So I picked up a non running bike with 28000 km from a guy I know, got it pretty cheap, ran when parked 5 years ago. Went though nd cleaned carbs fixed some cosmetic issues, serviced, checked valves, have it running and rode it 60 kms. But come to find out it has 70 lbs compression on the Rh cylinder. I have not checked the other 3 yet.

How much of the engine needs to come apart to change a piston?
Head off , but then can the piston be removed by just pulling the oil pan? How common is a cracked piston in these motors? Kind the last thing I expected to be wrong with a lower mile Honda.
I could only put 20 psi shop air into the plug hole without rolling the engine enough it opened the valves, but at 20 psi into the cylinder the only air I hear air leaking out in into the crankcase oil filler, not exhaust or air intake so pretty sure that rules out the valves.
Might be a part out coming in the near future. Bike located in Northwestern Ontario Canada