Kx 125 please give suggestions

So..... thumpertalk I have some questions I know you guys always here to help. I bought a kx125, barely running with soooo many problem. So you may wonder why I would do so but I intentially did this so when I was done with it it would be done my way if you know what I meen. I was really hoping hoping I didnt have to go into the bottem end but im not sure if I need to or not now. Now I fixed everything going on with it before going into the engine minus the brakes so far. The left radiater was litteraly ripped in half and the other was disfunctional also so when the kid was riding it had no coolant at all. I now know for a fact the the head is worped and most likely the jug, so im going to wait untill christmas for my mom to get them. When I first got it, I took it completly apart, it wasnt blown up but the cylinder sleeve had horrible scoring on it. I decided to put it back together for the hell of it, and to my surprise it ran amazing, with all the old parts, cylinder rings gaskets everything. It was leaking antifreeze out the headbolt because of the reused gaskets but I planned on taking it apart again anyway. So its running great litterly no noise so I think awsome im just going to get the new gaskets and see how long it will last. So I do all that, put it back to gether again and it I take it to the end of my street take it back and it shuts off like I pressed the kill switch. When I take it apart again, the rings were smushed inside the piston and both the circlips fell out somehow. Now I know im doing this right, my dad was overwatching and he is a ase certified master mechanic and also he can fix anything from dirtbikes to a freaken t.v. so I really am trying to avoid splitting a case because ive never done it before, and im starting to lead towards a stretched rod judging by the picture you will see shortly with all those nicks. I never seen it that bad. So im gonna stop rambling now. Any suggestions would be greatly appreciated for this birthday present gone wrong. And when I say barlely running when I got it I meen it sounded absolutely horrible. Again thanks to everybody who took the time to read all this, and im only 16 so I have a hard time getting and holding on to money because im a kid I guess so any help with how to get some possible problems done cheaper would be great. Thanks!


Figured I should also show what the piston looked like upon thr first tear down


First what year is the bike ? Are you sure it sleeved and not a chrome bore ? Never reuse circlips they are one time use usually. We fix cylinders and heads that are warped all the time in our shop. The pits will have no major effects on performance in the head. The bottom end should be split because that is usually where stray parts go. Then you put your new fresh motor together and bam some garbage comes up the transfers and wipes out your new cylinder and piston. Depending on the year and what you payed you may be better off investing in something elsr as you could be looking in the $600 to $ 1000 range. Your mains will need inspected along with the lower rod bearing as it is easy for a circlip to get in there. you can chance just listening to the bearings and feeling for notches in them. The rod should have no up and down play some side to side is fine though. Turn the motor upside down and flush with 2-3 cans of brake cleaner while rotating the crank to flush out debris. That's a crap shoot though. Minimum I would say top end kit $80 to $140 depending on the quality you use. Machining the head $65 to $75, machining thr cylinder $65 to $75 to make it flat again. $60 to $80 on a bore if it is sleeved. $200 to $250 on rechrome if its chrome plated. That would be your bare minimum.

Yes it is sleeved im sure of it and can I have the info to send my parts to your shop. My cylinder needs to decked also. I guess im going to split a bottem end for my first time. I already have so much money into it is the first reason im not backing out. I also wouldnt be able to ljve with myself if I just abanded it. Its a 97

Also is it possible to bore to sleeve and is there a good way to split a case if I dont have acces to a flywheel puller.

Im selling my bmx bike for 250$ if I could ship it to you can you do the machine work for around that price

Yes. But I can not bore the cylinder without having the piston you are going to use.

I would prefer if I could send it to you know how much over to go then get the size piston you recomend because im not sure how much of a bore it needs because im unsure. Once my bmx bike sells I can ship the parts to you immediately along maybe a .6 or .3 over piston or something. I never really got into boring things out and all of that becauese all my bikes are taken care of before anything like that can happen to them. I look forward to aranging this as soon as posible thanks. Your not in driving range of south jersey are you?

No we are in Toledo, Oh and we are the cheapest in the country on namura,, prox, and wiseco. We can definately get you taken care of. We also build some of the fastest motors in the country. When your ready you can call 419-472-8773. Ask for John.

What year bike is it? It looks toasted literally. You might be cheaper to just part it out and start with a running bike. Or keep searching ebay for a complete used engine for it....then sell what ever parts you can salvage from yours to recoupe some money.

Figured I should also show what the piston looked like upon thr first tear down

your dad is a mechanic and he let you put it back together like that? :jawdrop:   :naughty: .

It looks like the front cylinder stud is broken. 

Its not broken there the wrong studs and I wasnt expecting it run good for awhile I was just inspecting the bottom end to make sure it was good

you still have not said what year it is.

He said 97

you still have not said what year it is.

he did , he said its a. 97.

He said 97

:banghead: ...yeah I missed that. too busy looking at the carnage... :cry:

:banghead: ...yeah I missed that. too busy looking at the carnage... :cry:

yea I know, for someone who's dad us a "master mechanic". And he'd let him put that back together and red it? That's dumb, especially that he ordered new gaskets even though it was already ruined..

If it's still the original bore, I'd send the cylinder to Millenium for a replate.  Buy a head off Ebay. New top end, new crank, etc.  You'll have a brand new engine when you're done.  You can go spend $150 on a 2005 KX125 and have it blow up in one ride.  If the rest of the bike is decent, I'd rebuild the engine.  If the chassis is all clapped out then might want to part it.

Edited by Jeekinz

J this kid is right down the street from you...go save this bike.

Post a pic of the cylinder, top and bottom. Than we can tell you if it is sleeved or not. The head needs to be be either machined and rechambered for squish or replaced. You can sand most of those grooves out but you will have hot spots and cause detonation which you don't want on a small bore screamer.

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