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).
Big end failures in the Merlin engine, detailing failure rates and proposed modifications to the lubrication system.
| Identifier | ExFiles\Box 144\4\ scan0110 | |
| Date | 23th July 1940 | |
| Handwritten notes: -11824 see also 2026 "Hs{Lord Ernest Hives - Chair}" from "Rm{William Robotham - Chief Engineer}" c: "E", c:"By", c: "Lov{Mr Lovesey}", c: "Wd{Mr Wood/Mr Whitehead}". COPY Big End Failures - Merlin. Hancock's report of service troubles for March, April and May 1940 indicates that, though main bearings were found to be in an unsatisfactory condition after the engine had been stripped, these were not the main causes of engine failures. Big end troubles, on the other hand, accounted for 7½% of the engines failing completely, and 4½% of the engines having partial failures, the figure of 12% must be considered unsatisfactory. A larger capacity oil pump and increased feed from the main bearing has already been introduced by "By", and is evidently a progress in the right direction. We suggest, however that a further step might be taken in view of our car experience, and a second hole introduced into the pin. We found that this improvement in the oil distribution was necessary for high speed light throttle running. The oil passage was not increased in diameter; two small holes taking the place of one large hole. This modification entirely eliminated failures which could be produced in 5 minutes or less light throttle running, maximum revs. We attach a copy of Print Rm.{William Robotham - Chief Engineer}447 which shows the logical development of the lubrication system on the Bentley and subsequently on the Phantom III, to accommodate higher engine speeds, and the use of big end bearings other than that of Babbitt to produce high resistance to fatigue. The major steps taken to eliminate failures were as follows: 1) It was found that any non-continuous grooves in a bearing fitted into a crankshaft would not allow an adequate supply of oil to pass at high speeds, due presumably to the column of oil being reluctant to stop and start each revolution. 2) It was ascertained that, in order to get an adequate supply of oil to the bearings, it was necessary to have a continuous oil feed to every crankshaft main bearing. 3) It was found necessary for each big end to be supplied from two main bearings. 4) The modification mentioned previously in this memo, i.e. two holes in the pin, was found to be essential for light throttle high speed running. We notice there are two holes in the pin on the Vulture crankshaft. (continued) Faint stamp near item 3: 26CCUOU Faint stamp near item 4: no' CU' no' lpa' osa' Faint stamp bottom left: T/ROLL (19..) LTD DERBY D... | ||