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).
Premature valve bounce using Halford Tappets on a Bentley engine, comparing single and double valve springs.
| Identifier | ExFiles\Box 88\4\ scan0077 | |
| Date | 3rd July 1934 | |
| X254 To E.{Mr Elliott - Chief Engineer} c. to Wor.{Arthur Wormald - General Works Manager} c. to By.{R.W. Bailey - Chief Engineer} Hs{Lord Ernest Hives - Chair}/Smth.3/KW.3.7.34. Halford Tappets on Bentley Engine. As on Phantom, premature valve bounce occurs on Bentley when fitted with Halford Automatic Tappets. The following results have been noted on a test Unit provided with standard exhaust valves and large inlet valves (EX.12089). With Standard Single Valve Springs - Designed seating load and rating 56 lbs. & 115 lbs/in. Nos. 3, 5 & 6 exhaust valves bounce at 4200 r.p.m. All valves (inlet & exhaust) bounce at 4500 r.p.m. With Double Valve Springs (EB.507/B) - Designed seating load and rating 43 lbs. & 150 lbs/in. No. 3 Exhaust Valve bounces at 4000 r.p.m. Nos. 3, 4, 5 & 6 exhaust valves bounce at 4200 r.p.m. All valves (inlet & exhaust) bounce at 4500 r.p.m. The tappet spring is sufficient to control the tappet at the theoretical bouncing speed. The total equivalent weight actuated by the exhaust valve spring is .496 lbs. with the standard tappets, and .636 lbs. with the Halford tappets. The actual bouncing speed with the standard gear is about 4800 r.p.m. The Halford tappets would be expected to reduce the speed to - 4800 } .496 / .636 = 4250 r.p.m. which is in good agreement with the actual figure. | ||