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).
Internal memorandum discussing piston rattles, experiments with increased clearances, and the performance of different piston types and lubricating oils.
| Identifier | ExFiles\Box 35\2\ scan 211 | |
| Date | 31th January 1930 guessed | |
| To R.{Sir Henry Royce} from Bn.{W.O. Bentley / Mr Barrington} To CJ. - 2 - Bnl/W22320 (Contd.) Experimental cars mentioned, the practice of increasing very considerably the clearance on the top band is not a complete cure but it certainly delays the appearance of the fault. 2-EX is the first case in which piston rattles have appeared with pistons having the increased clearance on the top band. It is not known at the moment whether "picking up" has occurred on that portion having a very large clearance at the top of the piston or on the narrow band immediately above the top ring. We are awaiting news from Nice on this point. Pistons fitted to the Bench Test Engine having a ring at the top of the piston, and this has run over 50 hours successfully. A car for road tests has been fitted with pistons having this ring at the top of the piston and also an additional ring immediately above the four standard rings. The Test Dept. have not experienced piston rattles on Test Cars and they have received no complaint regarding cars delivered. Piston rattles are at present, therefore, confined to experimental cars which are not standard either as regards engine lubricant or else as regards piston clearances. X3732 The Test Dept. reported that 33 chassis had been delivered and were now fitted with the old-type nonsplit aluminium pistons which have also of course a fine clearance on the top band. In any case these pistons will be changed for the latest split type and the large clearance will at the same time be embodied. 14 chassis have been delivered and are at present fitted with old-type split aluminium pistons, which also have the fine clearances on the top band. About 75 chassis have been delivered with pistons having our latest recommendations regarding increased clearances on the top band. In addition there are 130 chassis on test and engines built and building in the shops with the pistons in the same state. After considerable discussion of the above facts, Mr. Wormald suggested and it was agreed, that Hs.{Lord Ernest Hives - Chair} and Bn.{W.O. Bentley / Mr Barrington} should prepare a report embodying recommendations discussed. He also drew attention to the apparent importance from the evidence put forward, of different classes of lubricating oils, and the fact that our present experience with the post-war car, even with Castrol, was that engines would now run from 5 to 6 thousand miles before trouble occurred (in this case piston ( Contd. ) | ||