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What do you think has caused this damage ?? Is it safe or practical to run it as is ?? BTW Its a YZ80 head. Any help appreciated.

Looks like a leaky head gasket. Water damage.

I wouldn't run it like that. Time for a new head and gaskets. What does the piston look like? Might need a whole top end job.

***edit*** BTW why is this in the RB section?

RB is the resident head expert so I figured he'd more likely see it here. I presummed he has seen his fair share of heads and may know the cause.

Piston and cylinder to be measured soon but they both look decent, ie. no visible scores on bore or damage to piston..

You sure that a broken ring or locator pin did not bang around in the chamber for a minute or two? New bike to you? First time you had the head off?

Looks like my old 350 Chevy after pieces of the top rings moved up the sides of the piston (fragmented bits) and strolled from cylinder to cyl. beating the crap out of my piston tops. Left the heads(cast iron) unscathed. KayDee, is that corrosion or mechanical impact? Get out your magnifying glass!!

I have seen this so many times especially with the Yamaha YZ 80's....

It either lost a bottom end or scattered a piston, any or all of this destruction will pepper the top of the piston and head. The pock marks on the head can be cleaned up, but it may be cheaper to buy a new head.

It sounds like the cylinder has been replaced and other damage, but the head was re-used.

Ron

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Thanks Ron exactly the info I was after. It one of my mates little bikes and it's got bugger all compression so I've pulled it down to suss it out. Cheers all... Trev...

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GS wrote:Looks like my old 350 Chevy after pieces of the top rings moved up the sides of the piston (fragmented bits) and strolled from cylinder to cyl. beating the crap out of my piston tops. Left the heads(cast iron) unscathed. KayDee, is that corrosion or mechanical impact? Get out your magnifying glass!!

Well to me it looks more like some weird kind of corrosion but what do I know.

I tried to get some clearer pics.

Looks mechanical to my squinty eyes, perhaps occurring some time ago. Probably not a potential point-of-failure defect, but whether to replace or not would depend(for ME anyway) on the reasonable availability of another serviceable part.
Let us know if more info comes to light
Greg

That damage appears to be by running extremely lean. It is melted aluminum.

I agree with RBD. Something came apart and rattled around in the combustion chamber before the engine was stopped. Who ever owned the bike R&R the damage and reused the head.

When you melt a piston there is a hole in the piston and a few flakes of aluminum in the exhaust tract and lower end.

HOw can a bike run with a top end like that??????

Anyway... it's funked up. Replace it you cheap bastage!

interesting how I get a "party poker" pop-up after looking at those pics. Maybe they'll pay you Ad money and you can buy a new head?

Colorado Mike wrote:interesting how I get a "party poker" pop-up after looking at those pics. Maybe they'll pay you Ad money and you can buy a new head?

Uhoh your on to me !!

It is going to be replaced but it would also be good to know what caused the damage in the first place. The piston has a few small marks and the bore is good. I'll post pics of the piston and see what you guys think.

Cheers,
Trev...

OK since I got busted with my Poker scam you will have to click the link to see the pics.

CROSS HATCHING EVIDENT
http://img135.imageshack.us/img135/9382/img3017hz0.jpg
CROSS HATCHING EVIDENT AGAIN (bit blurry)
http://img80.imageshack.us/img80/6480/img3018vn7.jpg
PISTON DAMAGE
http://img80.imageshack.us/img80/9972/img3020hu5.jpg
PISTON DAMAGE (closer)
http://img227.imageshack.us/img227/1852/img3021ez5.jpg

Something hard, beatin up that soft aluminum. Top ring still there? Insufficient end gap will produce similar results. (Now, how did I know that?)

It only has one ring and yup its there. Some slight signs of blow-by.