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).
Engine characteristics, performance, and an analysis of a big end bearing failure.
| Identifier | Morton\M16\ img010 | |
| Date | 18th April 1928 guessed | |
| - 3 - The over-run is very smooth. It has four solid engine feet, on the bottom half, and the crankcase is evidently intended to stiffen or steady the front of the frame. The ratio of rotating weight to re-ciprocating weight per crank is about 10 times what we are used to, and the crankcase is extremely stiff, both halves. The car I have is known as the 'Full Grand Prix' type; there is a plain-bearing edition of it known as the 'Modified Grand Prix', with only three main bearings, which is astonishingly rough, and hardly recognisable as an 8 cylinder engine at all. C.T.V. There is a main period at 4500 R.P.M. and a very slight period under power at 2250. No others are detectable. No damper is fitted. The R.P.M. of these two periods has not been affected by stripping the shaft and reassembling it again. The flywheel is really only a casing for the multiplate (steel and cast-iron) clutch, and is only about 9" diameter, and very light. The node would probably be about a third of the way up the shaft. Big End Bearings. I had one of these pack up, which is the reason why we pulled the engine to bits. The firm very kindly paid the cost of stripping and re-assembling of the crankshaft and crankcase, and I paid for the new bits, made by RHC.{R. H. Coverley - Production Engineer} When examined, it appeared that the rollers (Hyatt type) had broken up, and smashed the bronze cage as well. Three other big ends had one or more broken rollers. The rollers appeared to be of a very weak design, and we made a complete new set merely hollow, i.e. omitting the spiral groove, together with C.H.N.S. cages, lightly hardened instead of bronze. The big end eyes are very stiff, and evidently intended to remain circular. Lubrication is via the oil jets shown. We have subsequently come to the conclusion that these rather fragile looking rollers are put there intention-ally, to be the weakest link, in the same way that we use white metal. In the event of trouble (e.g. oil shortage) they would crumble up, and save a broken rod which might wreck the engine, or avoid straining the expensive crankshaft and case. It is not so difficult to "re-metal" the big ends occasionally by cleaning up the pins and rods and fitting oversize rollers. I hope to be able to send you further information about the car when available (as various bits pack up.) Rg{Mr Rowledge}/Tsn. | ||