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).
Analysis of an engine failure caused by a loss of exhaust valve clearance.
| Identifier | ExFiles\Box 5a\3\ 03-page038 | |
| Date | 16th September 1931 | |
| X5840 To S.R. From H.H. Hotel de France, Chatenreaux, Mexico. 16/9/31. 18.9.17. re 16.9.17. the car ran after 100 miles running yesterday as we could not maintain the clearance of the exhaust valves. We dismantled the head to substantiate the evidence of the failure. We have formed the following theory of the cause of the failure in the first place, and the repeated failures. We believe that the first symptoms are caused by the distortion of one valve, bent which destroys its seating. The valve of course gets hotter due to the less contact on the seating surface and it gradually becomes worse, the valve clearance runs partially. In conjunction with this there is a hammering effect of the valve on the seat which lessens the clearance. We could however barely scrape in the .004 feeler and large enough to take the bottom diameter of the valve. We find that with the heat of 18.9.17 the valve had hammered into the seating and wore in the bottom of the seat at one side making a knife edge. This was preventing the full effect of the valve taking place which consequently was causing the valves to become hotter and distorting them more quickly, this made them lose .004" of clearance in approx 500 miles. We have come to the conclusion that once the valve clearance has been lost, it is unpractically useless to go on giving the said valve clearance until the fault has been corrected, and either the valve wants re-grinding or the valve seat wants re-cutting. It is a question of the valve not being made to stand up for a longer time without the distorting effect taking place. On 16.9.17 they ran approx. 9,000 miles before this effect started to take place, since then they have alternately lost their clearance, and they were in a bad condition when we dismantled the head. The hammering of the valves has not been anywhere near so pronounced as we had them with 18.9.17, and in this case it cannot have been the sole cause of the loss of clearance. We send you a sketch showing the one side effect of the hammering in as we have pictured. G.H. Hancock. | ||