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).
Camwheel failure due to crankshaft oscillation and a discussion on valve gear spring design to prevent bounce.
| Identifier | ExFiles\Box 134\2\ scan0197 | |
| Date | 1st February 1939 | |
| -10- which speed the oscillation is .45 degree. After a further 34 hrs. the new camwheel failed in the same manner as the first, i.e. stripping the teeth. We cannot forecast how much we shall be able to reduce the crankshaft oscillations, however, the fact that camwheels fail when an oscillation of .5 degree is transmitted to them shows that to be safe, the damper should be capable of cutting down the oscillations to a negligible amount. As shown on our previous engines with the spring drive type of damper no crankshaft oscillations get through the spring drive at top speeds, despite the fact that the crank may oscillate to the extent of 1 - 2 degrees. This appears to be the saviour of the fibre camwheels, now standard practice. VALVE GEAR. With standard raith single valve springs EB.3256 the inlet valves bounce at 4000 r.p.m. and having no stronger single springs available, Ph.III double springs were used which raised the bounce speed to 4500 r.p.m. During 50 hrs. endurance one outer spring failed, which we consider is due to bad surging, these springs having no close coils at the base which has proved a successful anti-surge device. There is enough room to try an alternative single spring which will give the required non-bounce seat loading, approx. 50 lbs. and yet be subject to no higher stress than the EB.3256 spring which has proved satisfactory on the Bentley V.{VIENNA} The spring in question is to EB.4373 and is similar to EB.3256 with the exception that it contains another half coil of wire. De/Jnr.{Charles L. Jenner} has designed double springs for trial on Bentley V to PD.354 these including the close pitch anti-surge base coils. We consider that the new head should be equipped with these springs. The above remarks only apply to the inlet valves as we have had no failure or bounce on the exhaust valves. One important thing we should cater for is to prevent the push rod coming out of mesh in the event of valve sticking or spring failure. Carried out only by extension of the top cup makes the rod an unsightly and expensive proposition. If possible, this should be carried out by combination of reduced diameter push rod tubes and increased diameter of ball and cup at the top of the rod. | ||