Thursday, 22 November 2018

Gudgeon Pin Extractor

Gudgeon or wrist pins retain the piston to the connecting rod with varying degrees of clearance, transition or interference fit according to the predicted running temperature of the engine, and are retained by a circlip at each end in addition to any fit. This means that removal of the circlips will sometimes allow the pin to slide out, but more often than not you'll need to warm the piston such that it will release its grip on the pin. Obviously, belting the end of a tight pin will do your connecting rods no favours at all, so anything other than light tapping is a no-no.

A much better approach is to use a gudgeon pin extractor. These usually consist of a threaded rod passing through the pin, some means of holding the pin, a tube large enough to allow the pin to come out and a large washer to spread the load.

I made this extractor to deal with the FH gudgeon pins, which were quite tight. It is made of a bit of 1" tube, with a closed end turned from aluminium; that's M6 threaded rod in the middle. The tube is long enough to accommodate a 3" gudgeon pin.

A turned steel plug fits neatly into the gudgeon pin aperture in the piston and is reduced to just fit inside the pin such that it doesn't slop about. It's threaded M6 internally and is retained with a nut for the moment.

Here it is, set up and ready to extract the first pin:

Here's the extractor set up on the piston. The end of the tube is shaped to fit the piston, spreading the load over the piston wall:

A blast of heat on the piston crown and some steady winding are all that is necessary to draw the pin out of the piston, without placing any side load on the connecting rod. When you have done winding, the pin is neatly enclosed in the extractor:

Job done.

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