kx250_engine

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Engine Strip & examination
Kawasaki KX 250 (1991)

A neighbour has asked me to check his old KX. I was rattling badly (and he thought from the bid end), So I stripped the top end in the frame at his place.
I found very damage to bore, a little piston damage (not serious) but when it somes to the big end, well it's seized, not solid, but too stiff to run.
The engine is a water cooled single, two stroke.
I've done a bit of reasearch on the net and found a micro fisch of the bike, as I don't have a manual available for this machine at the moment, I'm having to reverse engineer the engine to get the torque settings. You just set your torque wrench on a light setting and increase the setting by 1ft-Lb Or 0.5KG-newtons) until the nuts release, just before the torque wrench cracks.
Then take an averadge (unless you see threadlock has been applied previosly if you are a mechanic, you'll understand that) to get setting for rebuild.
Si

The head was removed in frame,
Only a couple of small chips in the head, servacable.

Barrel movement was checked using the kickstart lever watching the piston. it seemed too stiff, ( like it was under compression, but with no head????) Big end of seized main bearings? This is why I decided to remove the barrels (still in frame)

I also checked the top of the pistons befor I removed the barrels I chesced the sides for signs of scoring after barrels were renoved

Twisting the con rod let me know it was big end related.
This is we knew it waas going to be a crank case split, so the engine came out, and now sits on the bench

I had to clean the engine twice before I went further, once to rmove the dirt from it's last use, then degrease her as I remove parts. To re build an engine it it has to be spotless, grit kills bearings.

As the damage seemed to be heat related, I decided to check the cooler impeller for damage, this one looks good, no damage.

Removal of the clutch casings,

Using a small piece of wood and a hammer so gently tapping the casing free, nice and eavenly, there are three places designed for the job on the middle casing.
I've noticed the thickness of the paper gaskets, so making new ones for this machine won't be hard, same as I did for the RX

Middle casing shows the clutch and gear lever arrangement internal, I'll try to leave the clutch as is if possable....The basket itself is showing of wear from the first three plates, and it seems to have been in contact from a gear at some stage. It doesn't need replacing though, just need to check all bearings properly.

I believe I can just remove a circlip and two cogs from the crank on the right hand side of the engine just in front of the clutch (this we'll see when the crank cases get split)

Next we come to the generator casing on the left side of the engine,

when the casing has been removed, I check the wires to the pick up before removing it, this is as far I've got so far I've tried penatrating oil to help loosen there screws, an impact driver has been tried.Still no good.
I'm missing my old dremmel too, I need to cut a groove to get these out. I'll replace with new.

and see what puller I'll need to remove the rotor from the crank (it has an internal thread, so I know what sort of puller I need) Might bet one of my external pullers to do the job, I'll see. Loosening this nut can be a problem too, you have to stop the crank from turning by....

placing a suitable bar through the small end of the con rod, and place a ciece of wood under the bar and over the crank cases to stop any damage. If the wood starts to give, place another over the wood and below the bar.
I managed to get this one done with the latter method without damaging the con rod, even we had a new one on order.

Then undo with a good crack bar in the normal manor.
Note it's easier to undo this nut in frame if you know it has to be removed. Otherwise you''ll beed an angine vice on your workbench or someone else to keep the engine still, I held it while the owner got this one, (new engine vice will on my new bench)

Then we come to the rotor itself. I don't have the reccommended puller, but I modified my 4" three legged puller to fit. Note if you use this method, only let three mm of the leg into the rotor, that's where it will only meet metal, any further than that and you might damage the magnets This one came off with no prblems

with the rotor removed you can see the magnets inside the rotor as well the Wood ruff key in the crank, it's that key whick make the rotor spin. You can just see the groove in the centre.

Next came off the Stator plate, the plate was marked before I removed it, so I know exactly where it came from, don't want to adjust the timing. I didn't have to remove the pick up box, so that was left in situe

After I removed the stator plate I found all this gunk. I de greased this and cleared the little oil/petrol way which is supposed to give it some lubrication. it seems to be ok the lack of lubrication here, maybe we caught it in time

I removed all the crank bolts, and removed the clutch plates, I was unabled to remove either using the tools I have here (my clutch splitter worked on my RX, but not on this engine, it will do the job for the rebuild though)
So I got the engineer to split the crank cases and split the clutch before he Re built the crank for us.
Unlike my RX crank which uses shell, this ones uses roller bearings and the crank splits into 5 pieces. getting the srank in aleignment is a job I've never done, and knowing my limetations, I got that dome properly, thanks to Jim Axford (on my Oxfordshire dealers/accesseries etc page) now Paynes no longer have a bike engineer working for them, they reccommended jim, and I'm happy with the results.

Here the rebuilt crank with new con rod/big end journal/roller bearing and washers fitted, the mains bairings were full of ground up roller bearing from the damaged big end roller bearing, but after flushing through with de greaser, they were found to be servacable.

Now we come to the damage and what caused the big end failier....Lack of lubrication!
As this modle has no oil to mix the petroil mix it can't be a blocked oilway or pump failier, so it must be dut to lack of oil in the mix in the tank.
I asked the owner before the strip and he assured me he put enough in. Turns out he hadn't. He knows now.

If you want to see the rebuild
CLICK HERE