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).
Investigation into offsetting tappets for right and left-handed engines and its effects on the valve gear.
| Identifier | WestWitteringFiles\T\January1929-February1929\ Scan101 | |
| Date | 5th February 1929 guessed | |
| FROM E.{Mr Elliott - Chief Engineer} Copy to BJ. " HS.{Lord Ernest Hives - Chair} " BY.{R.W. Bailey - Chief Engineer} SECRET. SS.{S. Smith} VALVE GEAR & LEFT HANDED ENGINE. ORIGINAL E1/M1.2.29. X7060 X7090 X7772 Regarding further the question of right and left handed engines BY.{R.W. Bailey - Chief Engineer} has made a suggestion that the tappet could be offset instead of the camshaft. The camshaft would then lie on the centreline of the push rod mechanism and would render the timing gears interchangeable for R.{Sir Henry Royce} and L.H. engines. We thought this suggestion was worth some investigation and attach blueprints LeC. 2661/2. dealing with this matter. The first named drawing shews the inlet cam form we are using, while the second shews in large scale the path of the point of contact between this cam and its follower. The full lines shew the tappet with the curved end offset, and the dotted lines shew where the present tappet comes relative to the camshaft. A number of interesting points emerge from this investigation: The period of heavy pressure is spread over the whole of the contact face of the tappet and over a large part of the working face of the cam. The .100" desaxe we work to allows for a co-efficient of friction between cam and tappet of .07" for symmetrical loading of tappet guide which is probably very near the result in practice for average lubrication. The lop-sided tappet is no worse than our present tappet in respect to the actual rubbing surface being near one edge; but against this it is nearer the leading edge. With the lop-sided tappet it might be said to introduce bending into the tappet stem due to the load being out of centre but in practice the frictional effect appears to move the virtual roller centre towards the tappet centre line. The present timing gears would require some alteration to move the camshaft. The biggest objection that we can see is that some definite means must be provided to ensure that the tappets cannot be assembled the wrong way round in their guides. There are a number of ways of doing this but we have shewn a taper pin sticking out on one side, to clear which a groove is provided in one side of the tappet guide. The hole for this pin has to be reamed before hardening the tappet. While on this question of tappet mechanism it might be mentioned that we looked into the question of running the camshaft and tappets completely immersed in a trough of oil as you requested, and find it means raising the camshaft about .750". E.{Mr Elliott - Chief Engineer} | ||