This part is one of the more complex parts to make, in my opinion af there are several operations that have to be carried out and all must be accurate.

First the external size is machined with a centre in the end to hold it steady and as much of the surplus bar in the chuck as possible.

Then the piston rings grooves have to be machined. In my opinion, the groove in the piston should be slightly (say, 5 thou) deeper than the thickness of the ring, and the width should be the width of the ring plus 2 to 5 thou.

Then the end is drilled to depth and bored out to size.

Then the angled entrance is machined in. a 20 degree angle needed to make the dimension all tally ;- as far as I could see !!!

Also a note for the piston rings:-

Free gap: The ring end clearance when the ring is uncompressed.

Compressed gap: Also known as ring gap, it is the end gap measured when the ring is installed and it is likely for this engine to be about 4 thou (0.004").

That now leave the drilling and reaming crossways.

Working out how to hold the piece ready to drill etc is difficult but I have decided to obtain two larger "V" blocks to better support the piston which should make life a lot easier.

From going to the show at Warwickshire I was able to take the picture adjacent.

You can see that there is a small hole on the top marked "Oil hole". This is drill right through the piston and is in line with the "Gudgeon pin access". This should enable the little end to be lubricated.

The piston was drill and reamed to take the gudgeon pin but has not yet been drill for the lubrication hole.

The piston ring have been fitted and the brass end of the gudgeon pin are ready to fit.