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Whats happened to these 07 CR250 heads?

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Hey guys have a look at these 2 CR250 heads.

They are off an 07 that im rebuilding for a mate.

His bike is bog stock...mikuni carb, stock cylinder and head, pipe, jetting......everything.

Im giving his bike the exact same makeover as my 07...... Keihin PWK, 030 base shave, head recut and squish set to 050, vforce 3 reed block, FMF fatty pipe etc, etc. ...its gunna be a good makeover!

So, when i send his head off for machining, we hit a hurdle......the machinist has uncovered a heap of "corrosion" on the edge of the combustion chamber and the head is past cutting.......

No problems says my mate, ive got another head at home that was on the bike, we can use that'

Surprise surprise, this head has even worse damage, in the exact same spot!!

Have a look and let me know what u guys think, is the detonation and excessive squish the cause of this? Or is it something else? Coolant burning through the head gasket?

A bit of history on this 07; .......his uncle has worked on the bike previously and the head gasket was on backwards and the RC valve was installed upside down, meaning that the flap could never fully open and uncover the exhaust port!!

Opinions and theories are all welcome.....cheers guys

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Looks like a leaking head gasket to me. Especially when you say that his "uncle" installed the previous one backwards as well as incorrectly installing the RC valve cover. I would check the cylinder to make sure that there are no cracks in it and then assemble the engine per the manual.

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I would say it was caused by detonation. Just because this current piston has no signs of it, doesn't mean another previous one didn't. We all know how prone the last CR's were for detonation. It would've only taken one hot slow trail ride with lousy fuel to overheat the head to the point where it started to erode.. That's just my thought, and could be wrong. You could also check the deck of the jug to make sure it doesn't have a low spot to cause a coolant leak, because that too would cause the erosion.

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thanks for all the suggestions so far.....i'll post up a couple more pics tonight.

 

im leaning towards a loose stud, mainly due to the deformation of the old head gasket around 2 of the studs, like they werent screwed down far enough?.................

 

I didnt get to remove the head and cylinder, the "uncle" pulled it down for him.................the plot thickens

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