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Senior Member
Rebuilt the engine from the crank up. Its been running great, until last weekend. The bike developed a small head gasket leak between the cylinder and the head on the side opposite of the timing chain. As a testament to these engines, its still runs... I've ordered a new head gasket, and won't be able to touch it until the weekend, but I'm curious if maybe the nut tightening the head down loosened a bit allowing the leak. Has anyone out there had this issue?
2000 KTM 300 EXC (two stroke heaven)
1999 Honda 400EX
Bored to a 406
Lonestar carrier
CRF450 timing chain
1994 Suzuki 250F
Registered User
usually the stock head studs pull out of the cylinder..its VERY common with 400ex's once they have been rebuilt. Contact GT thunder and send your cylinder there and they will install HD studs and its only like $150 with labor. and you'll never have another problem. Chances are if you don't get the HD studs it will just keep happening. Ive seen is so many times.
- 05 450r-
October 2012 QOTM
Money was never a big motivation for me, except as a way to keep score. The real excitement is playing the game. -Donald Trump
Senior Member
I too was thinking a head stub may have come loose. I won't know until the weekend when I have some time to work on it.
2000 KTM 300 EXC (two stroke heaven)
1999 Honda 400EX
Bored to a 406
Lonestar carrier
CRF450 timing chain
1994 Suzuki 250F
BBBRRRAAAPPP
Agreed, probably a head stud. First time I rebuilt I did them and wouldnt have it any other way.
Also are you using quality gaskets? Either OEM or cometic MLS?
If it's stupid, and it works, it isn't stupid. - Murphy's Law
2000 426EX,sold
2004 450R WIP
-Longtime A.A.D.S. (Accessory Acquisition Disorder Syndrome) sufferer.
400EX Frequently Asked Questions, CHECK HERE FIRST!
Senior Member
cosmetic gaskets. Its a very small leak, so I'll betting a stud. I'll know more this weekend.
2000 KTM 300 EXC (two stroke heaven)
1999 Honda 400EX
Bored to a 406
Lonestar carrier
CRF450 timing chain
1994 Suzuki 250F
Registered User
get ALL 4 studs replaced with HD studs. Dont just put a new OEM stud in.
- 05 450r-
October 2012 QOTM
Money was never a big motivation for me, except as a way to keep score. The real excitement is playing the game. -Donald Trump
Registered User
I have cut the top off the nut to get mine tight. I also have had my cyl. O-ring that helps with the 12 to 1 and up builds. my bike has 13.1 comp with nos on it and we do not have HD head studs.
Registered User
CoolSounds like a hackjob.
- 05 450r-
October 2012 QOTM
Money was never a big motivation for me, except as a way to keep score. The real excitement is playing the game. -Donald Trump
Senior Member
Well I finally had a chance to tear the engine down. I found 3 of the 4 nuts holding down the head loose. I couldn't believe the engine would still run. I pulled the head to check the studs, no issues there. There was nothing wrong with the gasket, but since I had a new one, I put it on. I've reassembled 90% of the engine and should be ready to refire today. I need to change the oil and do a few other maintenance items.
2000 KTM 300 EXC (two stroke heaven)
1999 Honda 400EX
Bored to a 406
Lonestar carrier
CRF450 timing chain
1994 Suzuki 250F
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