2007 YZ450 Coolant leaking through overflow. Blown head gasket?

6 replies to this topic
  • yamaman1

Posted January 28, 2013 - 08:19 PM


2 rides ago I noticed my coolant was low so I filled it up thinking it had just boiled over a little. Last ride I had a pretty constant drip of coolant coming from the overflow within 1 mintue of the engine being on, iding or riding makes no difference. Thought the rad cap was bad so I swapped it with my buddies which works fine and same problem. Today I started the bike cold with the rad cap off and there are small bubbles coming up through the coolant. Im assuming the head gasket is blown and possibly a warped head. Ill know more when I tear into it but is there any possibility the cylinder is warped as well? I dont really know what would have caused it or what else to look for, I have just over 80hrs on the motor since I split the cases to fix 3rd gear, and everything looked good and I put all new gaskets. Anyone else have experience with this? Thanks

  • yamahakid88

Posted January 29, 2013 - 07:46 AM


Sounds like a head gasket to me, but you have to figure out why it blew a head gasket

  • hillclimb426

Posted January 29, 2013 - 09:04 AM


Use Oem gaskets. Had this happen on a rebuild using aftermarket gaskets 2 times. Had the head and cyclinder checked at machine shop. Everything was in fine. Ordered Oem gaskets put bike together and she runs great. No head gasket leak.

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  • yamaman1

Posted January 29, 2013 - 05:46 PM


Just open up the motor and surprised that the valves still are in spec, with almost 200hrs on the motor. I havent had a chance to get the head to a machine shop but there is no doubt coolant was all over the head gasket.

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  • yamaman1

Posted January 29, 2013 - 09:32 PM


Took the cylinder off and the base gasket had coolant on it too. I think when I put everything back together previously I torqued the head down wrong and I also noticed that there are a couple rough edges on the engine cases and cylinder, there very small, just enough to catch my finger nail. it should be ok the just clean up those edges with some fine sandpaper? I'll be replacing the piston and cam chain. How does my cylinder look? The only thing noticable it some disoloration at the top edge right and left side.

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  • yamaman1

Posted February 03, 2013 - 09:25 PM


What do you guys think of the cylinder? Would it be safe to run it as is or does that discoloration indicate too much wear?

  • Do I Care?

Posted February 04, 2013 - 06:07 AM


I would be giving that barrel a rehone. I looks a bit glazed up. Other than that it looks fine.
Make sure you have the timing right when you put it back together as this is the most likely cause of blown head gasket. It also overheats,runs like a 250,hard starting,lean,backfires when acceleration is let off ect

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