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).
Letter discussing 'constant clearance' aluminium pistons proposed by Aluminium Manufacturers, Inc. for testing.
| Identifier | ExFiles\Box 48\1\ Scan150 | |
| Date | 24th March 1921 | |
| Mr. Nadin Mr. Bagnall. Mr. Hulley Mr. Southern. OY10/G24.3.21 March 24th. 1921. Mr. Claude Johnson, Managing Director, Rolls-Royce Ltd. London, England. Attentoon Mr. Royce and Works Committee. Dear Sir, RE PISTONS. We have recently had an interview with the piston engineer of the Aluminium Manufacturers, Inc. and have arranged with him to produce, free of charge, a set of their "constant clearance" aluminium pistons for our test. The pistons they make will be quite similar to our own except that they will omit the longitudinal gash in the skirt and instead will substitute a transverse slot through the oil groove below the scraper ring on the pressure side as well as on the non-pressure side of the piston. This is the basic idea of their standard piston design and appears to us to be so sound that we have put through our shops here a set of pistons with two transverse slots and without the longitudinal slot. These pistons will have the standard .002" clearance on the big diameter of the skirt and .010" on the small diameter of the skirt. The Aluminium Manufacturers, Inc. have made several hundred thousand pistons of this type and have fitted them to all grades of cars. Particularly, they have equipped the Cole 8-cylinder car with these pistons for four years or more with satisfactory results, both as regards knocking and over-oiling. The theory which they give to account for the good running of these pistons is that the head is only connected with the skirt in the plane of the gudgeon pin and is entirely separated from the skirt in the plane of the fitting diameter, so that expansion of the piston head tends to expand the skirt only in the plane of its smallest diameter and therefore to contract it in the plane of its largest diameter. From their experiments they estimate that the piston head will run at temperatures at about 600 F.{Mr Friese} while the skirt contd:- | ||