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 induction system, oil consumption, and main bearing performance.
| Identifier | ExFiles\Box 123\5\ scan0322 | |
| Date | 23th February 1939 | |
| -4- INDUCTION SYSTEM. The duplex system which is similar to the Buick gives good distribution in conjunction with the AA{D. Abbot-Anderson} 25 Stromberg carburetter. As previously stated, any attempts to reduce the induction pipe depression have spoiled the good distribution, but tests are being continued in this direction. A design of air silencer is required for this type of carburetter. The idling is quite good at 300 r.p.m. and anticipate that there will be a further improvement with less overlap, that is with the short inlet duration camshaft. GENERAL. The oil consumption as checked over 2 hours at 4000 RPM is exceptionally good at 1 pt. per hour, which figure can be regarded as an economical one for the normal six cylinder engine. This we attribute to the following two reasons:- (a) The consumption run was taken after 50 hrs. development running such that pistons and rings had the opportunity of thoroughly bedding down. (b) That the Vandervell main bearings in this unit are fitted with a lower clearance than our own main bearings, approximately .0015-.002 against .0025-.003) which in consequence reduces the amount of oil thrown up the bore. It is interesting to note that when S.S.V. went to France for the initial 15,000 miles test the consumption was, on the test bed, too small to measure and in parallel with the S.80 was fitted with Vandervell main bearings. Although the low clearance on the S.80 main bearings is not small enough to cause any trouble, the power has increased over the 50 hours running by 5-6 BHP indicating that a little more clearance would be an advantage. Incidentally, the oil consumption run was carried out under a main pressure of 40 lbs. per sq.in., which is rather higher than usual - 30-35 lbs. per sq.in. As received, the main pressure was low and barely 30 lbs. per sq. in., and a stronger spring is required. This result was achieved by stretching the existing K.88790 spring to 1.850 giving a load of 4.5 lbs. at 1.00". A slight leak from the rear main bearing is evident as sprayed from the flywheel and requires investigation. | ||