2010 Yz450f cylinder/piston scarring after blown headgasket

Recently my 10 450f started pissing coolant out of the overflow under heavy acceleration. We decided it must be a blown headgasket.

After tearing it down we noticed some pretty bad scarring on the piston and a little in the cylinder too.

What do you guys think could have caused this? I had just put a high flow water pump and new mishimoto radiators to resolve an overheating issue.

I guess it's big bored time, any kits you guys recommend? Any supporting mods recommended?

Thanks in advance for any info, Adam




Edited by MiranAdam16

That looks like classic piston seizure, in this case most likely as a result of the overheating condition causing a clearance problem or an oil failure.  


If you're going big bore, have the crank balanced for the new piston.  Use a two compression ring piston for best longevity. 

Do you think the cylinder is worth using again with a stock replacement piston?

Edited by MiranAdam16

Doesn't look like it.  But, if you can hone it clear of any scoring/marks and then measure it to be worn less than .002" anywhere, it could be. 

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