Self-Adjusting Tappets

Poverty Bay Herald, Volume LXVI, Issue 19919, 22 April 1939, Page 11

Self-Adjusting Tappets

TN modern engines, the correct acl- ■* justment of the valve tappet clearances is a matter of some importance, but with the current idea of building np the mudguards so that the engine sides become rather inaccessible, tappet adjustment is not altogether easy. Partly for this reason, and partly to make an engine as efficient as possible, designers have been paying considerable attention to the production of self-adjusting tappets.

The ball was set roiling by an ex pensive American model, which use self-adjusting tappets operating on hydraulic principle, and recently i England there was produced a simple design which is available 'for two c England's most popular light cars.

The tappet combines a light c:: spring and a coarse strew thread and it „s set with the spring und-c full compression to give a clearanci of .025 inch. When the iiead is released after this adjustment, the- cc:

spring winds the head up en V.: screw thread so that the whole clear ance is eliminated. But if the valv. stem expands under heat, the tappe head will at once move down tli. appropriate aircunt on the screv thread. Thus, there never is an: actual clearance, and the valves operate with complete quietness. An ingenious arrangement of spriiv steel discs on the top of the tappe head prevents too early opening o the valve until the tappet has move. up the amount allowed for by tlv: designed clearance of the standarc tappets.