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).
Results of numbered engine vibration and performance tests under various conditions.
| Identifier | ExFiles\Box 3\1\ 01-page083 | |
| Date | 27th May 1928 guessed | |
| -2- 2 As above throttle closed. The period at 500 to 640 revs as now practically disappeared, it has left a slight period from 600 to 620. over 800 revs, the vibrations are much worse, they can be felt all the time, immediately the throttle is open they disappear, the period at 900 to 940 is bad, between 1100 to 1200 is bad, after 1400 revs. The difference of open and closed throttle is not so marked. 3 As above with brass plugs removed from cylinders. Under this condition the vibrations are less than No. 2 test but not as good as No. 1. there are good patches but the periods are very distinct, 600 to 620 revs, 900 to 940 & 1100 to 1200. 4 Connecting rods & pistons removed run-ning crankshaft only. There is no sign of a period & nothing could be felt until run 1400 revs when the car began to shake a bit but this seemed to be due to the wheels being out of truth which the balts run on. The crankshaft by itself is very good. 5 Very light pistons fitted, there were pistons with no tops simply guides for the rods weighed 1 lb. ea. The periods are then less in intensity but at the same speed, the engine feels nicer all the way up. 6 With various adjustments of slipper drive & with it on & off. No Difference. 7 With round spigots re-moved from the rear engine feet & the bolts slack. The periods cannot be felt, comes on immediately the bolts are tightened. 8 With jacks under the frame near the rear engine felt. This cures the boom in the body and the low speed one to 600 its vibration is then slightly at a higher speed but is not enough to boom the body, the high speed one does not seem to alter. | ||