i rebuilt my friends 250R top end yesterday, its an 86. new wiseco piston gaskets etc... i've assembled several motors before but when i added coolant it just starting leaking out very badly from the bottom of the head. never seen this before. i fired the motor it ran beautifully lots of compression and sounds really strong only problem is that head leak. can anyone help me out never seen this before. is there is certain torque sequence on the head nuts? i just hand tightened them all the way down then criss crossed to tighten. he has an extra head gasket left what do you sugggest?

 

I suggest Yamaha Bond or spray copper gasket material on the stock head gasket. Search online for the proper torque spec for the head. Check the top of the cylinder and bottom of the head for any pitting or gouging they may have. Good luck.

 

Well, if it starts and runs and has good compression it doesn't sound like it's leaking in the motor. Sounds like it's the water jacket leaking externally. My lt250r head has a screw in it, that if I removed it would leak antifreeze. Since it's the highest point of the motor I assume it's a bleeder screw or something. Is there supposed to be one in yours? Have you traced it back to the source of the water?

 

Bleeder screw on a TRX250R is on the side of the cylinder, about half way down on the shifter side. Not sure why they didn't put it at the highest point.

 

I wouldn't put anything on the head gasket. Take the head back off and make sure both surfaces are CLEAN!! Scrape them w/ a razor blade, but be sure not to score the alumumum, then wipe them clean w/ brake cleaner (or any good solvent). Get the torque specs and sequence and try it again. Could just be a flaw in the gasket, or piece of crud on one surface.

 

I am assuming you used a new head gasket?
As was mentioned, take the head back off and clean the surfaces. You may need another head gasket too.

I lapped the head on both of my 250Rs prior to re-installing them (granite plate and 600 grit sand paper, using a figure 8 motion). This assured that the head was perfectly clean and flat.
Wouldn't hurt to try this with yours.

 

thanks guys it was a new gasket hes got a spare im throwing that on for him surface was cleaned and prepped eitc.. ill let you know how it turn out. bike runs so much strong now though.