Can scored cylinder be reused?

[crusty1]

Lost a circlip on the top end of my kids Kx 85. There's a score that runs from the port intake to the top of the cylinder where the head meets. It's not very big, but the compression after this was like 95# because the rings were toast. So is there anyway to repair a slight score without replating? Also, how much compression is going to be lost out the top if a new piston and rings were installed? The scratch/score does not protrude above the surface of the cylinder wall: I put an old piston with rings on it in and it moves very freely up through the cylinder. I'm trying to get my kid to take responsibility for the repairs of his bike (he's 14) and he can't afford a new cylinder right now so if this one can't be used dad's going to have to pony up $$$ for new stuff. Also, any serious risks to running a ball hone through and seeing if it will hold compression with new piston/rings? Thanks. Dennis

 

[RM_guy]

If it's a vertical scratch you might be OK for a while but keep an eye on it to make sure the plating doesn't start flaking off. KX's aren't know for very good plating. The scratch wont hurt compression too bad but it will so some extent. The bigger the it is the more compression you'll loose. Think of it as a larger ring end gap. A new piston and ring with a tight gap and the scratch will have compression of a ring that is worn somewhat.

The only way to fix it is to re-plate the cylinder. Don't try to hone it out. If anything hit it with a scotch brite to clean it up. Re-plating can be done for under $200 at US Chrome. A smaller bore is probaly cheaper but you can call them for pricing.

 

[DirtIsMyName]

You can get an idea of the sealing surface by putting a new ring in the bore and line it up using a piston. Look for light passing between the ring and the cylinder.