HOME and how to join Forum Open Area General Scott topics Scott piston and gudgeon pin Re: Re: Scott piston and gudgeon pin

Roger Moss

When we have pistons with worn or damaged gudgeon pin bores, it has long been standard practice to jigbore the holes oversize in one pass, so the two sides are in good alignment.
Next fit bushes in SAE 660 10% leaded bronze with a slight press fit that have been produced with outside diameter and bore concentric. The outside diameter is a light press fit and the bore is 0.6235″ / 0.6240″ Next drill and tap 2BA through the gudgeon pin boss and in situ bush. Next put slave4 undersize pin in the bore and fit brass 2BA security screws with loctite. The slave pin enables you to screw the brass screw in just flush with the bore. Next remove excess screw length. Now use a good long 5/8″ hone and finish hone the two bushes together to ensure alignment to give a free slide fit on the gudgeon pin. If circlips are to be used, the piston is mounted on a 5/8″ expanding mandrill and the grooves put in. Obviously this all takes time, but the final job is much more resistant to wear than the original aluminium bores. For this reason, I finish the bushes to the same sliding fit as the rod little end, so we have a fully floating pin which shares out the wear nicely. When you have finished, put the piston on a surface plate and clock the height of the bores both sides to confirm they are in line. Max error would be about 0.0015″ but with all the tooling sorted out, we would expect to do better than this. Hope this helps Roger