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).
Failure of tappet washers and proposing a new square washer for the Phantom III.
| Identifier | ExFiles\Box 96\2\ scan0294 | |
| Date | 4th August 1938 | |
| 354 BY.3/G.4.8.38. RMC. c. Rm.{William Robotham - Chief Engineer} c. Da.{Bernard Day - Chassis Design} c. Hx. c. Mx.{John H Maddocks - Chief Proving Officer} c. BY/CS. SWDL{Len H. Swindell} PHANTOM III - TAPPETS. Referring to RHC.{R. H. Coverley - Production Engineer}12/MJ.20.7.38. the one essential point which I wish to incorporate without fail at the earliest possible moment, is the square washer E.89349 in place of the present cylindrical washer. It is quite certain that the breaking down of the bearing surface on the tappet and the cam is not due to the fact that the normal forces to operate the valve and the valve spring are over-loading the contact surfaces, that this is so is made clear by the fact that LA.{L. A. Archer} produced 63 engines of the non-hydraulic tappet type before he had any trouble, he then had three instances of failure, which means that only 5% of our product suffered. If it were overload it is quite clear that these proportions would be reversed, that is 95% should fail and 5% might just scrape through due to exceptionally accurate surfaces in alignment and optimum hardness conditions. I am certain that the failures are due to excessive loads being set up under certain exceptional conditions, and I am inclined to think that the exceptional condition is the trapping of oil by the cylindrical washer at the bottom of the tappet spring, which enters what is to all intents and purposes a rather comparatively close guide, trapping oil above it if it should happen that the surfaces have been flooded with oil, the variable factor is the effect which causes the excess of oil to be present above the washer. If this occurs then you have practically a choc-a-bloc system, and the severe indentation and grooving indicate something in the nature of a choc-a-bloc effect rather than any slight overload. One other point is that as we built 63 engines of the non-hydraulic type without experiencing trouble the only effect we can expect to produce by the introduction of the square washer is not an immediate improvement, but a complete elimination, over production of say 100 engines, of the fault in question. I wish to bring in the square washer quoted at the earliest possible moment, but not to dismantle engines for its incorporation. Will BY/CS. kindly see that the square washer is instructed. BY.{R.W. Bailey - Chief Engineer} | ||