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).
Investigation into the source of Bentley tappet noise and the ineffectiveness of insulating the rocker cover to reduce it.
| Identifier | ExFiles\Box 102\5\ scan0152 | |
| Date | 11th December 1933 | |
| To Sg.{Arthur F. Sidgreaves - MD} From Hs{Lord Ernest Hives - Chair}/FJH.{Fred J. Hardy - Chief Dev. Engineer} c. Hsr. E.{Mr Elliott - Chief Engineer} c. By.{R.W. Bailey - Chief Engineer} Rn.{Mr Robinson} c. Bv. Hs{Lord Ernest Hives - Chair}/FJH.{Fred J. Hardy - Chief Dev. Engineer}11/KT.11.12.33. BENTLEY TAPPET NOISE. The first part of this investigation consisted of attempts to reduce the tappet noise on the Bentley (Unit E.7) by insulating the rocker cover from the cylinder head and from the rocker pedestals by means of felt washers. The following conditions were tried :- (1) Standard rocker cover arrangement. (2) Extra felt packing under rocker cover. (3) Standard arrangement of rocker cover holding down screws with different degrees of tightness. (4) Holding down screws removed completely. (5) Felt washers placed between holding down screws and cover. No combination of the above conditions was found to make any difference to the tappet noise. It was noticed during these tests that the tappet noise was much louder at the sides of the cylinder head than it was above the rocker cover. This suggested that the cylinder head was playing a greater part than the rocker cover in transmitting the noise to the outside, and that it was the seating of the valve that was causing the noise and not the closing of the tappet clearance between the valve stem and rocker. To determine whether this was so, all tappets except one were set with zero clearance. The one tappet was given .010" clearance. The engine was then run slowly and the noise of the one tappet synchronised with the position of the valve. This was carried out on two inlet valves and two exhaust valves, and in all cases it was the closing of the valve that caused 80% of the noise. As a further confirmation all tappets were set with .004" clearance and with the engine running at about 1000 r.p.m. oil was put into the carburetter intakes. This caused a slight but distinct reduction of the noise. This is attributed to the fact that the oil was getting on to the valve seats and cushioning the impact of the closing of the valve. | ||