Continental XO-1430 Development
Part 10: 1 Jul 1937 to 31 Dec 1937
by Kimble D. McCutcheon
Published 7 Oct 2025

1 Jul 1937. Air Corps Inspector Robert Triggs reported that the XO-1430-1 assembly had started on 28 Jun 1937 but a machining error was discovered and a tear-down was necessary to correct the error. The engine was again assembled on 29 June and run-in. A 10 minute run was made at full power and load for MatCmd's civilian engineer Prescott's benefit, who pointed out that the engine's vibration was probably due to the dynamometer coupling's dynamic imbalance. This was being remedied before further running. Necessary crankcase changes were identified and foundry patterns were being updated. New castings were expected in about five days. The new camshaft housings were about 75% complete but were not to be assembled to the engine until the new crankcase was completed. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 140.

15 Jul 1937 Progress Report. The single-cylinder test engine was at MatCmd having its crankcase reworked.

A special arbor had been made to hold the XO-1430-1 dynamometer coupling during dynamic balancing by the Miller-Seldon Electric Company. The 6 in-oz out-of-balance condition was corrected and a compensator provided for the spark advance indicator to maintain coupling balance when assembled with the indicator in place. The engine was placed on the dynamometer and run for 3.5 hrs while total oil flow through the engine was measured. After a few readings, oil pressure dropped to about 75 psi and the oil flow was 139 lb/min, which was the pressure pump's capacity. Engine inspection revealed that the reduction gear back shaft front bearing was in poor condition, which probably explained the oil pressure loss and high oil flow; the reason for this failure was not obvious. The bearing was replaced, reduction gear journal reground, and the engine returned to the dynamometer for run-in and oil flow test continuation. As of 15 July 1937, XO-1430-1 total time was 323:10 hrs, time above 160 bmep was 30:24 hrs, endurance time was 25:32 hrs, time under power was 223:35 hrs, and time motoring was 99:35 hrs.

Corrosion Test: Metallurgical examination of cylinder barrel material samples with different protective coatings disclosed a slight increase in deterioration after 142 hrs in the ethylene glycol bath as compared with the condition during the previous inspection at 41 hrs. Total deterioration was slight, with no appreciable differences between the different protective coating samples.

Engineering: Continental planned to send crankcase drawings showing the proposed changes for MatCmd's approval. The revised cam housing and cover drawings were being mailed to MatCmd for approval. Replacement parts and Government liability to 15 Jul 1937 were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 155 – 158.

22 – 23 Jul 1937. Continental's J.W. Kinnucan and J. Hoven brought MatCmd two new crankcase castings, which were X-rayed and found acceptable except for a slight porosity in one lightly-loaded bearing diaphragm. MatCmd opined that this defect was not dangerous, so Continental was to finish machining the castings. Kinnucan asked about the single-cylinder test engine status and was told it was being prepared for shipment back to Continental. The crankcase had been delayed, but rebuilding was proceeding as rapidly as possible. MatCmd had noticed that the engine's oil passages were filled with sludge and suggested that some type of filter, such as the Skinner filter, be employed to trap sludge more effectively than metal screens.

Kinnucan requested that MatCmd initiate procurement authority to cover spare parts furnished through 1 Aug 1937; MatCmd replied that this would be initiated upon receipt of the spare parts list as of 1 Aug 1937. This order would not include the crankcase castings that were being machined but would include new cam boxes and covers fabricated by Continental. Kinnucan reported continued difficulty with connecting rod bearings having lead-bronze on the bearing shell inside and outside. MatCmd suggested a thin bearing liner in the blade rod working directly on the steel shell, the latter having lead-bronze only on its inner surface; apparently bearings with bearing metal only on one side worked well. Bearings purchased from the two sources of lead-bronze bearings differed little in wearing quality except that one bearing failed on the inside and the other on the outside. The difficulty appeared to be caused by the requirement of properly applying and quenching the lead-bronze to both sides of the steel shell.

Kinnucan stated that the current XO-1430-1 investigative focus was to determine the test stand vibration frequency. The dynamometer coupling alignment was to be checked, a rubber mount had replaced the solid mount, and the engine mount pedestal was to be reinforced to prevent longitudinal movement. If it were found that the vibration frequency matched the propeller shaft, a Thermoid coupling would be tried without the Fast coupling (both were used to connect the engine and water brake all together). Continental's test setup had only 8" – 10" between the Fast and Thermoid coupling, while MatCmd's had at least 3 feet. Continental had checked the coupling assembly balance and found it to be acceptable, but the vibration being experienced was too severe to proceed without some remedy.

Hoven described the corrosion tests being conducted by Continental to determine the best type of corrosion protection for the cylinder barrels. While several methods had been tested and appeared to vary significantly in their corrosion-inhibiting properties during the first few hours, after 25 – 50 hours exposure to hot Prestone, no method worked better than cadmium plating. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 30 Jul 1937 Memorandum Report E-57-285-65, XO-1430-1 Engine. 160 – 162.

29 Jul 1937. Triggs reported that before the last XO-1430-1 run-in on 16 July, it was necessary to remove 0.020" from the reduction gear idler gear journal to make it smooth enough for further running. This process removed the journal case hardening, raising doubt about whether the soft shaft would run correctly; inspection on 26 July revealed that the gear journal and its bushing were not running correctly. A new idler gear had been lapped to fit the original reduction gear set at the Farrel-Birmingham Company and was expected to arrive within a few days. The engine was being torn down and a new set of Allison connecting rod bearings was being installed. Continental had ordered a complete set of Allison bushings for the engine front end, and these would be installed before any further endurance running occurred. The two new cam housings were to be completed within the week and would be ready for installation with the new crankcase. These parts had not been completed in time to be listed in Continental's 15 Jul 1937 Progress Report. Two crews working 20 hrs per day were making rapid progress machining the new crankcase. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 159.]

31 Jul 1937 Progress Report. The single-cylinder dynamometer setup was repaired and improved. The dynamometer was cleaned, balanced and calibrated. The thermometers were calibrated and the fuel system cleaned and inspected. MatCmd had not yet returned the test engine.

The XO-1430-1 was run-in for 4.5 hrs to 3,000 rpm and 0 inHgG. Inspection showed that the soft idler gear journal had not worn well; it had been reground after the previous run, leaving the journal hardness at about 200 Brinnell. A new idler gear was on order from Farrel-Birmingham. New Allison connecting rod bearings with harder bronze on the inside were installed and would be run as soon as the reduction gear was assembled. The oil pump was run separately to obtain flow data with changing oil temperature; this data was inconsistent and the tests had to be repeated. New crankcase castings had been received, rough-machined, X-rayed at MatCmd and accepted for finish machining. The crankcase was expected to be complete on 23 August. As of 31 Jul 1937, XO-1430-1 had run 327:15 hrs total, 30:24 hrs above 160 bmep, 25:32 hrs endurance, 226:45 under power and 100:30 motoring.

Corrosion Test: The corrosion test setup was moved to another location with provisions for checking the Preston pH value. No new samples were tested during this period.

Engineering Changes: Crankcase drawing changes had been completed and reviewed; revised drawings were to be forwarded to MatCmd for formal approval. Replacement parts and Government Liability were attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 163 – 170.]

5 Aug 1937. Triggs reported that no XO-1430-1 running had been done during the week. The reduction gear housing was being rebushed to fit the new idler gear, which was in stock. All pistons were being fitted with new piston ring pins that all had the same drive fit and were to be interchangeable. Heretofore there had been variation in the pin fit, which may have caused so many failures. The pin usage was conducive to satisfactory piston ring performance and Continental intended to continue using them if possible. Continental expected to have the engine ready for further testing during the following week. During this upcoming run, the vibration characteristics were to be monitored using a method suggested by Prescott. Oil pump tests with the pump detached from the engine were being conducted to determine the cause of inconsistent oil flow at higher temperatures. The two new crankcase halves were to be bolted together and final machining of the main bearing saddles, etc., was to be started. A new lead-bronze main bearing set had been received from Bohn Aluminum Company; they were found to contain considerable porosity and would probably be rejected. The silver-cadmium main bearings now in the engine were satisfactory for further use. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 171.

13 Aug 1937. Triggs reported that the XO-1430-1 had been assembled with the following new parts: piston compression rings, piston ring pins, reduction gear idler, and reduction gear idler bushings. Continental had intended to run the engine on 13 August, but when the reduction gear was being assembled it was discovered that the reduction gear pinion pilot on the propeller shaft was slightly undersize. The reason for this was unknown, but this pilot must have been ground smaller at some point without Triggs' knowledge. The shaft was checked dimensionally both at Continental and MatCmd before acceptance. In order to prevent the gear from getting off-center the propeller shaft pilot was being chrome-plated 0.006" and ground to fit the gear. The engine was expected to be ready to run on 16 August. The remote oil pump tests had been completed. Curves showing the test results had been prepared. Further tests were planned with the pump installed on the engine, and a report covering all tests would be forwarded to MatCmd after completion. Work on the new crankcase was proceeding; it was about 85% complete. Allison connecting rod bearings were also installed. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 172.

P10Fig01	P10Fig02

15 Aug 1937 Progress Report. The single-cylinder test engine was still at MatCmd; its dynamometer was ready for immediate engine installation when it was received.

Because of delays in reduction gear parts fabrication, the XO-1430-1 was not run during this period. All piston ring pins were removed and reassembled with a carefully selected fit. The ring pins in the second groove were moved to the thrust plane, allowing a minimum of angular movement, resulting in less force on the locating pins. All pistons got new compression rings as some were slightly worn. Work on the new crankcase had proceeded rapidly, with all machining expected to be complete on 19 August. The crankcase was expected to be ready for assembly not later than 23 August.

During this period the oil pump was run separately to obtain flow data at various oil temperatures and with various intake oil pipe line sizes. The attached curve sheets show the results of these test runs. A restriction in the pressure pump inlet line was clearly shown in P10Fig01, and as a result of this test the size of all oil-in lines on the test setup were increased from 1.0" diameter to 1.5" diameter. P10Fig02 showed the effect of oil temperature on pump performance and at 3,440 rpm pump speed, which corresponded to 3,000 crankshaft rpm. The pump delivery was 127 lb/min, which gave a pump volumetric efficiency if about 90%. It was apparent that no difficulty would be experienced with the pump operating at 190°F. A special motor was equipped with a rotating disk and tachometer to record vibration data that all hoped would identify a vibration source. XO-1430-1 run time was 327:15 hrs total, 30:27 hrs time above 160 bmep, 25:32 hrs endurance time, 226:45 hrs under power and 100:30 hrs motoring.

Engineering: Routine drawing changes continued. No additional replacement parts were required during this period, but a recapitulation was attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 178 – 182.

20 Aug 1937. Triggs reported that XO-1430-1 propeller shaft pilot repair had delayed assembly for six days due to poor management. The shaft was sent outside to have the pilot chrome plated and due to the lack of proper instructions the magnesium oil plug inside the shaft was ruined by the cleaning acid. In order to remove the oil plug it was necessary to bore out a good bushing from the shaft end. The oil plug was replaced with one from an old shaft and the bushing was replaced with a new one from Allison. The propeller shaft was heat treated at 300°F for 10 hrs to neutralize the plating effects (hydrogen embrittlement) as much as possible. The engine was finally assembled on 19 August and was being run-in on 20 August. Oil flow tests and a vibration frequency check were planned. Machining on the new crankcase was complete and it was being inspected. Engine assembly with the new crankcase and cam housings was to be started immediately after completion of these tests. Allison main bearings were to be used in the new crankcase. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 173.

24 Aug 1937. Triggs reported that XO-1430-1 run-in was completed on 20 Aug 1937. During this run-in an attempt was made to determine the vibration frequency that had been noted in the engine. The apparatus used for this check was found to be out of balance and unfit for use. The new crankcase was completed and accepted on 20 August and it was decided to abandon further tests and concentrate on engine assembly with the new crankcase. In the meantime the vibration test apparatus was being balanced and prepared for use. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 175.

30 Aug 1937. Triggs reported that the XO-1430-1 assembly with new crankcase, main bearings and camshaft housings was completed on 30 August. The engine was being mounted on the test stand for run-in of the new parts. If this run-in was satisfactory, a 10-min run at rated power and speed was to be made before inspection. Endurance running was to commence during the week. Triggs had been informed that two running crews would be available. The vibration frequency checking apparatus had been balanced and another attempt was planned for the next run. During the last tear-down an accessory drive shaft bushing was slightly scored; it had been replaced by a new one. No failure cause had been determined. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 176.

31 Aug 1937 Progress Report. The single-cylinder test engine was still at MatCmd, but the test setup was ready for immediate engine installation when the engine was received.

The XO-1430-1 was assembled with the old, slightly cracked, crankcase, new piston rings and ring pins, and the original reduction gear set except for the pinion with the vibration damper. After a 6.5 hr run-in, inspection showed all the rings in perfect condition and all the piston rings in place. However, the eccentric bushing was slightly scored. When the new crankcase was complete, the engine was assembled with the new crankcase, all new Allison main bearings, new Allison connecting rod bearings, and new cam housings.

After a 7.5-hr run-in, the engine was operated at full throttle for 10 minutes during which the boost was 18 inHgG and the observed output 980 bhp. This relatively poor performance was attributed to the damaged supercharger impeller, which resulted from when the nose lock pin broke and fell into the impeller entrance. The impeller was to be compared and testing continued.

The engine vibration amplitude was materially decreased, which may have been due to the stiffer crankcase allowing less distortion from the primary internal couples. Attempts were made to obtain vibration frequency records by using a stylus bearing on a piece of waxed paper revolving on a flat disk. Difficulty was encountered in getting reliable records due to the stylus itself contributing to the vibration. XO-1430-1 time was 340:09 hrs total, 30:36 hrs time above 160 bmep, 26:32 endurance time, 237:07 time under power and 103:02 motoring.

Corrosion Tests: Since 16 Jun 1938 until 31 August, the XO-1430-1 was run a total of 24:39 hrs, of which less than 15 minutes was at high output; the ethylene glycol was strongly acidic (4.4 pH). New ethylene glycol had a pH value of 9.0 and the ethylene glycol used for 100 hours in the corrosion test setup showed a 4.5 pH value.

Engineering: Studies were being made to provide a new method of locating the engine front to ensure proper alignment of all gear centers. Replacement parts and total Government liability as of 31 Aug 1937 was attached. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 183 – 190.

Harold E. Morehouse's Accessory Drive Patent (US 2,051,568)

3 Sep 1937. Triggs reported that on 31 Aug 1937, the XO-1430-1 was run for 5 hrs, after which a run of about 30 minutes at 3,000 rpm and 750 hp, followed by a 10 minute run at full speed and power. Subsequent inspection revealed that the accessory drive shaft front crankcase eccentric bushing had seized. A very careful study suggested that insufficient front crankcase bushing clearance, combined with accessory shaft and reduction gear housing misalignment had caused the failure. Adjustments were planned to remedy this trouble and the engine was expected to again be running early next week. The vibration frequency checking apparatus was tried. The cards obtained showed a frequency considerably above the engine speed and it was believed that the pointer used gave false readings and would have to be redesigned. However, the fact is that after installation of the new crankcase engine vibration decreased to the point that it was negligible; Triggs opined the vibration would not interfere with satisfactory engine performance. Curves showing the remote oil pump performance had been included in the 15 Aug 1937 Progress Report. Oil pump flow tests with the pump mounted on the engine ware planned. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 177.]

13 Sep 1937. Triggs reported that the XO-1430-1 repairs had been completed on 7 September and after a 4-hr run-in, a 10 minute run was made at 3,000 rpm and 850 hp. The reduction gear was torn down and found to be in excellent condition. The Dwg # 503549 and Dwg # 503655 camshaft drive gears were considerably worn and were to be replaced at the next complete tear-down.

On 9 Sep 1937, an endurance run attempt was made but spark plug trouble was encountered for the entire day. An oscillograph was attached to the engine in another effort to check the vibration frequency. On 10 Sep 1937 the spark plug trouble was cleared up and the engine was run at 3,000 rpm and 400 hp; it was immediately noted that the vibration had returned and was as bad as ever. Oscillograph readings were taken with the voice coil pick-up mounted first at the engine mount plate rear and then at the mount plate front. Readings showed a 7,800 rpm frequency and every fifth peak showed approximately 20% higher amplitudes than the rest. The accessory drive shaft speed was 7,500 rpm when the crankshaft speed was 3,000 rpm. In order to determine whether the accessory drive shaft was a vibration source the engine was motored at various speeds with the quill shaft removed so that only the accessory drive shaft, camshaft and reduction gears were turning. Vibration of lower amplitude but at considerably higher frequency was noted, especially at 3,000 rpm. The frequency record was 14,400 Hz with every third peak higher. On 4 September the engine was to be run under its own power with the mounting frequency changes by revising the rubber mounting. This will determine the effect of mounting on the vibration. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 193.

16 Sep 1937. Triggs reported that the XO-1430-1 was run on 14 September with the rubber mounting bolted down tight on both sides; previous to the run the ignition was carefully checked and a cracked distributor cap was found. This was replaced and the engine ran smoothly. The rubber mount on one side was then released and the engine still ran smoothly. Continental decided to run a 5-hr endurance test, but spark plug trouble was encountered and full power and load running was abandoned until 16 September. During the night the oil level in the cam housing was changed and made slightly higher in order to better lubricate the exhaust valve stems. When the engine was started on 15 September the distributors were 180° out of time and gasoline in the exhaust tunnel exploded, wrecking the outside exhaust stack. This was replaced in about three hours.

The engine was then started on an endurance run but the Bendix spark plugs immediately failed; they were replaced with Champion mica plugs. The engine was again started on an endurance run and ran very smoothly at full power and load for about 10 minutes; the power suddenly fell off and the engine was shut down and removed from the stand for inspection, which revealed that the #1 connecting rod had seized on the crankpin. The crankpin was scored, but could probably be reground; the No. 1 connecting rods would probably have to be replaced with a new one from stock. No failure cause was determined. One-half of a reduction gear tooth was broken from the Dwg #503559 reduction gear but this did not damage any other parts. The gear failure cause was undetermined, but Continental's Metallurgical Department planned to study the failure. A replacement reduction gear was in stock, no other damage was found, and further engine running was dependent on regrinding the No. 1 crankpin. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 194.

17 – 18 Sep 1937. Kinnucan met with Prescott at MatCmd and brought the XO-1430-1 crankshaft with the damaged No. 1 crankpin, which had been damaged by a connecting rod bearing failure that was inadequately explained. It appeared that the bearing shell seized on the crankshaft and turned in the rod, shearing the dowel pin; the bearing loosened, as evidence by the 100-lb drop on the dynamometer scale, followed by recovery. The engine was immediately shut down; it was found that the crankshaft and connecting rod damage could be fixed by regrinding the crankpin and setting a new underside bearing liner in the connecting rods. The crankshaft was magnafluxed, and no defects were found in the No. 1 crankpin. However, a small defect was discovered in the No. 4 main bearing, which appeared to be a forging defect rather than a fatigue crack. This defect consisted of a longitudinal line probably not reaching the bearing surface, and the indication was that it was a small air pocket or slag inclusion that was not attributable in any way to the crankshaft use. MatCmd opined that these defects were of no consequence and that the crankshaft was suitable for further use.

Kinnucan transported the crankshaft to Cleveland, Ohio where it was to be reground by the Ohio Crankshaft Company. He predicted that the XO-1430-1 would be ready to continue tests by 23 September. Kinnucan said that engine vibration tests indicated that the peculiar troublesome vibration was probably due to the rubber mounts that had been installed under the engine bearers, and that removing the rubber from one engine bearer practically eliminated the vibration. The device for studying this vibration was an electromagnetic pickup fashioned from a loudspeaker voice coil and magnet. This pickup's output was observed using an oscilloscope that gave a velocity rather than a displacement indication. In these records, higher frequencies were very predominant while the troublesome frequencies appeared to be first order and half order. MatCmd personnel pointed out that the velocity pickup did not give a constant amplitude for specific frequencies and suggested that an integrating circuit consisting of a resistor and capacitor, such as was used with the MIT torsiometer, be inserted between the magnetic pickup and its amplifier. Kinnucan stated that this would be incorporated into the experimental setup.

Kinnucan said that several supercharger impeller nut pin failures had occurred. The broken pin pieces came through the supercharger and damaged the impeller vanes. MatCmd replied that the only know method for preventing this trouble was to drill the pin hole slightly undersize and drive a wire nail tightly into the hole, after which the ends were bent over into slots provided in the impeller nut.

Kinnucan brought reduction gear parts with a damaged gear tooth that had presumably failed during the connecting rod bearing failure. These parts were all magnafluxed and no fatigue cracks were observed; however, the broken tooth surroundings exhibited greater than normal bearing pressure. This may have indicated a tight spot in the gear mesh since this gear had been manufactured to operate with another pinion and had been hand-lapped by Farrel-Birmingham Company to work with the current pinion. The gear had operated only 5 hrs at full load while the previous gear was in excellent condition after more than 20 hrs at rated power. MatCmd directed Continental to photograph the gear failure and send the broken parts to Farrell-Birmingham for examination.

The connecting rod bearing failure cause remained a mystery; Kinnucan said that it was uncertain whether the bearing had sufficient end clearance and that Continental would investigate in order to avoid a similar failure in the future. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 205 – 207.

23 Sep 1937. Triggs reported that the damaged XO-1430-1 crankshaft, after having inspected at MatCmd, was sent to the Ohio Crankshaft Company in Cleveland, Ohio, for repair. The shaft was sprung 0.018" but was straightened as perfectly as possible before any grinding was done. The damaged crankpin was cleaned up by removing 0.017" and a new rod pair was machined to fit. Main bearing journals 1, 2, 3, 4 and 7 were trued by grinding off 0.009"; the other journals were not touched as only five new main bearing shell sets were available. The connecting rods were all checked for weave and none were found off more than 0.015" at the rod upper end in a full revolution. It was not known whether this condition had existed before the connecting rod failure. All connecting rod bearings had an extra oil hole drilled at the point of maximum loading and two were prepared with an additional connecting groove in an effort to prevent further failures.

The engine was assembled with two new Dwg #503549 and Dwg #503655 camshaft drive gears. During this shutdown the oil intake line size to the pressure pump was increased to 1.75". Heretofore it had been necessary to boost the intake oil with an auxiliary pump and this expedient was expected to be eliminated. In an effort to prevent preignition and other spark plug trouble previously encountered, a small air manifold was setup inside the mount plates to blow compressed air on the spark plugs. Electric fans had proven ineffective for this purpose. The XO-1430-1 was expected to be ready on 27 Sep 1937. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 195.

28 Sep 1937. Triggs reported that XO-1430-1 assembly was delayed because two reduction gears did not run together properly and had to be returned to Farrel-Birmingham Company to be lapped. Assembly was completed during the evening of 27 September and the engine was being run-in on 28 September. When run-in was complete the engine would be torn down for inspection. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 208.

1 Oct 1937. Triggs reported that the XO-1430-1 was run for 5 hrs on 29 September. Some oil flow tests were being run at 400 bhp and 3,000 rpm when a slight load drop of about 30 lb was noted. The test engineers decided something was wrong although there was no oil pressure drop. Further inspection revealed that the No. 2 connecting rod bearing had failed. The outer bronze had broken into small flakes but there was no evidence of extensive heat. The damaged parts were to be brought to MatCmd at a later date. Test engineers planned to assemble the engine with a new crankshaft and the original Bohn Aluminum connecting rod bearings; the old crankshaft was to be sent to the Ohio Crankshaft Company for necessary repairs. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 209.

6 Oct 1937. Prescott met with Tilley and Kinnucan at MatCmd and brought with them a full rod bearing set from the XO-1430-1, including both failed rod bearings, which showed evidence of primary outer bronze facing failure, which would naturally be followed by oil pressure loss on the inner bronze, also destroyed; in both cases the crankpin was damaged. Kinnucan stated first that the shaft would not be straightened, but merely reground sufficiently undersize to clean up the bearings and make them run true. However, after discussion, Continental concluded that less harm would come from straightening the shaft than from grinding the journals as much as 0.050" undersize. It was therefore decided that the shaft would be straightened and the damaged bearing reground so that engine operation could resume using this crankshaft. It was further decided that the previous decision to use the spare crankshaft at this time would not be followed and the spare crankshaft would be kept in stock until the present crankshaft was damaged beyond repair.

Kinnucan stated that the new crankshaft was equipped with oil plugs made from steel tubes and had been tested with kerosene under pressure; these tubes were very much more satisfactory than the previous cast magnesium oil plugs. An alternate design incorporating moulded rubber rings for positive seal had also been tested, but that the steel sleeves were satisfactory, less expensive and easier to install.

New connecting rod bearings were on order from the Allison Engineering Company and from the Bohn Aluminum and Brass Corporation. Allison had promised delivery in about two weeks. On this basis it was at first proposed that the spare crankshaft and a set of used Bohn bearings that were still in good condition be used to continue testing. However, further discussion revealed that all bearings in then in use had clearances on the high side. It was determined that the two failed bearings had clearances between 0.005" and 0.006" while the other bearing clearances were 0.004" to 0.005". MatCmd's previous experience with copper-lead bearings had determined that proper clearance was around 0.0008" per inch of journal diameter, which meant that a 3" crankpin should have a 0.0025" clearance. On this basis it was decided that the engine would be setup with new Allison bearings as soon as they were received and that the Nos. 1, 2 and 3 crankpin clearances would be 0.0025", 0.0035" and 0.0045", while the clearances between the bearing shell and blade rod would be 0.002", 0.003" and 0.004". Crankpins 4, 5 and 6 were to be equipped with bearings having the same clearances, but with a different bronze composition with a harder structure than that contemplated for crankpins 1, 2 and 3.

In connection with the failed outer bronze surfaces, Kinnucan showed the disintegrated material that had been found in the engine after the bearing failure. The peculiar bronze that had been used had flaked, producing flakes from the size of sand particles up to 0.25" in diameter. The softer bronzes previously used for the bearing outer surfaces did not cause disastrous failures but developed small spots that gradually grew larger as the engine was operated. It appeared that the bearing metal pitting was due to hydraulic action of oil being forced into the bearing pores when the surface was under high pressure due to action of the journal moving over heavily-loaded bearing areas. This condition was aggravated by excessive bearing clearance since the effective bearing portion in contact was greatly reduced by radii differences in the inner and outer bearing surfaces. It was therefore reasoned that decreasing the clearance on these bearings would also decrease the bearing's tendency to disintegrate because the load would be distributed over a much greater area.

Kinnucan stated that the bearings on order from Bohn had two or three different metal compositions, and that there was no real difference between the Allison and Bohn bearings. Prescott opined that once the correct clearance was established the bearing problems would be solved. No further XO-1430-1 running would occur until better rod bearings had been obtained and proper clearances established.

Kinnucan suggested a test rig comprising a fabricated steel crankcase, a radial engine crankshaft adapted to the correct stroke, two used cylinders and two used pistons to get preliminary rod bearing information. MatCmd wanted to grow this concept into a complete 2-cylinder test engine. Kinnucan promised to study this further. On the subject of test engines, the single-cylinder test engine previously mentioned had apparently made its way back to Continental after being upgraded by MatCmd. However, MatCmd announced that it would need the test engine back around March 1938. Tilley stated that the test engine, as received from MatCmd, had required work before being ready to resume testing; the balancing connecting rods' Babbitt was in bad condition and the rods had been sent out to have the Babbitt replaced. MatCmd stated that the newer design incorporated thin, steel-backed lead-bronze bearings to eliminate having the Babbitt replaced. Since the present rods had already been reworked, MatCmd decided to delay this change.

Tilley asked whether MatCmd would financially back a further single-cylinder test program; MatCmd did not think such a program was warranted until the XO-1430-1 development test was nearer a successful completion. However, Tilley was asked to submit a single- or twin-cylinder test program proposal in order to determine the best conditions for economical cruising operation on Grade 100 fuel. Pistons with 7.75:1 compression ratios had already been built and were on hand at Wright Field and Continental. Tilley agreed to submit such a proposal. [USNARA RG342 P03. 11 Oct 1937 Memorandum Report E-57-285-67, Conference with Messrs. Tilley and Kinnucan of the Continental Motors Corporation, Detroit, Michigan, on XO-1430-1 Engine, October 6, 1937.]

8 Oct 1937. Triggs reported that the XO-1430-1 was ready for assembly with a new crankshaft. Assembly start depended on receipt of the new connecting rod bearings from Allison Engine Company. Delivery of these parts had been promised for 15 October. These bearings were to be tested in accordance with the method MatCmd had recommended during a recent conference. [RG342 RD1676 503-106 O-1430 Vol. 2 370101-371008. 210.

Continental XO-1430-1 Progress Reports and Air Corps Inspector Reports ended on 8 Oct 1937 and resumed on 21 Jun 1939. The author has been unable to locate these in the Engineering Division Files held by the U.S. National Archives at College Park, Maryland. However, among the Power Plant Laboratory Microfilmed Memorandum Reports, the author found a few other contact accounts, which provide our only visibility into XO-1430-1 development during this time period.

8 Oct 1937. Kinnucan telephoned Prescott to report that the Ohio Crankshaft Company had examined the damaged crankshaft and determined that the damaged crankpin had spots that were harden by the heat during the bearing failure; these spots were considerably harder than the original crankshaft, which presented a dangerous condition that might lead to crack development between the hard and soft spots. Continental decided to repair the damaged crankshaft, but to retain it as a spare and use another crankshaft that was in stock. The new crankshaft was to be installed with modified connecting rod bearings so that XO-1430-1 testing could resume. Kinnucan stated that the next bearing setup would use the original B-28 metal on the inside and the outside metal would have a hardness about half way between the inside metal and the old hard outside metal that had flaked away. The second bearing set would be lined with B-325 metal with an outside composition the same as for the first bearing set. This outside metal would contain about 6% tin, making it somewhat harder than the soft metal and yet avoid the danger of repeating the two connecting rod failures. This decision to use the new crankshaft was at variance with the decision reached during Kinnucan's 6 Oct 1937 MatCmd visit, reported in Memorandum Report E-57-285-67 dated 11 Oct 1937. [USNARA RG342 P031128. 11 Oct 1937 Memorandum Report E-57-285-68, Telephone Conversation with Mr. J.W. Kinnucan of Continental Motors Corporation on XO-1430-1 Engine Crankshaft.]

15 – 16 Oct 1937. Prescott, Kinnucan and G.A. Zink of Allison Engineering Company met at Wright Field to discuss two XO-1430-1 connecting rod bearing failures. Kinnucan stated that these failures appeared to have begun when Continental followed Zink's bearing clearance recommendations. Bearing and assembly record examination revealed that the failed bearings all had the large bearing clearances Zink while the successful bearings had slightly smaller clearances. Because of these findings, the XO-1430-1 had recently been set up with a range bearing clearance range that MatCmd had found satisfactory during oiling system tests on a V-type engine with unit bearing loads 50% higher than the XO-1430-1. The objection to this was that if a bearing failure led to a connecting rod failure the only available XO-1430-1 would be wrecked and MatCmd might not have the funds for another engine. It was therefore decided to rebuild the engine using the old, repaired crankshaft and the old, cracked crankcase. The intent of this rig was to subject the connecting rods whose bearings had previously failed after they had been reground to accept oversize bearings with proper bearing clearances. It was planned to use the bearing clearances established at a previous conference on three crankpins, with the other three fitted with other bearing setups. Thus, various connecting rod installations could be tested without further endangering the crankcase or crankshaft that would be run during the 50-hr endurance tests.

Kinnucan said that three experimental bearing types had been promised by Bohn Aluminum and Brass Corporation in about three weeks. Allison could furnish the same bearing metals as previously used in about ten days. Zink stated that after evolving the most satisfactory method of lubricating these bearings that very little trouble was being experienced with V-1710 engine, although there had been cases where the outer bearing metal flaked off in a manner similar to the XO-1430-1. Kinnucan stated that whatever bearing set was received first would be tested in order to proceed as rapidly as possible. He pointed out that a complete main bearing set would be required as the crankshaft main journals were now slightly undersize. Kinnucan agreed to proceed along these lines in order to determine the correct bearing clearances and lubrication conditions. [USNARA RG342 P031124. 20 Oct 1937 Memorandum Report E-57-285-69, Conference with Representatives of Continental Motors Corp., and Allison Engineering Company on XO-1430-1 Engine Bearing Failures.]

Diagrams Helpful in Understanding the Connecting Rod Failures

13 Dec 1937. Prescott visited Continental to examine the various main and connecting rod bearings that had been used in the XO-1430-1. Those supplied by Bohn Aluminum were in exceptionally good condition and promised to give satisfactory service life. The Allison No. 1 connecting rod bearing outside high-tin lead-bronze coating appeared to have initially failed. Once this bearing metal disintegrated it left about 0.063" of lost motion between the connecting rod bearing and blade rod. The shock due to this lost motion appeared to have caused a blade connecting rod bolt to break, and the other bolt immediately failed in bending, throwing the blade rod out through the crankcase side; fortunately, no damage other than to the previously-discarded crankcase, one cylinder barrel and one piston occurred. This was the forth Allison connecting rod bearing outer-bronze failure; in all cases the outer bronze disintegrated in flakes and that failure occurred suddenly and with no apparent reason. This was the second failure on the No. 1 crankpin; the other failures having occurred on the Nos. 2 and 3 crankpins.

This latest failure occurred when the engine was running under light load at only 1,600 rpm; there was no apparent lead loss and no knock prior to the failure. It was concluded that the bearing metal had previously failed and when the engine was operating at 1,600 rpm the connecting rod loads were chiefly centrifugal with gas load reversals very light. This explained the absence of knock before the failure. Examination of the crankcase and rear accessory housing showed that the bearing metal had been out of the bearing long enough to be flushed out of the crankcase and into the rear sump. The blade rod and connecting rod steel backing conditions further indicated the engine had operated for a period after the bearing metal had disappeared.

Based on the testing that had been done and the failures experienced, it was decided to install a complete Bohn bearing set for future running. These bearings had a small tin percentage, which made the alloy slightly harder than pure 70-30% copper-lead bronze. Testing with this bearing metal suggested superior results to previous tests where a certain amount small spots of bearing metal had flaked out.

The XO-1430-1 was to be assembled with the latest crankcase and a new crankshaft. A main bearing set previously used with this crankcase was to be reinstalled. Connecting rod bearings would be set up according to the following schedule:

Since one cylinder barrel had been lost, it was agreed that a new cylinder assembly incorporating an alloy steel cylinder barrel would be installed. It was believed that previous alloy steel wear failure had been due to the barrels being ground straight when cold. With the present process, carbon steel barrels were ground with the cylinders heated in hot oil so they were approximately straight under normal operating conditions; previous cold-ground cylinders had irregular bores with as much as 0.008" taper when hot, necessitating piston ring gaps opening and closing up to 0.025". This was thought responsible for the erratic blow-by and for the extreme wear with cold-ground cylinders. One new connecting rod assembly was to be used, and one new piston. The 1R piston was slightly scratched by bearing metal particles thrown into the cylinder when the bearing failed. However, slight hand-stoning was expected to make the piston again serviceable. The old crankshaft, on which four connecting rod failures had occurred, was thought unsafe for continued running.

Continental was preparing a new spare crankshaft that would make use of revised main and crankpin journal oil plugs consisting that were short steel tubes, inserted by hand and retained by steel clevis pins and cotter pins. Tests with kerosene had shown this scheme to be satisfactory since the tubes and crankshaft coefficients of thermal expansion were identical. Continental was also preparing a new spare crankcase since testing had proved the changes that made it stiffer had been effective. [USNARA RG342 P031121. 17 Dec 1937 Memorandum Report E-57-285-70, Visit of Mr. F.L. Prescott to Continental Motors Corp. on December 13, 1937, Regarding the XO-1430-1 Engine.]

30 Dec 1937. Prescott traveled to Continental where Tilley said that the flexible connection between the carburetor and engine had been eliminated. A vibration investigation had identified deflection in the mount plate web section at the engine rear. A stiffening scheme using braces attached to the engine was proposed, and since the only impact on the engine was longer studs through the rear-most bearing diaphragm, it was being implemented.

Tilley reported that the front accessory was being redesigned to eliminate alignment difficulties during engine assembly. Work on a hydraulic propeller control that incorporated the latest Air Corps requirements for governor connections and oil passages within the propeller shaft was also under way. MatCmd had stated that the most satisfactory method of sealing the propeller oil connection was by means of a piston ring seal running in a hardened steel sleeve, and that there was a requirement to provide a two-way pressure supply through the propeller shaft to the propeller control mechanism.

After the XO-1430-1 had operated for several hours, a tear-down inspection revealed that the bearings were in satisfactory condition, although it did appear that the crankpin bearings with no grooves were in better condition than those in which grooves were machined. The engine operating period had been too short to verify the superiority of the ungrooved bearings. The alloy steel cylinder barrel was still not ready for installation on the engine. The Champion M-11 spark plugs had been breaking down at the crimp point at the shell top. When they flashed over at this point, the plug fouled; BG-157 spark plugs were being used in the XO-1430-1. [USNARA RG342 P031118. 10 Jan 1938 Memorandum Report E-57-285-72, Conference on December 30, 1937, with Mr. N.W. Tilley of Continental Motors Corp., Detroit, Michigan on XO-1430-1 Engine.]

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