Its my understanding that if rings are moved( rotated) in the bore, then they are no longer seated.Theyll no longer be riding in the exact same place. If youve pulled the piston out, I think youll be reseating the rings. Not a big "Inside the engine" mechanic, tho, so youll need to wait on an answer from someone else, thats just my .02..
& I wouldnt be messing with the rings, even if I hadnt found the leak,not if it was running okay.

In past years I have rebuilt many engines, small block chevs mosty, but several MC engines, along w/ Kohler mower engines too. And I have never known to reuse piston rings. But thats probably because the rings were most times the reason for the dismantle in the first place. But I know it is not commonly done, except maybe to save a buck.

You say the rings were in good condition,.......so did you....or whoever, install a ring (off the piston) in the cylinder and check that the end gap was w/in tollerence ?

All that a loose piston will do is cause noise, (slap) as all a piston does is move the rings up and down in the cylinder. A loose piston will not cause it to use oil. But rings w/ to much end gap will not only pass oil (oil ring) but will also pass compression. (comp ring)

Did your friend use a micrometer to measure the piston & compare to specs? Did he use a cylinder bore gauge to check cylinder wear, or an inside mic. to measure bore size to determine wear? Cylinders wear to a barrel shape so only by measuring this taper can you determine what needs to be done. Are you going to break the glaze on the cyl. walls (providing it doesn't need to be bored)? Just a few of the ? I have before deciding what to do.

If you were using oil, I would replace the rings. While it's easy to check end gaps on compression rings to check for wear, I know of no good way to be sure oil control rings still have proper tension to maintain a good seal.
If it was mine & didn't need boring I would still hone the cyl. & replace the rings. I would also do a search to see if anyone offers a 'gapless' ring set. Leakdown tests on engines I've built with them typically have 2-3% leakage compared to 6-7%+ with normal rings. After a full season of races they are still 2-3% & normal rings are as much as 12%. If you are already this far into it don't cheap out now, it will just bite you in the butt later. JMO
And it might be worth it to take the piston & cylinder to a machine shop & pay them to check it for you.

Hope this helps.

BTW, I'm an ASE Certified Master auto tech. & I've built a few engines over the years.

Rings rotate on the piston ! They dont stay clocked in the same place for very long. Valve stem seals are your best bet for oil probs...

I'm going in the way of the wiseco piston for the dr650.
the stock size for a dr650 is a 1mm overbore for us.
you can get them on fleabay search 4597M* and all the sizes will pop up.  One guy has it for 126 and change.  These are higher compression pistons with reliefs for the valves.

That, a lancer cam and a super chain should do ya.  I think it'll bring the compression up to 9 but not sure.  and I'm getting the nikelsil.

BurnPgh wrote on 09/13/09 at 22:50:28:


NO you would NOT need to do a break in unless you used NEW rings and a fresh bore !

If things go well, should start the rebuild this winter.  

As far as gas goes, I maybe siphoning by brothers race car when he ain't lookin'.