What size Rings?

History: 2001 XR400 was burning oil like a 2 stroke...did a leakdown and determined it needed rings.

So i have pulled the head and cylinder....valves are seated very well..I measured the cylinder with a bore gauge and i see that it is worn by about .05 mm, which is within the service limit of .1 mm according to my Clymer manual.

My question is: Can I hone the cylinder and put new stock rings in it since it is within the service limit? or do I need to account for that .05 wear by going with rings and a piston that are .05mm oversize?

Thanks!

You can get away with just honing it. I did this to my 250's stock bore and it used a little oil at first, but after 1400 miles it is using much less. It was right at the service limit after honing. A new tight bore will use the least amount of oil.

When you hone it, you will be able to see if there are any irregularities in the cylinder wall that require further honing. Mine required this.

It's nice to get a final clearance after honing that is at the minimum side of the standard clearance, but it's hard to find a machinist who cares enough to make that happen.

If you are sure you measured the cylinder top to bottom, side-side and front-back, and it's withing limits you can go back with stock rings and will probably not have to file for proper end gap. Is piston within limits? With that said, if it's a 2001 burning oil like a 2smoke, that's been ridden much, I would expect it to need valves, seats refaced, +1mm oversize bore piston and rings to be really "right" with long service life ahead. That'll run you $500 (parts and machine work) if you do the labor yourself. You decide, you may end up doing it twice, but the second time is always easier. :ride:

Edited by trooper8

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