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 failure on a Bensport model and the proposed solution.
| Identifier | ExFiles\Box 86\2\ scan0017 | |
| Date | 20th March 1933 | |
| X236 To BY.{R.W. Bailey - Chief Engineer} from E.{Mr Elliott - Chief Engineer} c. Hs.{Lord Ernest Hives - Chair} By/SS.{S. Smith} E.2/HP.20.3.33. Bensport Piston and Cylinder Head. We have had a piston failure on the Bensport running in France in which it is reported that the top of the piston has come right off, the fracture being a continuation of the horizontal slot for the spring skirt. As we now find this engine was fitted with a thin metal gasket before leaving for France, and the pistons were of the type which come flush with the top of the cylinder block, we believe the failure is due to the piston striking the cylinder head at high speed. It was never our intention to run with less than .050" clearance at this point, which is the clearance normally obtained with the standard copper asbestos washer, but as it is possible that customers may fit these thin metal gaskets, which are sold for sporting cars, and as we see in this case was fitted by the Experimental department, we think the only wise thing to do is to go back to the standard 20/25 piston which gives us .03 additional clearance. At the same time an adjustment of the compression ratio will be required, and this is given by the dotted line shown on the cylinder head drawing LeC. 3393. We are assured by Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} that there will be no loss of output consequent upon using the standard piston. This piston gives .080" clearance with the head when used with the standard C.A. washer, which will also be a useful safeguard should the white metal run in the big end, as in the recent failure which occurred on the J.1. engine at the Works, in which case the piston head actually shows the markings where it has been striking the cylinder head after the white metal had run. E.{Mr Elliott - Chief Engineer} | ||