Yz450 head damage

Can anyone tell me what would cause this damage?

Engine was rebuilt to new spec 6 hrs ago. Bike ran awesome.

Oil was changed after each hour of riding. I'm just trying to learn how

to prevent this scoring of head.

Thanks in advance for advice!

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This happens when the area receives little or no oil flow .This Usually happens after a rebuild where the oil takes a while to circulate and no or very little assembly oil was used!!

Thank you

what was the reason for the rebuild in the first place?

if deffanitly wasent getting oil up there. possible a pump failure or some thing is blocking the oil passage going up to the head

Thanks Dave .

It was a complete build as the con rod broke and smashed everything.

New cases, crank , rod and piston, rebuilt head,

New cylinder .

Did you use OEM gaskets?

No , aftermarket gaskets.

Thanks for all the replies.

I had almost the exact problem, i think it was the base gasket. I used a cheap aftermarket gasket and OEM is metal.

Thanks very much

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