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KX125 Big End seizure

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Hi there - have a KX125 which, from the frame number dates from 1990. Whilst riding it over the weekend the bike seized. Have taken head and barrel off and found fragments of metal in the inlet port which I am guessing are from the big end bearing (duh, I was running it on around 50:1 and now realise it should have been around 30:1!).

A couple of questions for those far wiser than me!

  1. How do I remove the rear swing arm pivot, which is the final obstacle to removing the motor? The bolt was only finger tight on the left side, but am not sure how to remove pivot bolt - does this simply require drifting out, once I have removed rear brake pedal (workshop manual is on its way, but will not arrive for several days!)
  2. Is a complete new bottom end kit still available for this model (preferably in the UK, but if not, from the US)?
  3. Aside from a puller, are there any special tools required to complete the strip down and replacement of the entire bottom end?

I appreciate that given the age of the bike, the replacement of the entire bottom end might not be capable of being economically justified, but I am keen to do this, if only to broaden my experience of two stroke motors!



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I'll answer 1 and 2.......

1. I have found Kawasakis to be very common for seized pivot bolts. maybe it's just my bad luck but nearly every one or every second one I do is seized.

if u can't smack it out with a drift. remove subframe. remove shock. get as much out of the way as u can.

you need to cut through the pivot bolt between engine and swingarm on both sides.

quickest and easiest with a very fine cutting disc on an angle grinder if u can get it in there without damaging anything

option 2.... few hours with an air hacksaw

once your through. remove engine and smack the rest out.

you will need new swingarm bearing kit and pivot bolt

2. you may need a case splitter. kx's can be tight trying to get apart

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Thumbs up, Man. You're doing good on you own so far. Looks like you're on the right path. Good job researching and getting a manual.

The only thing about running 50:1, that must only be done with a top line synthetic oil. Any type of Dino oil...32:1. But it's not uncommon for the Big end bearing to sieze. That's what is the main culprit in needing a crank. Mains are rarley the issue.

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