I recently picked up a 1978 CB400T2 ... in really good shape, except for this gaping hole in the left piston.
I was in the process of cleaning up the bike and going through all the normal maintenance items in the shop manual (props to all here who provided that essential info) and discovered the problem after a compression check (right side was 200, left side was zero). Obviously, the motor needs to be rebuilt.
My question is -- should I bother rebuilding (I've heard comments about pistons being difficult to find?) or just start looking for a replacement motor?
I'm fairly handy with a wrench; I've rebuilt smaller motors (lawnmowers, etc), done top-end rebuilds on cars, and my next door neighbor is a master mechanic -- so I'm not afraid of getting my fingers dirty. It's more a question of throwing good money after bad, and what the most cost-effective approach is for getting this bike in good running order and back on the road.
Note to self: Next time you feel like buying a motorcycle, bring the boroscope with you.