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).
Use of long toed cams and steel push rods to manage tappet clearance and noise.
| Identifier | ExFiles\Box 179\1\ img095 | |
| Date | 19th November 1931 | |
| HS.{Lord Ernest Hives - Chair} FROM R.{Sir Henry Royce} C. to SG.{Arthur F. Sidgreaves - MD} WOR.{Arthur Wormald - General Works Manager} BY.{R.W. Bailey - Chief Engineer} [crossed out] TAPPET CLEARANCE. R4/M16.11.31. Sent off 19.11.31. X 7090. X 5090. For very many years we have tried to introduce a long toed cam as a means of getting silence for any variation in tappet clearance. The Expl. Dept. have failed to get any advantage from this. In discussing the matter with E.{Mr Elliott - Chief Engineer} in reference to J.{Mr Johnson W.M.} 3. I can see that this form of cam ought not to make noisy tappets if it is arranged that the clearance decreases when cold, which would be the case if the push rods had a small co-efficient of expansion such as would be used by steel rods or tubes. The cyl. block and crankchamber would always be running away and increasing the tappet rod clearance, which could be arranged to be correct when the whole thing is warmed up. At all other times the clearance would decrease which would not make a noisy engine, but would make a cold engine, and appear to have extra long duration cams. The timing cold and during warming up would not be important, and the clearance hot would be ample, and might be thought excessive, but ought not to prove noisy. These required conditions are obtainable with steel push rods, which would simply lose clearance as the engine cooled down. R.{Sir Henry Royce} | ||