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 in a 3 1/2 Litre Bentley after testing in France.
| Identifier | ExFiles\Box 82\1\ scan0279 | |
| Date | 20th October 1933 | |
| Y 4553n To Wor.{Arthur Wormald - General Works Manager} From Hs.{Lord Ernest Hives - Chair} c. to O.{Mr Oldham} c. to R.{Sir Henry Royce} c. to By.{R.W. Bailey - Chief Engineer} c. to Hn.{F. C. Honeyman - Retail orders} Hs.{Lord Ernest Hives - Chair}2/MJ.20.10.33. x236. Re. 3 1/2 LITRE BENTLEY. The car has returned from France and came back under its own power with number six connecting rod and piston removed. We have examined the pistons and we find that they are similar to those which we have run successfully on the bed, and similar to those which were fitted to the fifteen cars, also the same as those fitted to our open car which has run 12,000 miles. The only difference is that these pistons were given a special heat treatment. We have discussed the question of the treatment with Hy.{Tom Haldenby - Plant Engineer} and Z. and we do not believe that this has any definite bearing on the failure although it has still got to be proved. The conclusion one is forced into is that the trouble occurs when the engine is driven on the fringe of the crankshaft period. The conditions of running in France are much more severe than we could reproduce over here. Although the average run for the day may be about 55, on the early morning runs they average 65. They also have at times exceeded the maximum permissible revs. of 4500 under favourable conditions. The drivers however have sufficient skill to note that they have not been running on the crankshaft period. We have got to accept that in producing a car like the Bentley it will get under extreme conditions the same treatment as our tests in France. The piston which has failed is so badly damaged that it is very difficult to form any conclusions as regards how the fracture started. The rest of the pistons out of the engine however are in good condition. We feel that it would be a good thing to have a discussion on the Bentley piston failures because we think we may have come to the limit of the flexible design of piston and we may need a radical change in design. Hs.{Lord Ernest Hives - Chair} | ||