From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Investigation into Bentley piston seizures, detailing boiling tests and subsequent modifications to address cooling issues.
| Identifier | ExFiles\Box 87\2\ scan0052 | |
| Date | 17th April 1935 | |
| FILES. X236 17.4.35. BENTLEY PISTON SEIZURES. ------------------- We have recently been investigating the seizing up troubles experienced on Bentley, but so far have not been able to reproduce the trouble. It must be stated at the outset that the unit upon which these tests were carried out had previously done a considerable amount of running, so that the cylinder bores, although not oversize in any way, were thoroughly "run in", the main bearings had also done a considerable amount of running and were passing far more oil than those of a new unit, so that once the oil had reached the main bearings, the cylinders were always well lubricated due to the excessive amount of oil thrown from the bearings. The unit was fitted for these tests with a standard set of E.B.1299 pistons that had done a little running in another unit, and no attempt was made to give them any "running in" when put in the test unit. Boiling Tests. Our first test consisted of running the engine with the cooling water boiling and altogether the engine was run approximately 5 hours at various speeds and throttle positions with the engine boiling, but without seizing a piston. We had trouble at this stage with Nos. 5 & 6 exhaust valves seizing; in fact with the engine running at 2500 r.p.m. and water inlet temperature at 100°C., we could only run for approximately 3 to 5 minutes before one or both of these exhaust valves seized. This trouble we attributed to the fact that efficiency of the water pump is reduced so much with the inlet water boiling that water holes at the front of the cylinder head are more than sufficient to pass the water delivered so that the rear of the cylinder block and head had no water flow and steam pockets were no doubt formed. We partly overcame this trouble by blanking off seven of the water holes at the front of the cylinder head, thus causing the water to pour from the front of the cylinder block to the rear before entering the cylinder head. We left one water hole open to each of the front cylinders in order to relieve any steam pockets that may have formed. After this modification we had only one exhaust valve seizure and this was No.2, which seized after the engine had been boiling furiously for 25 minutes at 2500 r.p.m. | ||