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).
Valve gear design, clearances, and proposed modifications for Phantom & EAC.10 engines.
| Identifier | ExFiles\Box 17\6\ Scan036 | |
| Date | 7th May 1928 | |
| HS.{Lord Ernest Hives - Chair} from R.{Sir Henry Royce} BY.{R.W. Bailey - Chief Engineer} c. to BJ. Wor.{Arthur Wormald - General Works Manager} 77060 R4/M7.5.28. PHANTOM & EAC.10 VALVE GEAR. X. 7060 X. 615 We believe that there is some other reason than the actual effect of the cam that causes you to use fine clearances when setting the valve tappets on chassis engines. The cams are designed for a hot clearance of 5 thous., and hence a cold clearance of 8 to 10 thous., the latter applying only to the exhaust. We therefore do not know why you are setting your clearances so fine. We have been considering the cam forms for EAC.10 and the following particulars include I believe all the recent moves we have learnt in connection with car and aero engines. In the first place we do not propose to increase the valve lift of the larger inlet valve but rather to fatten the valve lift curve. The lift remains therefore at .423 or thereabouts, and the present SS.{S. Smith} double valve springs will be used. We are counting on the springs increasing 75% between the up and down positions. We are counting on 5% difference in the two halves of the cam due to rubbing friction or gas friction. We are counting on 8% difference of weight between exhaust and inlet valves. Regarding the cam foot there is very little wrong with this, but we propose to simplify it by increasing the period of the first acceleration, and then proceeding with no acceleration at all to the same point of lift where the foot finishes now. We are counting on a running clearance when hot of .005, and we are ignoring the slight opening at .008 in the actual running of the engine. The cold clearance we are estimating would not exceed .010". The push rods and expansion of the blocks is assumed to keep the clearance normal. The only difference would be in the exhaust valve taking up, so that the exhaust valves should be set with more clearance. Should we be correct in saying the inlets should be .005 and the exhausts .008" cold? contd :- | ||