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 testing, focusing on clearance increases, collapsing, and comparing split type with ram type pistons.
| Identifier | ExFiles\Box 77\3\ scan0023 | |
| Date | 11th November 1919 | |
| Contd. -7- It will be seen that the minimum clearances have increased on the average .002" during the run. It is very difficult to say how much of that is wear and how much is the piston collapsing permanently. We consider most of it is due to the piston taking a permanent set but in consideration of the severeness of the test we do not consider this is serious. We have tried the engine for knocks when starting up cold after this run, we could not pick out any distinct knocks. The fact that the pistons which only ran 25 hours at 2000 R.P.M. have increased their clearance to the same amount as those which ran for 105 hours, leads one to assume that it is the pistons taking a set when running continuously under maximum power and maximum heat. Altogether the Test Dept. have now fitted nine sets of split type pistons. One car fitted with split type pistons has run 400 miles on the dynamometer at various speeds full throttle and 400 miles on the road. We have examined the pistons and find them in excellent condition (they are the low compression type). Another car has run 800 miles on the road fitted with low compression pistons. These we have examined and find them in excellent condition. We have not yet had a case of any pistons knocks even when starting up cold on the split type pistons and there has been no seizures. From the results of the tests on split type pistons we consider that it is quite safe to use these pistons until we have proved the ram type pistons. They are the only type of aluminium piston which we know of at the present moment which will fulfil the Sales Dept. demand i.e. no knocks at all at any temperatur EH. | ||