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2003 Honda 400ex

STHbongrips

By STHbongrips
in Honda ATV Forum

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STHbongrips Newbie

STHbongrips

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Ive got a few questions regarding the top end on the 400ex.

Ive had a few problems with this quad since I got it and Im giving it one last go and doing it right lol. First problem is it keeps blowing the head gasket on the left side. The first time we figured it was just worn out and we replaced it, put it back together and it happend again. my dad replaced the cylinder because it was starting to smoke. We replaced it with a used one but it looked like it was in great shape. We bought a new piston and rings and another gasket. Everything was put back together, all gaskets looks great. Piston and rings were new and we figured it was ready to go. Well I guess not, because she started smoking again and the head gasket blew once again! This time I think we have it pretty figured out haha.

It tooks us a couple trys but we figured it out....one one the head bolts on the left side was coming out even when torqued to specs. So we got a set of helicoils and are going to install those. We also got a complete gasket set and will be replacing them all. We took the newer cylinder off to check out the piston. When the head was taken off we had planned on getting it ported and polished because we thought thats why it was smoking since the cylinder was in great shape and the piston and rings were new. But after taking off the cylinder we realized it was more then that haha. The piston has to be replaced again and same with the rings. The cylinder is going to be bored out to a 40 over and getting a wiseco piston and ring set. The bolt that was pulling out will be fixed, all gaskets will be replaced the head will be ported and polished. Im hoping that we have it all right this time, but Id like some input from you guys! I have some pictures of the cylinder and piston, can anyone explain why it happend? All fluid levels were checked and they were fine!

Piston1.jpg

Piston2.jpg

Piston1.jpg.9cdef603827b5bcc3cf989d06fc8f802.jpg

Piston2.jpg.98a7f5c39135463a07d0465c7c000a59.jpg

Edited by STHbongrips
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