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).
Issues and solutions related to engine push-rod mechanisms, valve bounce, and tappet lubrication.
| Identifier | ExFiles\Box 17\6\ Scan194 | |
| Date | 20th February 1934 guessed | |
| -2- As soon as separation in the push-rod mechanism takes place, however slight, the eccentric and plunger follow up and take up this clearance - the oil under the plunger has not time to leak out when valve closes. This is repeated during the next revolution, so that the effect is cumulative, i.e., if the valve bounce were only a matter of a few thousandths of an inch, the successive effects would add until the eccentric had reached the limit of its upward movement, thus holding the valve off its seat by an amount of approximately .025". (We are at present having a piece of apparatus constructed for attachment to the Phantom ignition tower, by which we hope to be able to detect and record small amounts of valve bounce). Finally, some very high rating springs with a high loading (approx. same initial loading as springs which were successful up to 3350 r.p.m.) were fitted and these enabled us to run up to 3500 r.p.m. without trouble. The plunger clearance was also increased to .0015" as this did not impair the operation of these tappets and allowed eccentrics which were holding valves off their seats to return to the normal position much more quickly at idling speeds; also it is desirable to use the maximum successful clearance from production considerations. Another difficulty with these tappets was to ensure a continual supply of oil to each plunger casing - the inclined drilling of the casings was not sufficiently accurate to make the supply of oil to each equal, while the variation in plunger positions had the same effect. This set of tappets was fitted to a car and run, but although no failures in operation were experienced, there was intermittent noise from various tappets, due to general sticking of the eccentrics. This, we think, is caused by distortion of the shaft and inadequacy of the eccentric bearing. | ||