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).
Piston carbon build-up and knocking issues on vehicle 49-GB.
| Identifier | ExFiles\Box 35\2\ scan 190 | |
| Date | 15th January 1920 | |
| Contd. -2- Hs{Lord Ernest Hives - Chair}/1/LG15.1.20. on 49-GB, we left the normal clearance on the top band. After seeing the pistons on 49-GB, however, we think this should certainly be cleared away, leaving only the narrow fitting band. If the top of the band is cleared away, we think that it is still effective as regards protecting the rings from the hot gases. We are sending to Mr. Royce a piston off 49-GB which plainly shews the marks formed by carbon on the top band; The cause of it appears to be due to the fact that at every explosion a certain amount of oil is carbonised; the rings scrap this off of the cylinder bore over which they travel but on the top of the cylinder which the rings do not touch, this accumulates. For light and moderate running as the piston does not expand full, this does not cause any noticeable effect. With full throttle running when the piston expands itself to maximum, it has to force its way through the carbon. The knock appears to be caused by the piston becoming very tight and the slack in the gudgeon pin and bearing being taken up. It is an exactly similar noise as we get when a piston seizes. Hs.{Lord Ernest Hives - Chair} | ||