Need advice on engine problem!

[NWetRider]

I recently got a 99CR250. I could tell it had not been maintained for a while but I got a really good deal. Anyway I test rode it for 15 minutes, ran fine, then pulled it apart. The piston was missing about a square inch worth of material on the bottom of the intake side. I looked down into the motor and saw that below the crank a small hole was in the case (about the size of a Phillips screwdriver head where the halves meet). This explained the oil build up on the skid plate. Also the left seal is leaking and one of the reeds has a chunk gone.

I am new to 2 strokes but I’m surprised it ran OK. The bore looks fine, as do the ports. I can’t see that it needs anything done to it before I put a new piston in. There is no scuffing, gouging, discoloration, etc. The top of the piston looks exactly as it should. With all that air leaking in shouldn’t it have been super lean?

I guess I can JB Weld the small hole? Should I split the case? I’d rather not if I don’t really need to. I think the piston broke a while back, and I can’t find any pieces of aluminum anywhere so I’m wondering if any damage it did is already done? Could there be chunks hiding somewhere that could cause future damage? The crank bearings feel have no play and the connecting rod is fine. Where did the piston piece go to anyway? Anything else I can check for damage?

 

[fow350]

Hmmm, good question, where did the piston piece go? I would definately split the case and see what else is/may be wrong. You cannot see everything without splitting the case, and you have to replace the seal. As far as the hole goes, I guess JB weld would work if you are willing to check it all the time and make sure it is still there. If it were me, I would split the case, tear it down and get the hole welded up. Yes, a hole in the case would defiantely cause it to run leaner.

 

[darringer]

I would tear down the engine completely, and have the case hole welded up. Who knows what else is wrong there. I would also suspect the condition of the crank and main bearings. A complete rebuild would be a good idea.

 

[Mike R.]

Umm

and saw that below the crank a small hole was in the case (about the size of a Phillips screwdriver head where the halves meet).

Are you sure your not seeing the Oil Weep hole that is suppose to be there?
It is eactly where you describe and is 1/2 rounded right where the case halves meet.
Assuming you have a Service manual for the 97-99 CR-250 look at page 10-19 it shows a picture of it.
Also pull the pipe the lil piston piece probably got thrown into your pipe or if small enough right out the end of your silencer.