They are WW machine screws or set screws ( full thread on shank )
The head is milled flat on one side then inverted and milled flat on the other.
Some with a good hand could file them flat & parallel, but not me.
Then the remaining rectangle of head is ground to the 1/2 moon shape
The 1/2 moon is about 2/3 the depth of the milling in the crank case to allow them to be rotated so they line up.
So none of them were done up tight against the body in the first photo.
No my idea so no credit due.
They were done by Peter Scott Motorcycles a local magneto / dynamo workshop.
In the last photo up can see the edges of the thread machines slightly and in the shot above the pin siting on the bottom of the slot showing that the pin is shallower than the slot to allow for alignment.
Worth the effort no matter what the state of you cases is.
It was a long time ago we were talking about these pins & I thought I had some spares but they had been given to another M20 rider some time ago.
At a guess, considering that they are all within 1/12 of a turn on being fully home the bolts were most likely screwed home then the edged scribed onto the heads then removed and milled down to the mark.
The faithful M 20 is currently off the road as it did a head gasket in 2016 and when it was replaced the piston was sitting lop sided as the gudgeon pin retainer had come loose & the pin made a nice deep grove completely through the std bore liner ( bugger)
That would have happened around 2005 because it was around then it started to blow excessive oil out of the breather when pushed really hard.
Not the fasted machine BSA ever built but these old warhorses are tough and just about unstoppable ( if you have enough oil ) so the War Office did well to settle for them.
The spare engine is just about in so I will be pulling the old one down.
Got an M21 crank to go in and a 1800cc VW piston to sit on top but that is for after the international.
