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).
Investigation into the failure of a Fabroil idler gear, possibly due to material ageing, on chassis g-AZ-172.
| Identifier | ExFiles\Box 96\1\ scan0394 | |
| Date | 10th June 1939 | |
| W/S. (c). 361. BY/SB.{Mr Bull/Mr Bannister}1/G.10.6.39. c. BY.{R.W. Bailey - Chief Engineer} c. Rm.{William Robotham - Chief Engineer} c. Mx.{John H Maddocks - Chief Proving Officer} c. Hd.{Mr Hayward/Mr Huddy} Handwritten: F.J.H - Is this No 19/6. Rm{William Robotham - Chief Engineer} 19/6. Close grained material CHASSIS NO. g-AZ-172. SIR NORMAN WATSON. Further investigation of the failure of the Fabroil idler gear on this car points to the probability that the material of which this particular gear is made is unreliable mechanically, and may deteriorate by 'ageing', since both the gears which failed were in 'A' series, although the mileage was not high. As there was no evidence of seizure in the auxiliary drives of either engine, we have had to conclude that the primary cause of the failure was due to breakage of a portion of one tooth through fatigue or ageing, and this piece got bedded in the teeth of the camwheel, producing a high resistance or wedging action once per revolution of the camwheel. Since there is a 'hunting' tooth in the idler gear, that is, it does not engage with the same tooth at every revolution, but only once every 60 revolutions, it accounts for the peculiar wear which took place during the period of failure. In view of the foregoing, it is becoming increasingly important to find out what effect ageing has upon this type of gear, so that we shall know what to expect on cars in service. We are therefore putting in hand tests to determine the torque required to strip the teeth on:- (1). The portion of the two damaged gears which is still intact. (2). A gear which has run 30,000 miles satisfactorily except for slight wear. (3). A new gear of this type. (4). A new gear of the fine grain type which we are using for replacements. One other possibility is that the worst condition for stressing the idler teeth is produced at low speeds due to crankshaft oscillation, i.e. during the period of timing gear rattle which is at about 30 m.p.h. As both cars appear not to have been driven hard, in fact we know Sir Norman Watson's car has done at lot of running lately at 30 m.p.h., it lends support to this view, in which case the position is much more hopeful since the trouble will be confined to a few cars running under similar conditions. BY/SB{Mr Bull/Mr Bannister} | ||