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).
Technical letter discussing engine re-boring mileages, cylinder wear figures, and cooling systems.
| Identifier | ExFiles\Box 140\4\ scan0262 | |
| Date | 20th March 1940 guessed | |
| (2) application we had in mind: we therefore abandoned application for the complete specification. Unfortunately we are unable to let you have a copy of the actual application made in 1935 with this letter, but if I am able to obtain this by the time Mr. Aspley comes up to the Works, I will then advise him of the exact circumstances of the case at that time. Re-bore mileages run by petrol engines in the hands of operators vary considerably, as you will appreciate, and depend very largely on the type of service being considered. Taking the case of petrol distributing companies, on what could be looked upon as door-to-door delivery, the cylinder wear figures are abnormal - often as high as .001" per 1,000 miles. On the other hand, on straight run, good services the wear figures are low, and we used to take a wear figure of .001" per 6,000 to 7,000 miles as a fair figure. Generally operators are not wishful of re-boring at anything less than annual mileages of say an average of 50,000 miles: this is not a set figure, but varies dependent upon the organization in existence in the various operating fleets. We are compiling a chart of such information on this subject as is available, and if it is not ready to attach to this letter on despatch, I will forward it to you under separate cover. The wear figures you have reported on the aluminium cylinder block submitted to you for examination are interesting from the fact that you say the wear seems to be progressive towards the rear of the engine. It would not be strictly true to say that this is representative of the usual results on alum: cylinder blocks, and the opinion might be expressed that this wear figure is a function of the method employed in cooling the block. On our standard range of larger engines, the water enters the back of the cylinder head, flushes round the exhaust ports and plugs, coming out at the front end of the cylinder head, and the cylinder block is cooled by thermo-siphon. Under these conditions equal temperatures should be in existence relative to the bore. In the case of the Cub engine, the water is taken into the base of the cylinder block and an extractor pump is fitted at the front end of the block. We have never taken the temperature gradient across the block, but this may have some bearing on the wear figures you have reported. | ||