Dan

I've been watching your thread with some sympathy.
I rebuilt an XT500 a few years ago after it seized up due to oil starvation.
I used genuine Yammie parts throughout. The rings arrived in an unsealed box but end gaps checked out OK and I buttoned the motor up.
It smoked like hell when I started it and didnt stop. Eventually the exhaust was wet with oil. It smoked worse on the overrun even while just revving it in neutral. I stripped the head off and the piston had a small pool of oil on it.
I had many experienced people look at the motor as I changed cylinder heads, then valve guides and valves all to no avail. I had that motor out three times in a week!

Eventually someone suggested I fit just the oil ring to the piston and check what happenes when the piston was inserted into the barrell. Well it fell right through. I ordered another set of rings from yamaha and the despite a sealed box the oil ring expander just wasnt expanding the oil rings sufficiently to even vaguely scrape the bore. I carefully opened up the expander to provide more tension and the problem was solved. I have noticed that the bike does smoke a bit on startup now and I have no doubt that my solution hasnt stood up to the test of time. I have ordered a set of Deves rings (5 piece oil ring) as I have had excellent service from them in an array of motors.

This may just throw some light on your problem. I studiously conduct the "mike" test on all oil rings I install now in honour of the guy who solved the problem. The oil ring on its own should support the weight of the piston in the bore.

Cheers

Gavin