Quote Originally Posted by trajectory View Post
Piston ring removal, Hopefully someone better qualified than me will be along to give some advice. In the meantime I think there might be something on YouTube, hopefully, have a look for servicing a Webley senior or mk11 Service air rifle as they have phosphor bronze rings. Only thing is if they are servicing them they may not remove them for re use or they might already be broken. They are brittle so in motor engineering you used to push a ring from one side & wiggle a thin shim in the gap that appears opposite, then you move around 120 degrees & repeat, then another 120 degrees till you have three shims in place holding the ring open. Then wiggle the three around till they are at 90 degree spacings, then insert a fourth one. The shims are small in width & very thin but strong enough to hold the ring open , just enough to slide off the piston. Well that's one way old cars were stripped down. Same might work for your BSA but wait till someone else gives you another idea. Maybe thin but strong plastic might be enough, cut from packing material?

BUT they are BRITTLE so research it well, & choose whichever method you think is best for you. Once broken its too late to go back. It's your decision.
Echo trajectory's advice re ring removal. Late 60's early 70's rebuilt number of villiers 2 stroke m/cycle engines as a well as few 4 strokes. Used the shim method to change the piston rings, owners manuals had v detailed info on checking piston ring wear, measure gap in bore! Quality and lubricants gave impression that wear was normal and replacement the answer. some rings had chamfered edge as wel,also oil control rings as mentioned. ring ends varied from square to angled , I recall stepped ends on one or two, as well as pegs in groves to hold in place, stepped 120 degrees with 3 rings. Very brittle and required careful handling.
If this was a 'mod' by a skilled owner, looks like good work those cutting groves on a lathe, where would the rings have come from? Pro priority ready made from another application? Or if home made takes the skills to
Changed ring in my (then) 10-15 yr old Webley senior in late 60's when acquired it, along with new spring. No reason, apart from cos I could !