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).
Outstanding troubles with the Wraith engine unit, specifically engine roughness and valve gear noise.
| Identifier | ExFiles\Box 108\1\ scan0069 | |
| Date | 9th August 1937 | |
| SECRET. (D.O.a) By.{R.W. Bailey - Chief Engineer} from Rm.{William Robotham - Chief Engineer} c. Hs.{Lord Ernest Hives - Chair} c. RHC.{R. H. Coverley - Production Engineer} Rm{William Robotham - Chief Engineer}5/R.9.8.37. WRAITH ENGINE UNIT. The outstanding troubles on the Wraith engine unit now running in France are:- (1) Engine roughness at high and low speed. (2) Valve gear noise. (3) Vapour lock on the mechanically-operated petrol pump. (1) The low speed roughness has been cured by modifying the engine mounting. The high speed roughness has been reduced by reverting to the integral construction cylinder block. Confirmation reqd. The large diameter crankshaft is very slightly better for engine vibrations, but if it is really going to cost 25/- more as a forging, as we are led to believe from the figures received from the Cost Office, then we shall seriously have to consider reverting to the present standard 25/30 crankshaft. We should like to have RHC{R. H. Coverley - Production Engineer}'s considered opinion on this matter when he has time to go into it. (2) The valve gear noise has been largely eliminated by increasing the length of toe on the camshaft, but in order to improve the timing gear position, we are proposing to try reducing the valve gear lift slightly. It seems probable that this will be successful in enabling us to use weaker valve springs, and so reducing the chance of timing gear rattle. It will mean that the rockers cannot be finalised until we have concluded the experiments, which may take 3/4 weeks. In our opinion, the timing gears are still by far the most unsatisfactory feature of the Wraith engine. Going from five to three gears has not made the improvement which was originally anticipated, and we consider that intensive work by production is very necessary. Our only move at present experimentally is to try a greater helix angle. Apart from rockers, we propose to release the engine complete in a fortnight's time, when we shall recommend that the Works take steps forthwith to get some information on this timing problem. | ||