1500 mile Mitaka (Yambits) piston inspection

[1976RD400C]

2 years and 1500 miles after new pistons I noticed my hot rod slowing down. Torn it down and here is what I found. The left side was running a bit hotter according to my cylinder head temperature sensors. Rings were shot, top ring on left side had a .050" end gap, right side .035". Lower rings were hanging in there ok. Left piston .0025" smaller than new, right side .0015". Cylinders have a little wear that the hone marks are gone below the intake and exhaust ports. A quick hone and I think they will be ok. Between the worn pistons and maybe a bit in the cylinders the piston clearance was at .004". New pistons and I should be ok but I'm checking them 1000 miles next time. This has at least stage II porting and gets ridden kind of hard (9500 rpm). 

[JKV45]

What oil are you running?

[1976RD400C]

What oil are you running?

Yamalube 2R pre-mix

[rodneya]

The piston with the clean top would worry me.
Are you going to go richer when you rebuild?