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).
Engine vibration, balance weights, and potential improvements by using thicker webs and larger pins.
| Identifier | ExFiles\Box 13\7\ 07-page085 | |
| Date | 6th February 1931 guessed | |
| (2) We have from time to time increased the pins and not been altogether satisfied that they have made much improvement - i.e. the added weight has done as much harm as the increased stiffness has done good. Exactly if this is so I do not know but it may be accounted for by the flexibility being in the webs. I suggest therefore that we try somewhat thicker web and trust to either nitro-hardening or the improved stiffness compensating for the loss of surface, which it can easily do if the metal(liner) will stand the load, as appears possible with B.L. Test therefore thicker webs and larger pins. The foregoing is for putting up the speed of vibration and is hoped may take it out of the range of useful speeds, and this can be helped by gearing the cars 9% higher by the use of one or more tooth in the back axle bevel - i.e. the 3 types of springing should have three ratios of backaxle. If however we find it difficult to get beyond the speed range we should have induced its intensity by what we have done, and we can still more do so by the use of balance weights. Now from Mr. Grylls estimates, if I read them rightly, there would be very little improvement from a stiffer crankcase, but there would be much from a heavier one, but as this would overload the bearings as well as make a heavy engine one can see that this extra weight is much better put into balance weights, and also, more important still is that the balance weights are directly reducing the disturbing forces so that if we could only counter-balance 30 to 50% we should reduce the deflections and bearing loads from 100 to less than 70 and 50, and as we have slightly increased the mass to be moved (quoting Mr. Gryll's calculations) smoothness and life of our engine goes up. These are the main reasons for even the smallest balance weights. Supposing therefore if we could take 1/10 of a lb. from the pin side and put it on the counterweight it would count 2/10 without altering the master period. Now that we can so exactly tell the master period because we can keep it clear of this particular vibration we can fit balance weights that will on any particular crankshaft just keep the master period safely below the maximum possible speed, which seems to be fairly well defined. For instance our car here very rarely indeed touches 80, and never much beyond. It might go something more if higher geared, or on a long down hill, or following wing, but I think Mr. Hancock would say that this is very rarely met, so we can have some balance weights on all engines. | ||