Investigation report on the timing gears of the Wraith III, focusing on camwheel wear and rattle.
| Identifier | ExFiles\Box 7\8\ X 607 Camshaft-page31 | |
| Date | 12th April 1938 | |
| 12th April, 1938. WRAITH III TIMING GEARS. This report is further to our original memo Rm {William Robotham - Chief Engineer} /Swdl. {Len H. Swindell} 4/JH.19.1.38. and written in view of the wear of the Fabroil camwheel and rattle which has developed on 26.G.VI. Continuing with our original investigation on the effect of deleting the cam balancer, this was tried on half- a-dozen Wraith III units without bringing up any rattle whatever. In one extreme case a backlash of .015 was machined in the gears without any resultant rattle, therefore, we are positive that if the camwheel had worn evenly on 26.G.VI there would have been no rattle and that it is the uneven backlash between the gear teeth that is the cause of this rattle. This appears to be between the camwheel and dynamo pinion as a load applied on the dynamo drive cures the trouble. If the out-of-balance of the cam when running with- out the cam balancer were responsible, then the rattle would be there irrespective of whether the backlash were even or uneven and we know that it only exists with the latter condition. Further confirmation of the fact that the deletion of the balancer is not responsible, is that when the camshaft is turned over by hand the friction exe(Aero Engine)rted by the new type of bottom tappets is in excess of the out-of-balance (due to valve spring loading), therefore, there can be no uneven drive transmitted from the camwheel. In the case of the 25/30 and Bentley II, there is no friction by reason of the roller tappets and the out of balance due to the valve springs takes charge of the camshaft rotation at the low speeds, thus producing a pulsation in its drive, hence the institution of the cam balancer and its counter effect to cure the low speed rattles. In view of our experience, therefore, we do not consider that running 26.G.VI. without the cam balancer has had anything to do with the large uneven wear or rattle. We are investigating on the following lines - (a) That the uneven wear is the result of crankshaft oscillations at the high speeds which from diagrams, is bad, transmitting its effect through the gears, or (b) Inertia torque of the valve gear to which the effect of with or without the balancer is negligible. | ||
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).