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Bought a 2001 CR125 Today With Issues...


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Hello all.

Long time listener, first time caller.

I just bought what looks like a really nice CR125 but it does have issues. I think I am going to rebuild the motor but I need a little bit of help on where to begin. I only bought the bike for $375 so I think I did pretty good?

Ok. The problem is that the bike don't kick. Its like the piston is seized or something is stuck. I've tried to roll start it and the back wheel don't budge. The bike moves fine in neutral so I don't think its transmission related. The kid I bought it from said he drove it down the street and it stopped...didn't make any funny noise...then went back to kick it and it was stuck. When I put the bike in gear and hold the clutch it still won't budge. I did notice that the left side radiator is dented on the left side of it, about an inch inward and the shroud is missing.

So with that said, I am thinking the piston is seized to the cylinder.

Would you guys agree? Where is a good starting point?

Thanks!

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I would agree... Take it apart and check.Won't hurt.

Thanks. Do you recommend any of those old tricks of putting certain stuff into the spark plug hole to try to free the piston?

Also, I am fairly new to tearing into a bike. Taking off the cylinder is pretty simple right? Those bolts around the cylinder and then it should slide off fairly easily...if it is not seized??

Thanks again.

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Yep sounds like a siezed engine to me. Do yourself a favor and replace the bottom end too, or at the very least make sure it is at least 75%, otherwise, at least with my luck, the bottom end will go out smoking your new top.

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Yep sounds like a siezed engine to me. Do yourself a favor and replace the bottom end too, or at the very least make sure it is at least 75%, otherwise, at least with my luck, the bottom end will go out smoking your new top.

Thanks. Is it possible to free the piston and not replace anything, or am I going to have to replace the piston and cylinder?

I'm not racing, more just playing...so I'm not concerned about making it screaming fast. More concerned about just making it work acceptably.

Thanks again. You guys are really fast!

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Thanks. Do you recommend any of those old tricks of putting certain stuff into the spark plug hole to try to free the piston?

Also, I am fairly new to tearing into a bike. Taking off the cylinder is pretty simple right? Those bolts around the cylinder and then it should slide off fairly easily...if it is not seized??

Thanks again.

That, i don't know! I haven't actually taken apart an engine too, but from following different threads, and reading ALOT on here, i've learned quite a bit, and heard of many cases similar to this. Dis assembly is easy, re assembly is the hard part:moon:

Two strokes are fairly easy to take apart, from what I hear. Nothin much to em unlike the 4 strokes.

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i think you need someone with some kind of experience with some kind of engine to at least guide you a little. a guy showed me a kx 125 a while back he had bought, the big end was completly loose and rough but he was none the wiser. he was going to do the top end.... total disaster. it does sound like piston siesure cos the crank would likly make noise. you would be surprised what you can get away with if you know something about engines.

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Ok...I let it soak with some Marvel Mystery Oil and then took the head off. I gave the piston a few light whacks with a wood dowl and a hammer and the piston unfroze right away. Didn't put up any fits.

Now....let me show you guys these photos. The cylinder wall looks clean. There is some weird stuff going on with the head and the top of the piston. Any idea whats going on? I imagine its not good ­čśĆ

1.jpg

2.jpg

Thanks again for all your guys help.

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my first move would be, remove flywheel cover, check for vertical play in main crank bearings, remove cylinder and check that big end bearing have no vertical movement. both bearings must be smooth although a tiny amount of play will be ok since its a small budjet build but keep an eye on it. if the cylinder is good fine but worn rings will wreck the motor if they break so get rings, dont worry about dents in the piston crown or the head. its all a gamble but youl learn something. use generous oil mix.....

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Yeah I would agree, the head shows the damage. I would replace it if it was me, I've been through that song and dance before. Trying to get away with something, comes backo bite you in the a.. however my heads are usually much worse looking.

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That head might be able to be re-machined instead of just replacing it and may be cheaper too, but those indentations kinda look like dents from needle rollers that have come out of a bearing. Pull the piston and see what you find.

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That head might be able to be re-machined instead of just replacing it and may be cheaper too, but those indentations kinda look like dents from needle rollers that have come out of a bearing. Pull the piston and see what you find.

Thank you everybody for your help.

I agree with you. The dents look like somebody took a flat screw driver and hit it.

I think I'm just going to try to run it as-is and pray for the best.

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every time you kick it, your probably doing more damage, there's loose metal that caused the damage you see on the head/piston, and it'll be down in the crank

hope the cylinder is still ok, those are expensive

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every time you kick it, your probably doing more damage, there's loose metal that caused the damage you see on the head/piston, and it'll be down in the crank

hope the cylinder is still ok, those are expensive

Can I not flush that out?

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