hi, new to forum, I bought a 99 400 scrambler for a "deal" rode for a week and it died. I let it set for about 6 months before I tore it down. found a burned piston so I had it honed out and put a new wiseco piston in it. I rode it for 1 hour and it seemed to be pushing antifreeze out of the head. when I pulled the head the walls are scarred and it looks like the piston is getting burnt again on the exhaust side. any clue as to whats wrong?

 

check the compression. should be above 100 psi. check to make sure you have the correct spark plug. BR8ES NGK brand. make sure you dont have any leaks around the exhaust manifold

when you replaced piston did you replace the gaskets too? if so did you install the head gasket correctly.

 

I used all new gaskets and the correct plug. not sure what the compression is. I tightened the head to 25 foot pounds, a buddy said it should be 18 to 20, would this contribute to my problem? The only modification is the pipe, not sure what it is though.

 

the diff between 20 and 25 isn't goin to hurt anything,maybe air in system,coolant not flowing through engine well? famous head gasket?

 

the gasket set came with the piston. coolant seems to be circulating. when it quit you could touch the engine so i don't think it overheated, but it did shut down and wouldn't start back. The head gasket wasn't blown out so not sure how the antifreeze was blowing out.. the burnt place on the piston is on the exhaust side and about 1/4 inch wide .

 

Not always but usually seizures on exhaust side of piston because of air leaks,lean condition(crank seals,gaskets leaks,lean carb settings) On seizures on intake side of piston usually because of lack of lubrication (oil pump not bled,air in lines,wrong oil,etc)PLUS did you BLEED 10 mm bolt on top of head to purge air from coolant? Have had customers have seizures because of this also when they rebuilt their own top ends.

 

I did NOT bleed the air out. I don't guess I could just put it back together bleed the cooling system and everything be o.k. ??? what damage have I probably done?

 

SEIZURE from getting too hot! If cylinder wall scored,MUST either hone if not too bad OR rebore and do it again! If piston salvageable,I would install new rings and gaskets. When assembled,remove head bleed screw,pour coolant slowly in to radiator until coolant trickles from head with no air bubbles,then replace screw and top off radiator and coolant bottle. Crank and let idle until warm,then shut off. After cooldown restart and ride NO full throttle for a short time to help breakin.If cranking and running ok after this,should be fine. ALWAYS premix first tank of gas 50-1 to help with breakin procedure. Good luck opt