Gudgeon pins.... What I hear you ask is there difficult about making Gudgeon pins
Gudgeon pins are normally hollow. The hole through the gudgeon pin is termed a long hole (depth of cut relative to the diameter of the drill) .... this means that there is a good chance that the drill will get bored and start going for a wander on the way through leaving one end with the hole off centre
This is not really a problem except that on the ends of the pin goes two little brass caps to prevent the bore getting scored if the pin moves. If you try turning these caps out of 6.35mm bar stock they will be off set
Where the Gudgeon pin is 6.35mm diameter I have chose to make the caps out of 7mm brass (= a scrap size that was found in the drawer). Initially the brass is centre drilled and then turned to be a press fit in the Gudgeon pin. I know the drawing doesn't show it being drilled but if you try pressing the two end caps into place without the hole you will end up with trapped
wind air which is going to get hot when the engine runs (assuming the engine actually runs
) and push the caps onto the bore of the cylinder
These caps need to be a good fit in the gudgeon pin but be warned if you drill after turning the brass will grown and it will not fit the pin
Once parted off these little caps might seem like they will be difficult to hold but we are going to press one into each gudgeon pin, turn the pin to size and complete the drilling holding the gudgeon pin in a collet chuck. then fit the other cap and repeat the turning and drilling. the drawing shows these caps as square
they need to be domed, this is because when the pin goes into the piston the shape of the piston is curved and by the time you get the gudgeon pins in the edge of the brass cap would be proud of the piston skirt.
The two pins with caps have both been drilled (and the inside de-swarfed
) the only other thing I should mention is that the gudgeon pin hole in the piston was reamed with a hand reamer: as you know hand reamers have a taper and on the pistons we want one pin hole slightly smaller as it will lightly hold the gudgeon pin and stop it from moving around
Jo