CR250 Engne Rebuild Questions

[cmack]

I have a 99 CR250 that I've had for about 8 months. It's got about 40 hours on the Wiseco piston that's in it now. I had it out last week, and I noticed that it had significantly less compression and had stalling/restarting issues when hot. I pulled the head today, and noticed smashed debris on the top of the piston and a long scratch on the right side of the sleeve. I'm guessing it's going to take both a new piston and a replating at the least. Before I tear the cylinder off, I have a few questions:

The head has impressions/roughness in the inner ring (squish band) from the debris smashing between the piston and head. The outer ring where it mates against the gasket is fine. Can I resurface the inner ring, and how would I go about doing it, or will I need a new head?

I'm not sure what caused the debris, or if it is still in my lower end? Am I going to have to do a full tear down, or is there an easy way to clean out small debris from the lower end?

Thanks,
Craig

 

[dirt bike dave]

It's gotta be crushed bearings. Pull the piston off and check the wrist pin bearing. If it is intact (it probably will be) the debris came from somewhere else. Probably a crankshaft bearing or a big end bearing. If so you are looking at splitting the cases.

The good news is that OEM Honda crank assemblies are relatively cheap ($170 or so at Service Honda; includes an assembled crank, rod and big end bearing). A piston and top end kit will run about $120; complete gasket set about $70, crank bearings about $30-$35 each, misc. stuff another $20 or $30. Any head or replating work is gonna add some more $.

If you are not comfortable splitting the cases and doing the reassembly, you can probably find a shop to do it for about 3 to 4 hours of work if you remove the motor and reinstall it yourself.

 

[AsheyYz250]

If they are small you might be ok....but i wouldnt know without looking at it.....I would look at the wrist pin bearing like he said....but I would def do a full tear down anyway....I had one do that and the needles and parts of piston ended up all the way in the crank bearings and bottom of the case.