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).
Analysis of valve and cam noise, comparing materials and measuring cam contours to determine quiet operating velocities.
| Identifier | ExFiles\Box 102\5\ scan0153 | |
| Date | 11th December 1935 | |
| -2- Hs{Lord Ernest Hives - Chair}/PJH.11/RT.11.12.35. The noise due to the impact of the valve on its seat should be proportional to the velocity of impact, the mass of the valve, cap, and cotters, and the rigidity of the seat in the cylinder head. The Bentley has a cast iron head with solid seats. This arrangement gives a very rigid seat. It is possible that an aluminium head with bronze seat inserts is less rigid and less liable to valve seating noise. As the closing of the valve is noisy and the opening relatively quiet it is evident that the closing and opening toes of the cams could be lengthened and shortened respectively. An attempt was therefore made to determine the maximum closing and opening velocities for quiet operation. The maximum clearance for quiet closing and opening of the inlet and exhaust valves Nos 1 and 2 cylinders was determined. The results are shown on sheet 1. The opening and closing toes of the four cams were then measured and are shown on Sheets 2 - 5. It will be noticed that the contour of the toes is of very irregular shape. This would seem to be due to errors of measurement but several of the cams show similar irregularities and this suggests that the irregularities are present on the master cam. For this reason the contour curve shown is drawn through all the measured points and is not an average smooth curve. The designed shape of the cam is shown dotted. The tappet clearances given on sheet 1. were measured with the engine on T.D.C. of the firing stroke. As the base circles of the cams varied appreciably from the round it was necessary to measure their contours in order to locate the point of valve opening and closing on the cam toe contours. The base circle contours are shown on sheet 6. The max. permissible closing and opening velocities are shown on sheet 1. The results are not very consistent, possibly due to undetected irregularities of cam form, but if a rough average is taken it may be said that for quiet closing the velocity should not exceed 0.00040" per degree (crankshaft) and for quiet opening 0.00055" per degree. | ||