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).
Confidential memo detailing solutions for crankshaft vibration in the 25HP engine at high speed.
| Identifier | WestWitteringFiles\V\October1930-February1931\ Scan005 | |
| Date | 1st October 1930 | |
| HS.{Lord Ernest Hives - Chair} FROM R.{Sir Henry Royce} [Text struck through] Copy to SG{Arthur F. Sidgreaves - MD} Copy to WOR.{Arthur Wormald - General Works Manager} Copy to BY.{R.W. Bailey - Chief Engineer} Copy to E.{Mr Elliott - Chief Engineer} Copy to C. [End of struck-through text] CONFIDENTIAL. 25HP. CRANKSHAFT VIBRATION IN APPROACHING 70MPH. [Stamped across text: ORIGINAL] Naturally we realise that this is a very high engine speed which has come about through our low top gear. we cannot at the moment do very much to alter the design so that this vibration shall not take place until the engine has considerably increased in speed, and the only thing we can do, as far as I can see, is as follows:- (1) Stiffen the crankshaft with the wider crank webs which we have adopted since this engine was designed, and use the 2" pin and the 2-1/8th journal diameter. This should put the speed up something and render the vibration less vigorous. (2) The 2nd. thing we can do is I fear much less effective. It consists of reducing the overhang weight of the flywheel, and the flywheel's moment of inertia generally. Had it been the bending of the crankshaft this reduction in flywheel weight would have been effective in altering the periodicity of the phenomenon. If however the cause is due to getting near the master period of the crankshaft which I think may prove to be so this alteration of the flywheel will only have a very small effect on the speed at which it occurs, and its vigour - (i.e. by shifting the node.) We believe however this is all we can do at the moment. We are busy making you a new cast iron head for this engine which is capable of (1) using 2 carburetters, (2) improved distribution, and (3) double ignition, which will probably be found to be favoured greatly by buyers. A drawing of this head will be ready in probably 2 days from now. We have just decided that with the 2" pins and new cyl. block we can lengthen the con. rods: this we have included and are instructing. R.{Sir Henry Royce} | ||