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 design and function of different hydraulic tappets, including the Pierce-Arrow and Chrysler types.
| Identifier | ExFiles\Box 173\3\ img052 | |
| Date | 3rd February 1934 | |
| WILCOX-RICH CORPORATION DETROIT, MICHIGAN EXECUTIVE OFFICES 9771 FRENCH ROAD DETROIT February 3, 1934 Dict. 2-2-34 PLANTS SAGINAW, MARSHALL BATTLE CREEK Mr. Rowbotham, c/o Detroit Athletic Club Detroit, Michigan. Dear Mr. Rowbotham: I enclose herewith assembly blueprints of several hydraulic tappets. T-1735 is the Pierce Arrow tappet. It is the first tappet of that type that we made and undoubtedly is the one that was referred to when you had your discussion with Pierce-Arrow. The small hole in the center of the plunger where it lifts the valve, is a vent hole made necessary because oil in this tappet feeds through the wall of the tappet and also through the wall of the plunger so that the reservoir from which oil is drawn when it passes the check valve really is in the plunger itself and it must be vented to allow air to escape. The present day construction which will be used on all cars other than Pierce-Arrow, principally because we think it is less expensive and because we know it functions equally well, is represented by the two Chrysler drawings T-1733 and T-1742. In that case the plunger is made up of two parts welded together and although it is hollow there is no oil inside of it. The oil is fed through the tappet wall itself into the bottom of the tappet where it is picked up by suction through the small tube and passes past the check valve into the compression chamber under the plunger. It is thought that drawing oil through a small tube from the bottom of a pool of oil is more likely to give you oil free from air than would be the case in the Pierce-Arrow tappet where the oil may be churned around pretty well without so much chance to settle without bubbles being in it, to where the check valve will allow it to pass into the compression chamber. Of course the tappet really is supposed to be full of oil when it is operating but when the car stops it may not remain full and this tube in the bottom of a rather deep pool then gives you a supply right at the start without any possibility of air getting into it. Air separation is carried out outside of the tappet itself to a certain extent as you will see from the assembly drawing. The oil is supposed to be fed into a pocket of some sort in the cylinder casting. It is supposed to drain from the bottom part of that pocket into the tappet and the pocket is vented intermittently at the top so that air can go out either when the engine is standing or when it is working. The length of accurately bored hole in the first Pierce-Arrow type is quite great as compared with the type that we are putting out now on Chryslers and that is one of the reasons why the expense of making the Pierce-Arrow type is greater than we think it ought to be. | ||