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).
Diagnosis and potential cures for piston knock troubles.
| Identifier | ExFiles\Box 148\3\ scan0048 | |
| Date | 7th February 1928 | |
| U16.R.2.7.28 XC490 February 7th, 1928. TO Mr. Caswell Mr. Nadin(England) Mr. Ainsworth cc - Mr. Beaver Mr. Burton FROM Mr. Olley RE PISTON An accurate diagnosis of our piston knock troubles appears essential as the first step towards curing them. Cold knocking is the general classification but this does not occur at the few moments of starting only but persists until the engine is thoroughly warm. On 364-FM with the extra oil connected with carburation control, it is easy to prove that this arrangement is effective in preventing cold knocks at starting, because by starting with the carburation lever 2 notches to the left of full strong (i.e. with oil valve closed) the knocking is very marked, whereas with carburation lever full over there is no knocking. But this arrangement does not solve the trouble entirely as piston "taps" show up as soon as the carburation lever is brought central (say 3 mins. after starting) and persist for perhaps 15 minutes until the engine gets thoroughly warm. 364-FM may be unfortunate in this respect but reports from depots indicate that similar trouble is widespread and there seems no certain knowledge as to cause and therefore no certain way of curing it. Furthermore we do not produce this effect on test as we operate all the year round from room temperature upwards, whereas a large number of our cars are never in a warm garage during the winter and have to operate down to zero fahrenheit. 364-FM would never have passed test if it had been operated under cold-garage conditions such as I use. Now we have to find out:- (1) Is the trouble due to dry bores and if so can it be cured by using 4 plain rings and one L section? (2) Is the trouble due to expansion of the skirt and if so can it be altered by Waltham Avenue's method of filing the sides of the skirt to cancel the full circular fit at the bottom? (Continued) | ||