Expansion and Contraction of Piston Pin

Expansion and Contraction of Piston Pin Points : expansion and contraction of piston pin, importance and problems related to piston pin, problems in internal combustion engines, ic, engine In many modem engines the gudgeon pin or piston pin is made a thermal fit in the piston bosses. Thus when the piston is heated to the temperature of boiling water, the holes in the bosses expand sufficiently to enable the cold piston pin to be pushed readily to its working position.

The piston pin is usually made hollow to save weight and to give as much bearing surface as possible. The material used is a high-grade carbon or low nickel content steel, casehardened and ground to size.

Various methods have been used, in the past to secure the pin in piston bosses. Of these only with split spring ring has survived. The usual method employed in modern aluminum alloy piston is to make the pin a push fit in the small end bearing and piston bosses. It is secured against end movement by means of spring clips or with a special design of clip known as circlip this has lugs at its ends for facilitating its removal with a pair of round-nosed pliers. The circlip springs into a groove turned in the piston boss.

In certain modem designs the piston pin is centrally clamped tightly in the small end of connecting rod and allows to rock in the piston bosses. When the piston is made of high strength aluminum alloy, the floating piston pin will operate satisfactorily in this alloy without the necessity for bronze bushes.