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).
Minutes from Conference No. 5 discussing the clearance and performance of cast iron versus aluminium pistons.
| Identifier | ExFiles\Box 18\6\ Scan033 | |
| Date | 11th September 1919 | |
| x2924 CONFERENCE No.5. Conference held at Conduit Street by Technical & Sales Depts., September 11th. 1919. Present:- Mr. Royce in Chair. " Hives " Cowen " Hallam " Platford " Hanbury Col. Barrington Mr. Northey " Spinney. [STAMP: S.D 15 SEP 1919 RECEIVED] Minute No. 1. Pistons. Mr. Royce explained that the proper clearance for cast iron pistons, namely, .001 per inch of diameter, had been departed from by Derby with the object of reducing piston knocks. The present clearance of from .002 to .003 inch was too fine and had resulted in seizure of pistons and consequent stoppage on the road. This clearance .002 to .003 must never be so fine in future. C.I pistons owing to their thin section heat up too quickly in cold weather, this fact coupled with a condition of liquid petrol in a cold cylinder results in an expanded piston running in a cold dry cylinder. Aluminium pistons being of thicker section and necessarily greater initial clearance expand slower so that they do not reach the point of minimum clearance until the cylinder is warm. With aluminium pistons there will be a minimum chance of seizure. To revert to cast iron pistons would be a dangerous policy and wrong. Mr. Royce therefore suggests that we should try using more oil when running light and do everything to improve the aluminium pistons instead of reverting to cast iron pistons. Customers should be advised to use oil with more body, such as Castrol. The good points in aluminium pistons are that the rings are a long way down and they hold gas remarkably well in addition in slow running and pulling at very slow speeds. | ||