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).
Piston ring fitment issues and proposed clearance adjustments for 25/30 HP & 4 1/4 litre Bentley engines.
| Identifier | ExFiles\Box 105\2\ scan0225 | |
| Date | 18th February 1936 | |
| To By.{R.W. Bailey - Chief Engineer} c. to E.{Mr Elliott - Chief Engineer} c. to RHC.{R. H. Coverley - Production Engineer} x536 Hs{Lord Ernest Hives - Chair}/Mths.{Reg Matthews}5/KW.18.2.36. 25/30 HP. & 4 1/4 litre Bentley Pistons E.60632. We now have a set of these pistons in a Bentley unit and have had trouble with the rings being too close a fit in the grooves. The rings were apparently free when the pistons were first fitted but the grooves had to be eased to allow the rings to slide freely. After running light for approximately 2 hours the rings were found to be very tight in grooves and were scored badly in places. From the limits on the drawings of pistons and rings it is possible to have both ring and groove the same dimension, and in the other direction a maximum clearance of .0015". It would appear that we ought to leave the dimensions of the rings as at present and increase the dimensions of the grooves by .001", this means that the compression ring grooves will then be .101 + 1 and the scraper ring groove .173 + 1. This will allow a minimum clearance of .001 and a maximum of .0025". The majority of Aerolite pistons we have tried have clearances of .0015 to .002". Hs{Lord Ernest Hives - Chair}/R.Matthews. | ||