Complete Top End Rebuild?

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Feb 16, 2003
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#1
Hey All,

I just wanted to ask everyone a question regarding the top-end of my bike. I have a 1999 KX100 that as far as I can tell has never had a complete top-end rebuild (piston and everything) much less a ring job. I am at least doing a ring job but would like to save some money so I am wondering if I could get away with just doing a ring-job. Any comments or advice would be greatly appreciated. The bike doesn't look to have too many hours on it which is why I'm asking this question. Thanks in advance. --dirtfreak
 

gwcrim

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#2
Until you take it apart, it's hard to tell what it needs.

If the cylinder is a just a bit worn or only has some very small scratches, new rings ought to pep it up a bit. Keep in mind that the Kawasaki cylinder plating isn't the most durable. If the piston is scored or burnt, you'll absolutely want a new one.

Have someone measure the cylinder for out of round, etc. and see what it looks like. A visual is the only way to tell what you need.
 
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#3
gwcrim,

First, thanks for a quick reply back. That's what my dad and I were planning on doing is taking a look at what the piston and bore looked like and going from there. A new piston kit from Wiseco runs $57.99, and additional costs for the wristpin bearing and gaskets brings the complete job up to around $91. That's not too bad, but like I said I am trying to save money for a truck and insurance and that's why I thought I'd ask. Thanks again, and any further comments are appreciated.
 

Rcannon

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#4
It sounds like you might have bought the bike used. If so, I would replace the piston. You never know how the previous person took care of things.

I bought a used YZ 250 and had no idea of what was going on with it. I rode it one day and decided to check out the top end much like your doing. I found a slight crack in the piston. I was lucky to catch it before it caused really serious problems.
 
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#5
dirtfreak,

I have to agree with Rcannon. If your bike is used, who knows how the previous owner cared for it. Especially if he was loosing interest in the bike, I'm sure he lost interest in maintaining it too.

I also bought a used bike, an RM-250. The bike was dirty, and the air filter was even dirtier. I took the pipe off and inspected the cylinder. Using a flashlight I observed the piston while cranking the motor. It's alot easier if you remove the plug. My piston was very scored. I reached in with my fingers and could physically move the piston in the bore. When I took apart the top end, I found the plateing was totallly gone around the exhaust port.

I posted the same question as you are, and was dircted to:
http://www.ericgorr.com/

I contacted Eric Gorr at Forward Motion. It's best to call early in the morning. He even answers his own phone. He can give you good advice. I wanted my bike to be mechanically sound, but wasn't going to race it. I didn't need the super polish and port job. He saved me some money by swaping my head for a servicable one. (within factory specs) He sent the cylinder/piston/gasket kit for around $200 after crediting me for my cylinder. He also suggested installing a new wrist pin bearing, which I did.

He's a good guy and a supported vender. Give him a call and see what he thinks. If your gonna keep the bike for awhile, you might as well make it right.

Good luck, Steve.
 
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#6
Thanks everybody for your advice. I think I'll wait and take a look at my piston and bore before making a final decision, but right now I'm definitely leaning toward completely rebuilding; especially after hearing your experiences! Thanks again for all your insight and comments. --dirtfreak
 

Rcannon

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#7
Dont worry so much about it! Look around at some of the mail order places. Rocky Mointain ATV sells a weisco piston for your bike. The cost is hardly worth the labor to take it apart again. I replace mine while I am in there.
 
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#8
Hey guys, I have a (89 I think) Cagiva WMX 250 2 stroke. I recently purchased it and after some engine troubles which i put down to a fowled plug mainly but a black clogged up air filter and dirty carb jets did not help.

So the new jets are on their way, carb has been cleaned et cetera.

So I though i would look at the engine.

The piston crown was completly black no metal to be seen which i cleaned up a bit but still black.

The cyliner does not hae any deep scratches but where it is scratched its a different colour like the cyliner has been plated and in places worn down, but there dont appear to be enoguh damage but im not to sure.

Also i can move my piston from side to side a very little amount.

I am thinking about rebuilding it as it dont look in good condition does it sound like it needs it?

Also there is two nuts inside the cylinder (in the watercooling part) one of which is undone and the other nuts that hold the cylinder on have been undone.

But sockets keep slipping on the but as its rounded what can i do as i can get stillsons on it as its right inside.

Also i was thinking of stripping it and putting it into a shop to replace the piston and torgue up is this a good idea as i cant afford for there labour charges.