Gudgeon Pin Locations \

$Gudgeon Pin Locations \$ i-. ,. I “* -.. ,, * o prevent damage to cylinder walls, the gudgeon pins of T an engine must be located Gudgeon against axial movement or pro- vided with soft end wads to avoid unprotected contact-which, in the \ case of a mishap, produces score marks or grooves resulting in loss Pin of compression and power, to rectify which either reboring or sleeving is necessary. Depending on the constructor’s ideas and what may be most con- Locations venient, a gudgeon pin can be fixed in the piston with the small end of the connecting rod forming the bearing; or the pin can be fully By GEOMETER floating with bearings in both connecting iod and piston; or again, it can be fixed in the connecting rod tab-type locking washer. This type with bearings formed in the piston of gudgeon pin must always be below bosses. the side of the piston, when, for A tied-in-the-piston gudgeon pin testing, the latter is oscillated by hand is generally located by a screw, as at on the pin and pushed side to side A (left) and may be used on industrial for the bosses to abut to the con- engines and models. One boss of the necting rod. piston is drilled and tapped, and An arrangement where a gudgeon the gudgeon pin drilled to accept the pin is located one way and protected parallel turned end of the screw. In the other is as at D. The piston bosses the larger sizes of application, the are of different sizes and the pin , screw head can be drilled for a split stepped to suit, the larger end carrying pin, which prevents unscrewing by an end wad. Such a pin can be used contact inside the piston skirt. In on a two-stroke engine with an inlet small sizes, the screw may be slit at port in the cylinder wall., the smaller the end and the legs opened inside end of the pin being adjacent to the the hollow gudgeon pin, using a small port, over which it will pass, and screwdriver. the larger protected end traversing the A fully-floating gudgeon pin may plain cylinder wall. PIN be either located or protected at the To provide a piston with circlip ends. When the pin is located, the grooves, a mandrel can be machined piston bosses. are machined with in the chuck, and the piston pushed grooves for circlips, as at A (right) on, as at E, to be machined with a which obviate endwise movement. boring tool. Car and motor-cycle When the pin is protected, it carries pistons usually employ circlips as at pressed-in light-alloy ehd wads, as at B (right), and the grooves to take them B. In the case of circlips, the gudgeon are square-sided. Small pistons, pin should fit closely between them, however, can be fitted with circlips and with end wads, the pin should from coils of spring wire, one end u BORING fit comfortably in the cylinder-in turned in to handle with small pliers. TOOL each instance considerable endplay For these, the grooves should be MANDREL being avoided to guard against any rounded and slightly more than semi- suggestion of hammering which could circular. disturb a circlip or allow a protected Gudgeon pins should be a light pin to cause a tapping noise. interference fit in alloy pistons, and a A fixed-in-the-connecting-rod gud- thumb-press fit in bronze bushes. geon pin has a central groove, either Bores in pistons should be reamed continuous or tangential, as at C. when the pistons have been heated in A setscrew in the small end of the boiling water or hot rags; for fitting connecting rod intercepts the groove gudgeon pins, both pistons and pins for endwise location, and has to be should be similarly heated. For completely withdrawn for fitting or removing pins, an extractor can be removing the gudgeon pin; it must made, as at F, using a flexible band also be tightened firmly for clamping. attached to a block tapped for a The setscrew may be fitted with a pressure screw. El 11 JULY 1957 45 MODEL ENGINEER.

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