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).
Evaporatively cooled engine performance, focusing on leaky rubber joints, cylinder cracking and liner distortion.
| Identifier | ExFiles\Box 179\3\ img103 | |
| Date | 10th March 1932 | |
| -2- Cont'd.{John DeLooze - Company Secretary} Even under extreme evaporatively cooled conditions, as long as we use our latest type water pump and larger outlet water pipes with the extra outlet from the centre of the block, we have run a Kestrel engine under evaporatively cooled conditions developing over 800 HP. with a cylinder head temperature not exceeding 120°C. Now that it has been proved that the temperature is even, the problem consists of making a mechanical joint, and if proper consideration is given to the tightening of the cylinder studs we are confident that leaks at the top joint should be very rare. This is helped by the fact that the cylinder blocks which are now being produced are wonderfully accurate as regards dimensions and heights, they are a much better job in this respect than our original development engines. Leaky Rubber Joints. - The chief reason for leaky rubber joints has been caused by the fear of cracking cylinders between the bores because of having rubbers too tight. From our recent tests on liner distortion, we believe the cracking of the cylinders between the bore was due to the steel liner distorting and bursting the aluminium, and we do not think the rubber joint had much to do with this failure. Figures of liner distortion show that the cylinder may be .007 out of round just above the rubber joint ring, and at that point the clearance between the steel liner and the aluminium cylinder was only .002". For some time now, we have been building engines in which this clearance between the steel liner and aluminium cylinder has been increased from .002 to .035". So far we have not yet had a case of a cylinder cracking between the bores when we have had this clearance. If it is confirmed that it is the steel liner distortion that is the cause of the cylinder failures then we can now fit rubbers tighter which will reduce very considerably any chance of leakage. Another reason for fitting tighter rubbers is that the extra clearance does provide a safety gap if the rubber wishes to expand. Another fault we have had with the rubbers, especially on engines running under evaporatively cooled conditions, is that the rubber joints have not been vulcanised at a high enough temperature, and that with the high temperatures on the cylinder they have taken up the form of a groove and lost their resiliency. We are now running rubbers which will stand a higher temperature, and we are running these on an evaporatively cooled Type Test which up to the time of writing this report have completed 90 hours without any signs of leaks. We consider there are prospects of producing cylinders which, if we use the right grade of rubber and the extra tightness which we now consider we can stand, will be far more reliable than any we have ever had. | ||