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 letter discussing modifications to the Goshawk 11 engine's exhaust cam timing due to experimental results showing it as too short.
| Identifier | ExFiles\Box 43\1\ Scan003 | |
| Date | 13th July 1923 | |
| X3942 To Hs.{Lord Ernest Hives - Chair} from R.{Sir Henry Royce} c. to CJ. BJ. Wor.{Arthur Wormald - General Works Manager} c. to PN.{Mr Northey} BY.{R.W. Bailey - Chief Engineer} EP.{G. Eric Platford - Chief Quality Engineer} RE. GOSHAWK 11. TIMING. X.3942 X.1770. Our letter of the 12th. inst., states that the exhaust cam is too short as given on your recent diagram, whereas if made to instructions shewn on our LeC. 1044 & 1050., it is of ample length, and there is some definite mystery as to why the Goshawk.11. exhaust cam shews in the experiments to be too short. The only modification we can see is necessary to make from the instructions as originally sent you is that the angle between the cam shall be reduced from 118° to 108°. We suggest however so as not to go too far that you should test 110°. Let us be sure that the exhaust cam gives the lift as shewn in the curve on LeC.1050., by seeing that the rapid acceleration is in the correct position. It begins at 13 divisions, and ceases at No.69 division on the diagram. This diagram says that the duration of the exhaust valve lift with .010" clearance should be 60 divisions, that is, 120° on the camshaft and 240° on the crankshaft. Our experimental record shews that the exhaust valve you have got on the engine has only a duration of lift of 56 divisions, that is 224° on the crankshaft, which is 16° short of the original instructions. Similarly it is found that the duration of lift of the inlet valve instead of being 56 divisions, is only about 54, that is, 8° less on the crankshaft. We should expect the modification to the timing shewn on your experiments, to result in more power at low speeds, less at high speed, and perhaps a rather coarser engine, which will demand a reduction in compression. If so be sure we are doing right by - (1) opening the exhaust later and (2) closing the inlet earlier (this latter I doubt most). I quite believe the overlap will be found good. R.{Sir Henry Royce} | ||