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).
Analysis of engine noise related to rocker shafts, oil pump rattle, and crankshaft torsional vibration periods.
| Identifier | ExFiles\Box 179\3\ img017 | |
| Date | 3rd April 1934 | |
| -2- No modifications have yet been carried out to the rocker shaft, such as providing an extra bearing at each end of the shafts. Neither has a stiffer rocker shaft been used so that even when the engine is thoroughly hot and the other tappets silent the ones with the overhanging rockers are still very noisy. Oil Pump. Our trouble with the oil pump rattle can we think be overcome when a pump is fitted with less backlash between the gears, the present gears have approximately .009 backlash. The present oil pump gears rattle very badly with the normal oil pressure of approximately 30 lbs/sq.in. the rattle was found to be much worse when main relief valve was removed and engine running with only 3.5 lbs/sq. in. pressure. For a trial the oil pressure was increased to 70-80 lbs/sq.in. and a great improvement was noticed the rattle being only evident for an exceptionally short period at approximately 800 r.p.m. 10 or 15 r.p.m. either way of this speed being sufficient to entirely overcome the rattle. The rattle of course is much worse when the oil is hot. A new pump is being made with gears having less backlash. Crankshaft Periods. The half torsional period of the crankshaft with the complete damper is at 1975 r.p.m., the period is very sharp and easily run through, approximately 25 r.p.m. higher or lower than this speed no vibration is noticeable. The half torsional period occurs at 2150 r.p.m. when the weights and springs are removed from the damper and at 2350 r.p.m. when the whole damper and fan pulley are removed. At the half torsional period the weights appear to impose too great a load centrifugally without having sufficient inertia to cause and effective damping. The top torsional period begins at 3750 r.p.m. and is very violent, is definitely not safe to run through, the damper feels the effect rather badly and moves violently in a fore and aft direction it appears about .100. the flywheel does not seem to be affected to the same extent as the damper. | ||