OK tore apart the KTM

Looks like it overheated like I thought and the piston seized. So now I ordered the Wiesco pisont, ring, bearing, gasket kit, and sent the cylinder to get bored and replated. Stealer charged me $390 . Is this high? Also there is the matter of the coolant leak. The was very little coolant in the bike when this happened and I filled it before I left so it is leaking somewhere. I think its internal because I didn't notice any visible signs. Any ideas? I don't wanna throw all this stuff back on and have it overheat again. I hope maybe with all the new topend gaskets it will solve the issue but is there anywhere else I can check for coolant leak???

Originally Posted by ucfmotorcycle1

Looks like it overheated like I thought and the piston seized. So now I ordered the Wiesco pisont, ring, bearing, gasket kit, and sent the cylinder to get bored and replated. Stealer charged me $390 . Is this high? Also there is the matter of the coolant leak. The was very little coolant in the bike when this happened and I filled it before I left so it is leaking somewhere. I think its internal because I didn't notice any visible signs. Any ideas? I don't wanna throw all this stuff back on and have it overheat again. I hope maybe with all the new topend gaskets it will solve the issue but is there anywhere else I can check for coolant leak???

Pressure check the system for leaks. Most auto shops have a tool that you apply a small amount of pressure and watch the gauge to verify the system. The only question is an adapter to fit your system and I bet they can handle it.

Oh yeah I should have thought of that . Anyway I think it is leaking into the tranny because the gear fluid is nasty and I just changed it. I'm not too familiar with dirtbike anyone know which seal is that?

[G-Force Junkie]

Sounds like a water pump seal. $390 for the wholething, or just the replate? I know places to get it replated for about $175 like Melinnuim, US Chrome, Poeton, etc.

$390 for all the parts listed (piston, ring, bearing, gasket kit, and replate). I have also been looking all over for a shop manual for the thing and can't find it. I hope the water pump seal comes with the gasket kit.

[G-Force Junkie]

Originally Posted by ucfmotorcycle1

$390 for all the parts listed (piston, ring, bearing, gasket kit, and replate). I have also been looking all over for a shop manual for the thing and can't find it. I hope the water pump seal comes with the gasket kit.

Doubt it, probaly just a top end gasket set. If its that old, make sure they pressure check it to make sure the cases arent leaking either.

No I bought the complete gasket set and I am working on it myself. I am pretty good with mechanics just never worked on a 2 stroke dirtbike before.

Oil and water will not mix so if you have water in the crank case it should be fairly evident. If you indeed have water in the crankcase you will need to purchase a couple of parts to make the repair. Number 1 task will be to get the impeller out/off the shaft. Not sure on the KTM300. My 500's have a seperate impeller shaft onto which the impeller threads. When you try to remove the impeller it usually fails and strips out and you end up replacing the impeller shaft and impeller then if I recall correctly there will be 2 seals separating the water and crankcase. They usually have a weep hole drilled between the seals that will leak water if one of the seals is compromised.

However, you could still have a crankcase air leak as this can result in a very lean condition and get a similar seize. In either case, pressurized testing is the trick to identification. The cooling system being the easiest to test.

On another point, make sure who ever bores your cylinder knows that you are putting a wiseco piston in as the forged piston and plated cylinder wall have dissimilar expansion rates and if bored too tight, cold seizing can result. Check Eric Gorr for pricing on top ends as he is one of the best in the business and seems very fair in the pricing vs service category.