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Can you explain this burn pattern???

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This is the piston from my son's KX100, the bike was running fine just down on power and the compression was at 110psi. The dome has pits all in it from a previous top end coming apart I guess. Looks like some took a dremel to the dome to smooth things out. Is this what's causing the funny burn pattern??

http://gallery.me.com/markgable#100009/IMG_0495

http://gallery.me.com/markgable#100009/IMG_0499

Can I fix the dome somehow, or just buy a new one?

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your head looks fine with the exception of the tool marks. your piston..... i've never seen a burn pattern like that before. the only thing i can come up with is that possibly its getting extremely hot there and causing the fuel to carbon up before it gets a chance to explode. but that's a guess. I really don't know. sorry brother.

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your head looks fine with the exception of the tool marks. your piston..... i've never seen a burn pattern like that before. the only thing i can come up with is that possibly its getting extremely hot there and causing the fuel to carbon up before it gets a chance to explode. but that's a guess. I really don't know. sorry brother.

That head looks fine to you!?

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Your squish is not right. Most bikes come this way and you can have a machine shop get it right.

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That head has been damaged by debris (broken piston parts, wrist pin circlip, bearing parts, etc.).

What let loose previously?

Very odd wash / burn pattern, it also looks like uneven port flow..................

That plug looks awfully lean at idle too.

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The piston looks like unbalanced transfer flow, not really all that unusual.

The head definitely shows signs of eating something metal at some point in that bike's life.

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Bizare burn pattern. Is that piston cracked underneath? Does the bottom have the same pattern or is it an even chocolate brown pattern underneath? I have never seen a pattern like that. The head has taken some hits.

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The piston did not have a mark on it anywhere except the top like you see. Otherwise it looked litterally brand new. The cylinder looked great.

We bought the bike used a couple of months ago. Supposedly it had a topend done and had about two hours on it. They didn't tell me about it breaking a ring and chewing up the head, but obviously that's what happened. I'm hoping the cylinder has not been bored or honed out of spec as I just ordered a new top end kit (OEM spec). I noticed the intakes had some severe casting flaws, one so bad it actually had a piece of aluminum about the size of a piece of rice about to chip off. I smoothed out these flaws with a dremel (very carefully) and polished everything up. I have no idea what the jetting is going to do now that the airflow will change. I'm looking for a new head on the auction sites.

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The head is not causing the funny burn pattern, that would be the transfer ports causing that. The dings in the head look to me like it lost a lower rod bearing at one time before you got the bike.

Ed

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It does have a hot rods connecting rod in it, so I suppose you are right Ed, it must have lost the rod bearing and they replaced everything with the aftermarket stuff. I noticed that the connecting rod had about 1/8th inch tilt or play side to side in it, no vertical play at all. From what I read here, it seems that's not too big of a worry, so long as it has no vertical movement. If I decide to replace the cylinder sleeve, does that have to be pressed in and out or can that removed and replaced easily?

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It should be plated, if it is sleeved they must have done that to in the rebuild. We don't change sleeves our self but if it is sleeved you may be able to get it bored and put in a bigger piston.

If its plated and needs it you can get it replated and then use stock pistons. BTW the HotRod crank is good stuff. You check side play and up and down play, if no up and down play and it is smooth you are probably fine. I am guessing the blew it up, rebuilt it and sold it. Good luck

Ed

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it's a 2002 KX100, I was reading somewhere that prior to '03 that it has a Nickasil sleeve?? Maybe not....I wouldn't know the difference!

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it's a 2002 KX100, I was reading somewhere that prior to '03 that it has a Nickasil sleeve?? Maybe not....I wouldn't know the difference!
All models of the KX100 use electrofusion cylinder coatings. Only the 125 and 250 got nicasil in '03.

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That head looks fine to you!?

I'm not saying the head doesn't need to be replaced, I'm saying that the scoring from the topend coming apart didn't look like they caused the abnormal burn pattern.

I don't know what would cause that pattern, but I'm learning a lot from this thread.

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The head doesn't look fine but I have smoothed out the sharp spots and used heads like that before. Almost alway caused by a rod bearing going out.

Ed

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Well, we got the top end done tonight and began the break in.... I guess the tell tale sign will be what the compression reads after we get the rings seated. I smoothed out the head and cleaned it up a bit, but did not replate or replace either the cylinder or head so here goes nothing!

I'll update on how things check out. thanks for all the help so far!!

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