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).
Letter from Wilcox-Rich Corporation discussing the development and benefits of a new hydraulic tappet design for engines.
| Identifier | ExFiles\Box 173\3\ img053 | |
| Date | 3rd February 1934 | |
| WILCOX-RICH CORPORATION 2. Mr. Rowbotham February 3, 1934 This entire tappet construction is just one of a lot of little tricks and points that have been developed by numerous trials and it is likely that many successful hydraulic tappets could be produced that wouldn't look like this but we have spent several years just fussing with it and seemingly we have got it down to where it is quite practical and really ready to go into production; in fact, it is in production to the extent of the number of cars the Pierce-Arrow Company make, and probably will be production in quite a large way within a very few months. We are getting encouraging reports from truck engine makers, not because the tappet resulted in quieter engines but because the clearance does not change or rather the timing does not change by reason of clearance changes when this tappet is used. The majority of our truck engines have to have .020" clearance between tappet and valve, especially if they use austenitic steels in the valves such as KE 965 which expand half again as fast as other steels. This results in a change in timing when the expansion takes place that really is objectionable and there is always the risk that someone will set the clearance up too close and the valves will ride open and then the valves will burn quickly. With this tappet no such thing can happen. The valve always seats on its seat for the maximum amount of time and better cooling of the valve is attained and we think that the pounding on the cylinder is lessened to such an extent that seat wear down in the cylinder is not as likely to take place. In fact, in the Pierce-Arrow case they considered putting rings in their cylinders but after trying the hydraulic tappet for a long period they concluded that the rings were not necessary. It develops that also some of the Stellite seated valves there is less need for rings than when the valves are not Stellited when ordinary tappets are used. Our thought therefore is that if by adding the beneficial effects of the Stellite seated valve to the beneficial effects of the hydraulic tappet, we can largely eliminate the cause of seat down in the cylinders, we will not have to use seat rings in the cylinders and certainly one cannot say that seat rings are a desirable thing in the cylinder except that they prevent the valves from seating down. They must run hotter and they occasionally come loose and they are not inexpensive to put in and in an over-head valve engine there is a real danger should one come loose and drop out. Again, on over-head valve engines, with this hydraulic tappet no special selection of materials in the push rods or in any of the other parts need be made. The rocker arm, if the designer wishes to do it, can have one to one ratio or any other ratio that he wants without giving any consideration to expansion of the parts and altogether I think the use of hydraulic tappets will smooth the way for the designer and enable him to maintain his output at any speed just in accordance with his original calculations. Very truly yours, WILCOX-RICH CORPORATION [Signature] Engineer. R.{Sir Henry Royce} Jardine V | ||