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).
Notes on crankshaft specifications, balancing, crank dampers, and gearbox design.
| Identifier | ExFiles\Box 173\1\ img425 | |
| Date | 19th February 1934 | |
| -3- CRANKSHAFT 12 cyl. Pins 2 1/4 dia. 2 1/4 long. Journals 2 3/4 dia. Central mains 1 3/4 long, 60% balanced. Shaft length flywheel to termination of front bearing 33-11/16". 4 bearing shaft 60% total balance. BALANCING Shaft, flywheel etc. all held to 2/10 inch oz out of balance (dynamic). Selective assembly of flywheel on crankshaft flange. Con. rods, no panel machining held to 1/32 oz. for weight. Packards say that they were forced to these close limits on out of balance, and that they can definitely detect anything above 2 ins. oz. out of balance on the road. I do not think that we can parallel their results, but might with advantage do some tests on a number of cars whereby we find an average of how much out of balance we can detect. LIGHT & CRANK Nine bearing 2-3/16 pins 2-5/8 journals. No troubles with crankshaft periods. I enclose a print of the crankshaft damper that they employ on all cars. You will see that it is a combination of a rubber spring with friction damping, and as such I should expect it to be very effective. They say it deals with a wide range of frequencies better than the Lanchester, stays put indefinitely, and costs 3 % per car less. They prefer it to the Chrysler type which they say gave them some difficulty. If you want one of these dampers you can buy one from - Leonard Williams, Great West Road, LONDON. GEARBOX On the 12 cyl. in particular remarkably good. They use 10 pitch teeth, 45º helix angle, and use lapping only, no grinding. They modified the S.K.F. races slightly to take the increased thrust of the high helix angle, that is all. They have been using this box for two years with complete satisfaction. They get better results with 10 pitch than with finer gears, due they consider to the fact that they found the finer teeth were deflecting as much as .003 under load. | ||