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).
Despatching experimental Bentley pistons with American type rings to fix oil consumption issues.
| Identifier | ExFiles\Box 146\2\ scan0326 | |
| Date | 7th August 1937 | |
| W/P. To Sr/VA. from Rm{William Robotham - Chief Engineer}/Mths.{Reg Matthews} BENTLEY OIL CONSUMPTION. We are despatching this week-end a set of the latest type Bentley pistons to which we have fitted a set of American type rings. We are sending these for you to try in a customer's engine on which all our recommendations have failed to produce a satisfactory oil consumption. You will note that these rings have a very high pressure and should only be used on chassis fitted with large oil pump and on a car that is driven in a fast manner, so that the cylinders will always be well supplied with oil. These pistons have purely been sent out for an experiment and we cannot supply further sets, our own experience being that we are too near the border line of seizing. Our investigations on bore wear at present show that ring pressure has a very definite effect, wear apparently increasing in the proportion as ring pressure. You will see, therefore, that we have no desire to fit these rings as standard with the existing design of engine, but if the car is hard driven we know that wear is less than a car used gently, therefore, we are hoping that fitted in the right car wear should not be excessive. We do not wish you to increase the oil pressure in any way and recommend that the relief valve is left standard in every way, we have recently seized the engine gears on a chassis in which we attempted to increase the main oil pressure, generally speaking we now believe that if pressure is low it is due to slack bearings, which although the pressure is lower than standard, are passing considerably more oil. The rings of these pistons should have a gap of .009-.013 inches and should you remove the rings, we wish to point out that the compression rings are taper faced and must only be fitted one way, these rings are stamped and no mistake can be made if care is taken, the scraper rings of course can be fitted either way. Rm{William Robotham - Chief Engineer}/Mths.{Reg Matthews} | ||