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).
Tyre specifications, spark plug gaps, and valve & tappet clearance issues for car 22-G-V.
| Identifier | ExFiles\Box 101\1\ scan0224 | |
| Date | 24th April 1936 | |
| X77a G.W. Hancock, Esq., Hotel de France, Chateauroux, Indre, France. Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}28/KW.24.4.36. 22-G-V.{VIENNA} Tyres. Dunlops made a mistake about the tyres for this car, we asked them to give us tyres with chamfered shoulders and instead they gave us the old type 90 Dunlop tyre, the shoulders of which had not been chamfered. It will be interesting to get a mileage figurefor these tyres, but we are following out with another set having chamfered edges immediately. The point is, how much the chamfered edge will reduce road holding and life. The advantage of the chamfered edge is that it gives less tyre noise under London traffic conditions. Plugs. We find that the Americans recommend a plug gap of .032" to .035" with downdraught carburetters to get good slow running. This astonishes us. We should like to know, however, how long it takes, starting with .025" plug gaps, for the points to burn and reach the condition where misfiring sets in. We know we can get a good deal better slow running with .025" gaps than with .018". Valve & Tappet Clearance. We are not too happy about the 20/25 valves. We think that they get hotter than Bentley valves because (1) the camshaft has a long toe which reduces the time the valve can get the heat away through the valve seat, (2) there is more back pressure in the exhaust system. | ||