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).
Engine cold knocking, piston types, oil consumption, and cylinder bore issues.
| Identifier | ExFiles\Box 170\2\ img218 | |
| Date | 27th November 1934 | |
| -2- Cold knocking may be due to distorted bores, and is not worrying us at all with the trans-slot piston. Our bores, after years of work, are fairly round. On a new engine with cylinders cast en-bloc, we have a suspicion that the bores may be too round. Engine runs dry at low speeds to an extent where we fear the wear. we have not heard cold knocks or idle knocks hot, but this may be due to the soft rubber engine mount. Ar e doing our utmost to increase oil consumption at 50 m.p.h. and decrease it at x. M.P.H. All rings are individual cast and are very hard. They are sprung close to the limit of the iron and have about 9 lbs. expansion. All pistons are cam ground and are a very pretty job. We dream of the day when we can produce a circular ground piston which will bed itself. Making an accurate job of the cams is very difficult and involves hand stoning. Ellis has a special indicator rig for gauging cams accurate to 1/100 of a thousandth. "En somme" :- Aluminium pistons have been a success. Trans-slot pistons about 1 1/2 thou. slack cold and 7 thou. slack on the sides promise to be even better. Low oil consumption at low speeds is a trouble. Cold starting has not been a trouble. Cold knocks and hot idle knocks have not been a trouble. Power is greater with the trans-slot piston. En-bloc cylinders introduce new troubles not yet thoroughly understood. Cylinder liners are not believed necessary if piston, ring, and lubrication conditions, and shape of cylinder bores are thoroughly controlled. Wear at very high mileage is small. No accurate figures. | ||