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).
Variation in tappet clearance for overhead camshaft engines due to temperature effects.
| Identifier | ExFiles\Box 133\2\ scan0174 | |
| Date | 4th July 1935 | |
| Hs{Lord Ernest Hives - Chair}/Smth.10/KW.4.7.35. Overhead Camshaft Engine. Variation in Tappet Clearance. We have been estimating the variation in tappet clearance we should have to provide for on an overhead camshaft engine due to temperature effects whilst running. On a Bentley type and size of head, using a KE.965 exhaust valve, the maximum change occurs just after starting up, when the head is cold and the valve is hot. At this stage the clearance will have decreased by .005" whether the head is of cast-iron or aluminium. When the engine is thoroughly hot, and running under load, the tappet clearance will be .004" less than the cold clearance with a cast-iron head and .002" less with an aluminium head. The maximum variation in tappet clearance on an existing 20/25 HP. occurs during warming up when the water is hot, and the oil, which controls the push rod temperature, is cold. We find that at this period the tappet clearance has increased about .005" from the cold setting. This figure is the same as on the overhead camshaft engine, but in the opposite direction. Thus, by using a 20/25 closing toe on the cam form, we ought to be able to obtain tappets as quiet as on a 20/25 engine by applying an overhead camshaft to either a cast-iron or an aluminium head. Hs{Lord Ernest Hives - Chair}/F.LL.Smith. | ||