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).
Analysis of engine big end failure and cylinder lubrication issues.
| Identifier | ExFiles\Box 132\4\ scan0261 | |
| Date | 3rd February 1944 guessed | |
| -2- probable that insufficient lubrication has been a problem on this engine, because these clearances have never been right since the unit was built. M.40. Total Mileage 6506. This engine has a big end failure at 5329 miles. Since we do not know the initial clearances when the unit was built, it is probable that insufficient oil up the bores is a contributing factor also on this engine. Note: B.60. No.1 (Bentley Lorry) has completed 58023 miles with Vandervell big ends, and maximum cylinder wear is .008". Cylinder Lubrication. The following questions arise :- (1) Is less oil thrown up a smaller bore? (2) What is the value of an oil jet in the rod? (3) How is the problem influenced by bearing clearances? Taking these in order (1) It is reasonable to expect, that as the size of bore is decreased, oil will not be thrown so far up the cylinder, for an unaltered throw of 4.50" stroke. (2) Experience shows that in the past, an oil jet in the con-rod has had no effect whatever on rate of wear. This is true for comparative results on our cars during this war, as it was on Series "C" and "D" 3½ litre Bentley. (3) This is an important point, and it is as well to consider the various big end clearances as required with different materials. White Metal - .00275 A.C. 9. - .0035 L/B - .0035/.004 Vandervell - .0005/.002 It is at once obvious, that if one works to the bottom Vandervell limit, there is practically no clearance at all, and therefore very little oil will be thrown up the bore. There are two other factors which have to be included, one of which has never really been understood. (a) Type of piston. (b) Length of cylinder skirt. --continued-- | ||