KDX250 seized, can't remove cylinder from crankcase

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mud99
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KDX250 seized, can't remove cylinder from crankcase

Post by mud99 »

So I lent my 1991 KDX250 to a buddy, and he seized it! It looks like it ran out of coolant and overheated.

Anyway, I'm trying to take the top end off to assess the damage, but I can't separate the cylinder from the crankcase. The 4 crankcase nuts are off, and the power valve lever has been removed from the bushing, but the right hand side of the case won't move.

I've hammered on it with a rubber mallet extensively, but it doesn't budge.

I think the dowel pins might be frozen due to age and corrosion - this bike is still on the original top end from 21 years ago!

What should I do?
KarlP
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Re: KDX250 seized, can't remove cylinder from crankcase

Post by KarlP »

Everybody needs buddies like that....

You are probably right about the dowels. I guess the next step is a hard wooden block or dowell and a regular hammer. Knock it up, left, right, it's got to come off.
'08 KTM200xc
'99 CR/KDX Hybrid with that RB stuff done to it
KX100 for the boy
pumpguy
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KDX250 seized, can't remove cylinder from crankcase

Post by pumpguy »

Have you removed the head? What does the cylinder bore look like? The answers to these questions will determine the next course of action.

With the head off, you might try rigging up a puller using a metal bar with holes drilled to match the head studs. If only 2, the holes should be 180 degrees apart. Then drill and tap screw threads in the center, between these 2 holes. 1/2-20 would be a good thread size but anything substantial would work. Now install a long bolt into this threaded hole.

When you tighten this bolt against the piston, this will cause a pushing force against the piston, and a lifting force on the cylinder. I would use a metal cushion piece between the bolt end and piston crown. Careful tapping the cylinder with a metal hammer will also help. You don't want to damage the cylinder unless it's beyond repair.

Depending on where it is seized, you could also try to rotate the crankshaft with a socket on the flywheel nut.

Just some ideas based on information supplied.

Good luck.
mud99
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KDX250 seized, can't remove cylinder from crankcase

Post by mud99 »

Ok, so here's a bit more information - it is locking up when I try and rotate it past BDC. The cylinder and piston and head all look OK and move freely

I can get it to wiggle a little bit, but it's like their is another bolt holding it together or something.

Can someone confirm that removing the 4 cylinder bolts is all I need to do to? Is their a mystery bolt somewhere?
zepplin153
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Re: KDX250 seized, can't remove cylinder from crankcase

Post by zepplin153 »

you're probably missing something. I am not familiar with your bike (I have rebuilt a 98kdx200) but I looked at some engine pics and parts diagram and there looks like there is a similar pin involved with the actuator shaft on your bike. its held in place with a small screw on the right side. Behind the screw is a little pin. It can be a b*tch to get the pin out sometimes and easy other times. But please don't resort to using force... Yet. I have worked around engines for a great while and have learned if it doesn't give your forgetting a nut, bolt or screw. I worked on 2-stroke outboards for a long time too and have seen the worst in the way of corrosion and have never seen a pin prevent removing something. Keep looking you will find it, and you will probably want to kick yourself when you do.
'98 KDX 200 (KLX300 Forks)
mud99
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KDX250 seized, can't remove cylinder from crankcase

Post by mud99 »

Ok I got the top end off, I wrapped a ratchet tie down around the exhaust, hooked it to the handlebars, cranked it until it was under a lot of pressure, and then whacked the engine with a rubber mallet and it popped off.

Cylinder and piston are in great shape, but the main bearing and big end rod bearings are both very stiff and barely move.

I guess I need to split the cases to figure out if things are damaged?
pumpguy
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KDX250 seized, can't remove cylinder from crankcase

Post by pumpguy »

I would think it's the lower end rod bearing that seized. Is it free to rock front to back? If yes, it's something else.
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