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).
Report comparing the performance of different cylinder heads and experiments to resolve engine 'running on' issues.
| Identifier | ExFiles\Box 124\2\ scan0286 | |
| Date | 17th December 1940 | |
| - 9 - Rm{William Robotham - Chief Engineer}/Wym.{G. Harold Whyman - Experimental Manager}2/RH.{R. Hollingworth}17.12.40. From all these tests it will be seen that the EB.3844 head at 6:25:1 comp ratio is the best head for all round performance, because although we lose the equivalent of .006" tappet clearance as compared with Exs.1383 head, it has definite advantages in engine smoothness, lack of detonations, and is not too prone to "running on" after switching off. To obtain an absolutely fair comparison of both types of cyl. head, it was necessary to try them at the same compression ratio, which it was decided should be 6.45:1, and after an interval of 11 months (due to the difficulty at present of getting new parts made) this we have been able to do. The tests have been carried out on 9 B.V car. This car has engine unit B.60 No.3 fitted with flush top pistons which raises the comp. ratio to approx. 6.6:1. Apart from anything else we have proved conclusively that the Exs.1383 head is not comparable with EB.3844 for engine smoothness, and we have no alternative but to recommend our continued use of EB.3844 heads. As there is such a marked difference in the smoothness of the 2 heads, it might be still worth while looking into the possibilities of further improving EB.3844 in this direction. Both types of cyl. head at 6.6:1 comp ratio are suffering from the disease of "running on" after switching off, and this is a problem for further investigation. We have proved that the Cast Iron engines are worse for this feature than our previous Alum engines. On 9 B.V car we have tried the following experiments without effecting any improvement whatever :- 1. Sodium filled valves of standard dimensions. 2. Increased the number of water holes in the cyl. head gasker to correspond with the holes in the head. (Some of the holes in the gasker had been deleted to Rm{William Robotham - Chief Engineer}/SWDL{Len H. Swindell}'s personal instructions). 3. Thermostat removed from engine, allowing water temp. to run at 70° C. (Continued) | ||