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).
The testing and development of piston rings, including L-section types, to improve engine oil consumption.
| Identifier | ExFiles\Box 144\3\ scan0107 | |
| Date | 11th August 1936 guessed | |
| -3- They are slightly different in the respect that the sides of the Phantom ring (E.73287) had a .002 taper, whereas we have left the rings with a normal straight side. These were an immediate success and on a particularly bad test bed engine which was only doing 150 miles/gallon, the figure was raised to 400 miles/gallon on the first run. This figure was maintained from the start up to an equivalent of 1,000 miles running. Intermediate half load tests were taken which showed the rings to have the right characteristics by further improving the consumption to 550 miles/gallon. The effect of machining the L section reduced the ring wall pressure from standard at 12-14 lbs/sq.in. down to 5-6 lbs/sq.in. and further investigation on pressure effect with an L section ring will be tried which necessitates an alteration to the ring grooves. In confirmation of the bed results GAE-20 was fitted up with both compression rings of L section and the consumption on the first run came out at 1425 miles/gallon as against 390 miles/gallon with standard rings or approximately 250% improvement. One disadvantage noticed with this arrangement on the bed is that there is an excessive amount of crankcase back pressure caused by blow past the rings. This causes loss of power, leaks past the fan pulley rear main bearing and an increased amount of oil going into the air intake via the breather. Such a condition cannot be passed and with this in view a test was taken with a standard top compression ring and an L section second ring. This overcame the back pressure trouble which was no more than standard and resulted in an improved oil consumption of approximately 125% over the standard conditions and as checked on 21-C-IV, from 360 miles/gall. to 914 miles/gallon. This is our recommendation for improving the present production cars, 22-C-V now being tested in France is having pistons fitted with an L section second ring in order to get its behaviour over long mileage when driven at high averages. | ||