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).
Issues with push rods and tappets, proposing design changes for Wraith III & Bentley III engines.
| Identifier | ExFiles\Box 100\3\ scan0005 | |
| Date | 13th July 1938 | |
| HSH + 654 To RHC.{R. H. Coverley - Production Engineer}. from By.{R.W. Bailey - Chief Engineer} Sewell See me RM{William Robotham - Chief Engineer} c. ~~Rm.{William Robotham - Chief Engineer}~~ c. ~~Da.{Bernard Day - Chassis Design}~~ c. Rp/Swdl.{Len H. Swindell} BY.9/N.13.7.38 Wraith III & Bentley III - Tappets & Push Rods. ---------------------------------------- We have from time to time been troubled with push rods whipping and rubbing on the tubes in the cylinder head on both the Wraith III and the Bentley III experimental engines. The original design of tappet had the push rod cup located at the top of the tappet and a .250" diameter push rod was called for. On the first Wraith III engine the tappets scuffed badly due to them not revolving freely so that a number of alterations were made including inclined tappets with the push rod cup in the base of the tappet which demanded a longer push rod. We then found it necessary to increase the diameter of the push rods to .3125" and even now they are whipping sufficiently to rub the water jacket tubes in the cylinder head. To overcome this trouble we are reverting to the design of tappet as proposed for the B.60 and Phan.III engines made in cast iron with the push rod cup at the top, which enables us to shorten the push rod length by approximately 2.000" and so reduce the whipping considerably, at the same time the combined weight of the tappet and push rod is reduced by half an ounce. The proposed design is shown on E.CD.795 print attached, and we would like you to tell us when the new tappets and push rods can be introduced on the Wraith III production engines. A further modification to tappets shown, is that the tappets are vertical instead of inclined and have a flat bottom face instead of a coned face for use with narrow offset cams. These have already been tried and reported on favourably as stated in Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}1/JH.10.5.38, and as this method of ensuring the tappets revolving appears to be much less costly and equally as effective as the tappets at present being produced, we would also like to introduce this change as soon as possible without inconvenience to production. | ||