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).
Technical discussion on engine smoothness and vibration, comparing the 20 HP engine with competitor models and considering improvements like counter-weights.
| Identifier | ExFiles\Box 25\3\ Scan380 | |
| Date | 9th January 1929 guessed | |
| contd :- -4- I think this is an uneconomic application of weight, which would be of more advantage in the crankshaft. Also I think [s]moreover[/s] that too much steadying of the crankshaft by means of the bearings must entail increasing the loads on them, since it gives them more to do. In fact we can say that the loads on the bearings at very high speeds depend mainly on their stiffness and capacity to resist vibration of the crankshaft. From the above you will see why I think that although counter-weights on the SS.{S. Smith} should shew an improvement it is by no means as far as we might go. I do not think it worth while to fit them to the 20 HP. Since it is proposed to render 3500 r.p.m. attainable on 3rd. gear in the 20 HP. car, I recommend that we do experiments on this, on a more wholesale scale. This engine should be smooth at much greater speeds than the Phantom, on a basis of size and piston speeds. Actually it is not much smoother, and I think therefore that it is not such a good engine for smoothness as the Phantom. The Stutz and Alfa Romeo cars (4880 and 1500 c.c.) we have tried with solid engine feet, are both smoother at high revs than our 20 HP. with rubber engine mounting. The Chrysler (4080 c.c.) is far smoother, and does 3400 r.p.m. in 2nd. gear and 3000 r.p.m. at 60 m.p.h. in top. The engine roars slightly but there is no vibration. We think this roaring may be the result of a cast iron crankcase. I think it must be admitted that there is something fundamentally different to make our 20 HP. so rough compared with a semi-racing engine like the contd :- | ||