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).
Technical discussion on the issue of piston ring gumming due to increased clearances in reground cylinders.
| Identifier | ExFiles\Box 66\1\ scan0134 | |
| Date | 9th March 1927 | |
| R.{Sir Henry Royce} from E.{Mr Elliott - Chief Engineer} to BJ. RG.{Mr Rowledge} Hs.{Lord Ernest Hives - Chair} BY.{R.W. Bailey - Chief Engineer} 18040 E1/M9.3.27. X.3996 X.2103 X.8040 X.2603 GUMMING UP OF PISTON RINGS. It is noticed in report Hs{Lord Ernest Hives - Chair}2/LG7.3.27., that reground aero cyls. up to .015" large may be used in conjunction with std. pistons because of the difficulty with spares, and that this practically doubles the piston clearance. This latter statement appears to us to only apply when the engine is cold. Assuming that the cyl. wall reaches a temp: of 100°C. and the piston body 150°C. then the standard hot clearance is about .007" if the cold clearance is .016". The hot clearance with a regound cyl. would be .007 plus .015 = .022, or three times std. hot clearance. This rather suggests that it would be worth while measuring the cyl bores and pistons of the Condor allotted for the last type test, and also running cyls. on test, with widely different piston clearances, in an endeavour to produce gumming up at will. Car engines are said to suffer from gumming up after long mileages which no doubt would be when the cyl. bores became worn. It might appear that with .022" hot clearance pistons, especially the short ones used on aero engines, would have difficulty in keeping themselves cool. There are also one or two reason why they should be less gas-tight under these conditions. E.{Mr Elliott - Chief Engineer} | ||