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).
Analysis of a broken piston from chassis B.100-GA, discussing material composition and potential improvements.
| Identifier | ExFiles\Box 90\2\ scan0073 | |
| Date | 24th May 1937 | |
| w/s (c) c. Rm{William Robotham - Chief Engineer}/Mts. BY.9/G.24.5.37. 261 HTHS See me Rm{William Robotham - Chief Engineer} CHASSIS B.100-GA. GEOFFREY SMITH, ESQ. RE: BROKEN PISTON. ----------------------- C.5/G.22.5.37. Referring to the piston which failed in Mr. Geoffrey Smith's car, Mr. Brooks' visit brought up nothing conclusive as to the cause of the trouble. From their examination of the material they could find no particular fault with the structure of same, a fact which was confirmed by our own Laboratory. The only criticism our Laboratory could make was that the magnesium was on the low side, although being still within the limits. This would slightly reduce the 'hot strength' but does not in my opinion have any actual bearing upon the cause of the failure, as we must undoubtedly have received other pistons in the large number of deliveries which have been made, which in a similar way are on the low side of the specification. The reduction in 'hot strength' would only be a small percentage, possibly 5% or 6%. With the object of getting some further information, I have asked the Experimental Department to provide me with a piston from one of their engines which has done 30,000 miles, we would then make a comparison with the material of the piston that failed, both from the point of view of analysis and general structure. I do not, however, expect to find anything startling when we are able to make the comparison in question, as the faulty piston appears to be quite good from this aspect of the matter. There was one other point, however, which occurred to me, which might have some bearing upon the subject, viz. that the reliability of the piston might be improved somewhat by specifying an increased length of time for the low temperature heat treatment, but even this view is more or less nullified by the fact that all pistons supplied by Light Production Limited for the Bentley cars have had the same heat treatment viz. no change has been made in this particular direction during the whole time we have used Light Production (Aerolite) pistons. My reason for considering that we might improve the piston by giving a long low temperature treatment was based upon the idea that very fast drivers, like Raymond Mays, E.R.Hall and others, who have not had failures, might get their pistons considerably hotter in their normal usage of | ||