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).
Car preparations and modifications for racing, including engine and system updates.
| Identifier | ExFiles\Box 90a\4\ Scan238 | |
| Date | 25th May 1936 | |
| -2- Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}1/KW.25.5.36. The special high ratio rear axle gears will not arrive here until the 3rd of June and here again, unless practice shows that we are badly under-geared on the track we shall not fit them, as any testing we can give them will be very limited. Owing to the fact that the streamlining has not come up to expectations, we have managed to get approximately the gear ratio we require by fitting big wheels and tyres. As the car has to run at night with lighting equipment, we have had to make special provision for easy location of any electrical fault in the wiring, and also for working on the car in the dark. We have fitted two complete petrol spare systems so that in the event of trouble the car will not be held up. Last year in the Tourist Trophy race the car was nearly put out of the race by clutch slip owing to the sump being over-filled with oil. In the rush at the pit stop, particularly at night, it is very easy to make this error. We have therefore fitted an automatic float control oil feed to the sump, which maintains a constant 1½ gallons in the crankcase. Any additional oil required is therefore put in an auxiliary oil tank and is metered by this float mechanism to the sump as the engine uses it up. The scheme was used for three years' racing by E.R. Hall on his M.G. and he has done 1,000 miles under racing conditions on our bits on his Saloon car. We have fitted a freer exhaust system as this is allowed by the Le Mans regulations. ENGINE UNIT. We attach a curve showing the horse power available this year compared with last year's Ulster unit. It must be appreciated that though we have put up the bore of this engine, the overall dimensions remain exactly the same as the original 20/25 which was designed to give about 50 H.P. We are therefore now getting somewhat tight for valve dimensions. Our programme was to run 24 hours at full throttle, developing maximum H.P. The only fault that the test revealed was that after 12 hours of this treatment the exhaust valves began to pocket on their seats. Ultimately this means that the valve clearance has to be adjusted. From previous experience at Ulster we know that road racing conditions do not approach test bench work for severity, and it is very probable that this pocketing will not occur at all during the race. If it occurs sufficiently to cause an appreciable drop in performance, the valve clearance will have to be reset during one of the pit stops. | ||