026" clearance below the ring and 0.020" at the skirt bottom. The cylinder bore was reground 0.005" larger to clean it up. American Hammered rings were in short supply, so Perfect Circle rings were used to run-in the newly-ground bore. New bronze cones were placed on the flywheel as previous cones no longer fitted. After running in to 3,000 rpm and 6 inHgG boost, bad blow-by occurred; the top ring gap had increased by 0.055" and the others 0.011".

While continuing run-in at 13 inHgG and 3,000 rpm, gas appeared in the Prestone outlet line; the cylinder was leaking at the junction of barrel to head. The cylinder was being disassembled for further examination. Possibly the original assembly operation, which stripped threads and disassembly, which stripped more threads, the reduced section for the 0.063" oversize thread, and reassembly proved too much for this joint. Total time on this cylinder at or above 3,000 rpm and 210 imep was 6:20 hrs of which 3:10 hrs was at 3,300 rpm and 210 imep. This cylinder head had been on test for about 10 weeks, including six weeks at program start. A modified cylinder head casting had been received, inspected and partially machined.

All details, parts-lists and bill of material drawings were complete. Two final assembly drawings – longitudinal vertical section and transverse section through cylinders – had been completed. Three sections were in work – longitudinal horizontal, transverse through rear accessory drives and transverse through front accessory drives. These assemblies were to include all details and their part numbers. Van Dykes including the above assemblies were expected to be submitted to Wright Field on 28 Nov 1934.

An engineering analysis review of all piston and ring tests had been made. Given the number of tests started that terminated by piston scoring or ring wear, principally the top ring, some basic deficiency seemed to exist. The piston ring belt was out of contact with the wetted barrel for over half of a revolution. At the head-end was the joint; at the crank end the piston edge descended below the wetted surface, which might explain the high cylinder skirt temperatures. In order to reduce the test engine cooling deficiency the maximum feasible amount, a cylinder was under construction with the maximum amount of jacket. The effect on temperatures and ring wear can then be determined.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 80 – 82.]

1 Dec 1934. Tilley published a progress report covering the period ending this date. A new single-cylinder assembly with the head casting revised with a rib from the exhaust guide boss to the head between exhaust and intake ports, and a coolant jacket 0.75" longer than previous ones had been completed and was to be assembled to the test engine on 4 Dec. Another cylinder was being made to serve in reserve, thereby expediting tests. The test engine had been taken apart, reconditioned and reassembled. The coolant pump drive shaft was chrome plated where packing had reduced its diameter by 0.018". The crankshaft was reground under the hub cones and new bronze cones made. Thereafter, the flywheel ran true with 0.004" radial and 0.003" longitudinal indications. The oil cooling system was revised.

A complete Van Dykes set of assembly drawings, detail drawings, material specifications, parts lists and bill of material was delivered to MatCmd on 26 November. Comments on the engine support plate had been received from ALCOA, and comments on the ignition system had been solicited from the Breeze Corporation. Changes were being made to incorporate a modified vacuum pump oil circuit.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 86 – 87.]

13 Dec 1934. Prescott released Memorandum Report E-57-285-11 reporting on a 28 Nov 1934 conference with Long and Tilley, who delivered complete Van Dykes of the O-1430-1 engine, in fulfillment of Contract No. W-545-AC 6322 Article 15 Item 1. These were checked against numerical and parts lists. All drawings were delivered, checked, signed and released to active experimental files. Receiving reports were prepared and Continental received payment for the item.

Tilley stated that a new cylinder with a reinforced exhaust port wall, where previous failures had occurred, was being fabricated and would be ready for test in the near future. The Hyper No. 1 single-cylinder, on order for spark plug testing, was ready for delivery. Air Corps inspection of the component parts, along with assembly of the head, barrel and jacket, was accomplished on 26 November. Final inspection was to be made upon receipt at MatCmd.

The Aircraft Branch's request for modification to the O-1430-1 nose to conform to the proposed SAE No. 50 propeller shaft end was discussed. Since this proposal had not been adopted by the leading manufacturers, it was decided to postpone the suggested changes until the standard was adopted.

Continental submitted drawings of front and rear cones for use with the Government-loaned single-cylinder test engine in use for cylinder and piston development applicable to the O-1430-1 engine. These did not conform to SAE standards and Continental was to supply corrected prints for approval of the repair method used for the Government-provided engine used on W-535-AC-6422.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 88 – 89.]

15 Dec 1934. Tilley released a project report for the period ending this date. In order to keep the oil temperature below 175°F, the test engine oil coolers had been revised and the oil relief had been modified to discharge to the oil tank instead of the crankcase. The compression ratio was measured at 6.16:1. The cylinder with a cast Lo-Ex piston and American Hammered rings with expanders was run-in to 3,000 rpm and 14 inHgG boost, after which the ring gaps had increased by 0.006", 0", 0" and 0.004", top to bottom. After 1 hr at 3,000 rpm and 210 imep the top ring gap had increased by 0.008"; the others by none. The top ring was removed and the others moved up one groove; a new ring was placed in the bottom groove. A 40-min run at 3,000 rpm and 211 imep was stopped when the oil temperature exceeded 180°F. Ring gaps were unchanged but the top expander was flattened on one end. The expander ring was replaced by a new one and the oil cooler setup changed.

After a run of 1:55 hrs at 3,300 rpm and 216 imep ring gaps were unchanged but the top ring was tight in its groove due to carbon build up. The expander ring was again replaced and the engine run 5 hrs at 3,300 rpm and 211 imep; oil consumption was 0.55 gph. The ring gaps had increased so new ones were installed. The top ring was replaced by a plain ring without expander. This setup was run-in for 5 hrs and then 5 hrs more at 3,300 rpm and 211 imep; oil consumption was 0.19 gph. The top ring was pitted and the cylinder showed wear at the extremes of ring travel. No changes were made and the run was continued for 5:20 hrs when blow-by became excessive. The ring gaps had increased by 0.018", 0", 0" and 0.010", top to bottom, and the cylinder wear was sufficient to require bore regrind. Total time on this cylinder at 3,300 rpm and 211 imep was 17:55 hrs.

Drawings were changed to incorporate the revised vacuum pump oiling as outlined in the 2 Nov 1934 MatCmd letter. The stock list and test cylinder modification had been brought up-to-date. A listing of O-1430-1 fits and clearances has been started. Investigation of single-cylinder setup for connecting rod tests had been started.[USNARA RG342 RD1670, 502-108 O-1430 340630-341231. 91 – 93.]

31 Dec 1934. Tilley published a progress report covering the period through this date. The cylinder bore was reground to 5.510" diameter. A new Y-alloy piston was machined 0.039" top land, 0.047" ring land, 0.030" to 0.025" (taper ground) skirt clearances. After run-in the new setup was run for 9:05 hrs at 3,300 rpm and 211 imep. The cylinder bore was worn and the ring gaps had increased by 0.056", 0.019", 0.017" and 0.017", top to bottom.

The rings were replaced with new American Hammered rings of the same type. Mobiloil B (SAE 60) of the new solvent-treated type was used instead of the Stanavo 120 previously used. After a 5 hr run-in, the cylinder was run 10 hrs at 3,300 rpm and 211 imep. The cylinder bore head end had worn 0.016" and the ring gaps had increased by 0.017", 0.010", 0.010" and 0.010", top to bottom. During this run the blow-by had increased from 49 to 75 ft³/hr.

The cylinder bore was reground to 5.028". While running in the cylinder and its new piston and rings, the balance rod near the flywheel broke at 3,000 rpm. A previous balance rod set removed because of cracked bosses were reworked and installed. The engine was to be ready for continued testing by 7 Jan 1935. Total time on this cylinder at 3,300 rpm and 211 imep on 31 Dec 1934 was 39:50 hrs.

Test engine layout drawings showing alterations required to permit multi-cylinder engine connecting rod tests were complete. Re-listing of parts conforming to items of contracts W-535-AC-6322 and W-535-AC-6834 were nearly complete. Corrections for balance rods as a result of the test engine failure were being forwarded separately.[USNARA RG342 RD1670, 502-108 O-1430 350101-360219. 2 – 3.]

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