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 report into failures of the 20 HP starter motor, detailing causes and remedies.
| Identifier | ExFiles\Box 40\5\ Scan195 | |
| Date | 24th June 1927 | |
| X3587 DEPOT SHEET NO. Hm.{Capt. W. Hallam - Head Repairs}59. Origin of information. Hs{Lord Ernest Hives - Chair}2/LG24.6.27. 20 HP. STARTER MOTOR FAILURES. X5650 We have been investigating the various troubles which are experienced in the Test Dept. with the 20 HP. Starter Motor. These can be placed in the following order :- 1. Sticking of pinion in disengaged position. 2. Pinion crashing on teeth of flywheel and not engaging. 3. Clutch slipping when not engaged. In investigating the first condition, we find that the failures are due to three causes - namely - cross-binding effect of the nut, climbing effect of the stop, and a slipping clutch. The sticking of the pinion is caused by a cross-binding effect taking place due to the necessary slackness of the nut on the thread. To overcome this it is necessary that the inner clutch plate D.51524 should float freely in the cover D.50872 otherwise it throws the whole unit out of truth and causes a binding. It is also necessary that the bronze washer D.57384 is free to revolve. Several cases have been found whereby the cork clutch had insufficient friction to convey the inertia of the mass of the unit, and would not run up the thread and so engage. The chief cause of this is the poor-co-efficient of friction of the cork. It does not appear to be the effect of too much oil, as the cork discs which failed were to all purposes in a moderately dry condition, similar to others which were O.K. In investigating this we found that the outer spring D.51133 was one of the minimum poundage allowed i.e. 6 lbs., and by fitting the maximum spring (i.e. 8 lbs.) it overcame the slipping and engaged without trouble. The trouble experienced with the false engagement or crashing i.e. the pinion teeth rubbing on the edge of the flywheel teeth and not engaging, is entirely due to the spring D.51133 being on the weak side. It will be seen by looking at the sketch, that when the pinion unit has climbed the thread as far as the flywheel teeth, when starter motor is in position, it leaves the pinion with a free movement of .250" and is controlled by the load imposed by the spring D.51133. If the spring is on the weak side, contd :- | ||