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).
Test report on Engine Unit No. 7 after 31,800 miles, detailing performance, issues, and component evaluations.
| Identifier | ExFiles\Box 97\5\ scan0200 | |
| Date | 2nd June 1939 | |
| -2- Engine Unit No.7. 31,800 miles, new unit for 2nd. test. The smoothness and freedom from periods, maintained throughout the mileage was the most noticeable improvement of this engine over present standard. This is due partly to the flexible flywheel, partly to the further improved engine mounting and partly to the durability of the bearings. The whitemetal main bearings are in considerably better condition than previous Bentley bearings of any type, although twice the usual mileage has been covered. The 7-1 compression raised crown pistons have given a useful increase in performance. The test showed that there is an increased tendency towards detonation with carbon formation and changes of fuel. A governor curve has been developed and instructed which will give the minimum loss when retarded to stop detonation and a vernier control on the distributor has been called for as soon as possible. Misfires on pick up occurred on each occasion that the plug points burnt to over .030", with the R.R. distributor. It has been proved that with the Delco the plugs can be run longer before mis-fires occur, owing to the better make-break ratio with two breaker arms. The means of adjustment for the timing is very difficult with the R.R., but extremely simple and effective on the Delco. The vernier adjustment which we have called for on the R.R. has been available on the Delco for some years. In spite of these advantages the Delco remains less costly. The plugs used were Champion L.B.8. Two covered 26,300 miles without giving any trouble, after which the insulators broke; the other four were still serviceable after 28,800 miles. These results are most satisfactory, and with the higher compression ratio now used the use of a suitable plug becomes increasingly important. The results with K.L.G. plugs and 7-1 compression on experimental cars have been less reassuring and we therefore recommend the Champion, pending further test on both makes. The automatic starting carburetter as instructed for production was open to various criticisms, but in all cases supplementary manipulation of the hand throttle gave satisfactory results. The starting carburetter has been improved considerably experimentally and some of the improvements were run on this car for the last 16,700 miles. Development work is still in progress, and the scheme will be finalised and instructed for production as soon as possible. | ||