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 to Wellworthy Ltd. discussing piston ring clearances and oil consumption issues for Bentley and 25/30 engines.
| Identifier | ExFiles\Box 148\3\ scan0155 | |
| Date | 1st September 1936 | |
| X1258 Exptl. Dept. Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}8/KW. 1st September, 1936. Messrs. Wellworthy Ltd., Lymington, Hants. Dear Sirs, In reply to your letter of the 24th ult., with regard to piston ring clearances on the Aerolite piston as used in the 4¼ litre Bentley. in the first place we agree that the vertical clearance is only .001-.002". Actually the drawings call for limits of 0-.0025", which is of course ridiculous to entertain working to the low limit, but as the pistons and rings are received, there is a definite clearance of .001-.002". You say that the most efficient clearance is from .003" minimum to .004" maximum, but the point is as follows. We are definitely more troubled by oil consumption on the 25/30 than on the Bentley, which we know is partly due to the split skirt piston of the 25/30. In the latter case, however, we are already working to .0025-.0035" clearance, which is practically your ideal recommendation. In connection with the clearance behind the rings, we cannot understand your remarks with regard to the R.R. pistons as not having sufficient clearance behind the rings, as from the drawings the minimum diametrical clearance is .020" and the maximum .050". We will, however, measure up the particular set of R.R. pistons which you fitted with rings for us, as during the consumption run one of these pistons seized, which is unusual. Irrespective of what the existing clearance is behind the rings, the pistons were sent to you to be fitted with rings, in which case we understood that they would be given the most efficient clearances from your point of view. | ||