YZ400 Head questions

On the YZ400f head on the left side, there is a hole. Is this supposed to be plugged with a soft plug or something? Is it an overflow hole? When I start my 400 I let it run and after running for a bit, coolant starts to come out after I shut it off. Not much but alittle. I just replaced the cylinder and am curious if this is normal due to to much coolant or if it is something I should take a look at. Thanks.

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That is the drain for the spark plug well, which allows water, oil from a leaking cam cover, combustion gas from a loose plug, or whatever, to drain away, and also prevents a build up of air/gas pressure from popping the plug boot off.

Coolant should never come from this hole unless the head is cracked from the water jacket into the hole. How certain are you that it's coolant you see?

Positive. Its greenish fluid. My head is cracked in the water jacket, but I tried to fix it with JB weld. Apparently it is cracked inside the water jacket where I cant see. Looks like I need a new head.

Check ebay, I think there is one on there.

Think that radiator stop leak would work for hairline cracks? Anyone have any info or would that gunk up something? Im looking for a cheaper fix due to the fact that Im a poor college kid.

That hole is also for blowing debris out from around your plug before removal.

Think that radiator stop leak would work for hairline cracks? Anyone have any info or would that gunk up something? Im looking for a cheaper fix due to the fact that Im a poor college kid.

I doubt that it will help. Water jackets on the bike are smaller than the ones on a car, and I cant help but think that that stuff will gunk everything up and cause more problems.

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