Do I need to replace my piston rings if the cylindar walls are smooth?
 

Hey everyone, I need some advice...
I'm rebuilding an XT600 and I'm wondering if I need to replace the piston rings. The cylinder walls are smooth and have no signs of wear. It was not running when I bought it, so I don't know if it smokes... Can I just replace the rings and hone the cylinder without the fear of the rings not seating properly? Need some advice...

Thanks,
Drew

best thing is check piston and cylinder wear with proper equipment... but if both are immaculate probably are ok.
Anyway a visit to a workshop with piston and cylinder and a copy of service manual\Clymer with you to check wear values is the proper way to be 100%sure... without risking of opening the engine again

You will also need to check that the old rings are not worn, and still have enough spring in them. If the piston to bore fit is fine, then you need to check the rings to bore, followed by the rings to piston. sometimes a ring will wear a piston groove. You dont need to hone the bore if fitting new rings, all you need do is glaze bust them a little using fine wet and dry and lots of oil.. Clean scrupulously the bores afterwards.

So there IS an acceptable wear measurement. Cyberzar, when you say proper equipment, I assume you're referring to a micrometer? Is there an acceptable amount of clearance between the rings and cylinder wall? Thanks of the help so far. I'm at work, so I'll check this in my manual when I get home.

Drew

The bore can look fine (i.e. undamaged) but still be excessively worn or, more likely, gone oval. A check at top, middle and bottom of the cylinder, and parallel to, and at 90 deg from, the crank with a micrometer is the only way to be sure. If that checks out OK, put the rings in the bore and measure the clearance of the gap bewteen the ends of the rings. The service limits will be in the manual. Finally, as oldbmw says, fit the rings to the pistons and check the clearance between ring and groove with a feeler gauge.

To be honest, if you have stripped it down this far, new rings would be the minimum I would go for, even if everything else checks out OK.