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top end rebuild help!

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im rebuilding the top end in my kx 125. do i need to rebuild the bottom end if the piston has craters in the top and a little tiny piece of the ear gone? and after pulling the piston out what wud you recommend doing to the jug? would it be worth the money to bore it out any?

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you only need to rebuild or replace a rankshaft if the berings are shot (up and down movemnt) But if the cylinder has scores, gouges, get it replated. Get a new weisco piston kit.i woulnt bore it out just replated.

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if you have piston/ring pieces that are unaccounted for, try flushing out the cases with premix. if there are any pieces in the bottom end you will find out the first time u start the engine.

replate the cylinder

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if you have piston/ring pieces that are unaccounted for, try flushing out the cases with premix. if there are any pieces in the bottom end you will find out the first time u start the engine.

replate the cylinder

How would you go about flushing out the crankase with premix?

Im pretty much in the same situation as this guy.

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How would you go about flushing out the crankase with premix?

Im pretty much in the same situation as this guy.

I did it by pulling the bottom end from the bike, putting it on sawhorses so it was upside down, put a large oil catch below it. Took a big squirt bottle, squeeze kind with a thin exit, filled with gas/mix shoved it into the bottom end and sprayed, while I sprayed my pop cranked the rod slowly. Repeat a bunch of times... then I flipped it over, dumped gas/mix in there, gave the crank a couple turns, shook it around and dumped it out, repeat... then flipped it back over again and kept repeating the process for quite a while. My circlip, the one that destroyed my cylinder, came out and a bunch of flakes... good luck.

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Where did you put the squirt bottle on the bottom end on the underside?? and then when you flipped it back over where did you spray then? when the circlip came out where did it come out of?

thanks for all the help so far!

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Where did you put the squirt bottle on the bottom end on the underside?? and then when you flipped it back over where did you spray then? when the circlip came out where did it come out of?

thanks for all the help so far!

Dad has more tools than anyone I've seen... he had one. Think it came from his job, machinist if that helps find one... might be able to get one from a auto parts store? It was like this but the bottle's squirt part started at the bottom:

480ml-squeeze-bottle.gif

When it was right side up we just filled it with gas. Didn't spray... though you probably could.

Clip came out of the crank area, on one of the turns. We didn't notice it till after the bottle was done for that session.

Some picts of my damage:

n641627882_1482989_7202.jpg

n641627882_1482990_8379.jpg

n641627882_1482988_6751.jpg

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i ment where di you spray on the bottom? wherewas the opening for you to spray into

When you rotate the crank there are some holes that open up, there are also some port holes to the sides if I remember correctly... spray right where the jug mounts to the bottom, right up the rod... this isn't a KX or KDX I think but about the same and the place you should hit:

IMG_2068.JPG

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okay thanks. i think there is an oil drain plug on the bottom? can i use that to spray into? and what fluid are you using to flush the engine?

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OUCH, from the looks of that piston and cylinder, I'd split the cases and check everything as well as replace the main bearings. There is definately some metal floating around.

As for the cylinder, it looks like it will need bored, if they aren't more than .080 deep. Otherwise, you'll have to either get it resleeved or find another one on ebay or something. A machine shop will need to tell you if it will clear. But most likely they won't be able to plate. So if it can be bored, send it to a reputable place, Millenium technologies, LA sleeve, US chrome.

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okay thanks. i think there is an oil drain plug on the bottom? can i use that to spray into? and what fluid are you using to flush the engine?

The oil is for the tranny not for the piston/rod/etc... different oils, different area, so spraying in there won't do a thing to flush out the bottom end unless you have something in that area.

I was using gas mixed 32:1 w/ Yamalube, what I ride with.

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OUCH, from the looks of that piston and cylinder, I'd split the cases and check everything as well as replace the main bearings. There is definately some metal floating around.

As for the cylinder, it looks like it will need bored, if they aren't more than .080 deep. Otherwise, you'll have to either get it resleeved or find another one on ebay or something. A machine shop will need to tell you if it will clear. But most likely they won't be able to plate. So if it can be bored, send it to a reputable place, Millenium technologies, LA sleeve, US chrome.

Flushed really well and been riding it with a cylinder I got from ebay for $50, new rings, and orig piston cleaned up (that was a wesco I got for $50 on ebay) for a while now. Working great and no issues (knock on wood). The cost to get the bottom end done, bearings, replated, piston, rings, seals, etc... I could just buy another KDX in the same condition this one was in when I got it ($550), which if anything does happen I'll be doing. And if it does in the end I'll have a good parts bike and a really good KDX ha... (my ride needs a new frame at some point so...)

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so where do i spray into the bottom of the engine case to flush out the bottom end? i know to spray down the crankwhen it is right side up but where do i spray when it is upside down?

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so where do i spray into the bottom of the engine case to flush out the bottom end? i know to spray down the crankwhen it is right side up but where do i spray when it is upside down?

Same place, spray upwards into the same spot, that way it all runs out (put something below that to catch the spill). Why we used one that had the needle end at the bottom instead of the top.

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Can you catch the gas thats coming out and reuse it to keep flushing?? if not how many times did you do this and how much gas did you use?

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Can you catch the gas thats coming out and reuse it to keep flushing?? if not how many times did you do this and how much gas did you use?

You could but I didn't and wouldn't unless it's filtered... there was quite a few of flecks and junk that came out that I wouldn't want to put back in. Instead of going though that hassle I just used all fresh. We did it about 6-8 times upside down and maybe 3-4 right side up, enough that when we looked there was nothing coming out anymore. We used maybe 5 gals? I can't remember exactly.

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okay thanks man.. and what exactly signalled you to know that you need to flush the engine out? i aint got any damge like that on the jug just some craters on the piston and little piece missing

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I would flush yours out too:prof: Where do you think all the little peices went that was on top of your piston?

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okay thanks man.. and what exactly signalled you to know that you need to flush the engine out? i aint got any damge like that on the jug just some craters on the piston and little piece missing

Clip came loose in the jug/piston and ripped it up. Even if you have a little piece missing your going to have to flush it to get it out. Just keep flushing until your satisfied that it's clean, $10 of gas is better than $300+ bottom end.

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