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).
Preliminary report on tests for an overhead camshaft conversion on a 4.1/4 Litre Bentley engine.
Identifier | ExFiles\Box 113\5\ scan0170 | |
Date | 27th October 1936 | |
OVERHEAD CAMSHAFT CONVERSION ON 4.1/4 LITRE BENTLEY. We give herewith a preliminary report on the tests carried out so far on the above converted engine. At the time of this report, the tests had been brought to a standstill through the engine being smashed. It is our opinion that the breakdown originated in failure of the big-end bearing material due to so much water getting into the oil (crankcase). This in turn being due to cylinder head water leaks, when using a solid copper gasket. (1) Cylinder Head. The question of water leaks on this cylinder head, should be divided into two parts. Firstly, the internal leaks, which we say caused the engine failure. The idea of higher unit pressure, by virtue of the narrow bedding surfaces, (which we believe was the theory behind this design) does not appear practicable in view of the gasket material at present available. Secondly, there is a very serious external water leak, on the inlet side of the engine, brought about by the absence of a complete row of studs in design. (2) Expansion. - Expressed in terms of tappet clearance variation, between hot, and cold, engine conditions. The maximum variation is .004". It is interesting to note however that this maximum figure is obtained as soon as the circulating water temperature rises above 75°C. irrespective of oil temperature, or combustion chamber temperature. (3) Detonation. The audible detonation is not comparable with anything previously experienced on our cast-iron heads. The figures shown on curve s.8 (attached) are therefore misleading, although as figures they are true. By this we mean that the noise is not so metallic. It is doubtful whether the degree of detonation as shown on curve s.8 would be heard from the driving seat, although from the figures the detonation would appear to be worse than standard. (4) Exhaust Valve Expansion. This was measured by a micrometer fixed to the camshaft housing, taking a reading from the top of the valve; contact being | ||