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KDX 125 engine failure


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Hi all,

I recently picked up a cheap 1996 KDX 125. I know this wasn't sold in the USA but I hope my question is more general than just for this model.

Anyway, I have only ridden it a few miles but yesterday the engine cut whilst riding and it wouldn't restart. I feared the worst and, sure enough, when I took the exhaust off I could clearly see two huge gouges out of the bore on the side opposite the exhaust port. I started stripping it and got to the last bit, where I tried to lift the barrel off of the piston but it won't come. I think a ring has broken and is now interfering with the inlet port, meaning the piston won't pull out of the bore. This means the barrel is now stuck on the engine and I can't get to the piston. The engine is still in the frame.

It looks like the barrel is junk, and the piston, so I am happy to trash these to get it apart, but would like to save the conrod if I can. Does anyone have any advice on this? I can't get any clear access to the inlet port to try and free it from this side. I can swivel the barrel around the piston (with some resistance) but only about 200° or so as there are a couple of items on the engine that prevent the barrel turning through 360°.

I thought about rigging up some kind of press, using the cylinder head studs and screwing down onto the piston crown to push it out but can't work out yet how to rig this up.

Any other tips, hints or advice?

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Of course, I'm assuming it's a ring that has caused the damage - could be some other foreign object in there I guess? KIPS valve? Doesn't matter really, I need the barrel off to see what's what!

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Assuming you have the head off, pour some oil down onto the piston. I have had some success with this lubricating the cylinder wall and allowing me to separate stuck cylinders. If the a broken piece of ring is really jammed in there you may be in for an ordeal.

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The piston stops just with the bottom of the skirt flush with the bottom of the bore, so no go on that one. I have the head off, so the oil idea is worth a shot. Otherwise it's a large hammer and a load of swearing...

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with the carb and reed valve off you can't see through the intake port? You should be able to. If that's where the ring is catching you can push against it with a flat blade screwdriver. Sounds like an extra set of hands would be beneficial...

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The carb is still on it - this is on the crankcase. I can lift the barrel up from the crankcase but only until the crank reaches TDC, at which point the stuck piston prevents lifting any further. The piston is stuck around BDC in the bore. I guess I'm referring to the transfer port in the barrel to be strictly correct.

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I think juliend meant if you took the carb off the cylinder maybe you could see into where the piston was stuck. But looking at pictures on google it looks like the KDX125 is case induction? If so that is not going to help you.

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Yes, it's case inducted, so I can't see the inlet/transfer port at all. I can't get the barrel up high enough to get a good look from underneath and there's not much to see from the top other than the piston crown and two deep grooves in the bore.

On the plus side, having had to dismantle the engine has taught me a lot about how they work, especially the KIPS - I'm a noob when it comes to 2-strokes (which may or may not have led to this situation in the first place). But hey, at least I have a project now, and it won't happen again.

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On an old air cooled bike (yes I'm that old) that had the rings welded to the cylinder I had to remove the engine, place a block of wood under each side of the cylinder and used a hammer and another block of wood in the bore to beat the piston out. I took a couple of good hits and the piston was out.

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On an old air cooled bike (yes I'm that old) that had the rings welded to the cylinder I had to remove the engine, place a block of wood under each side of the cylinder and used a hammer and another block of wood in the bore to beat the piston out. I took a couple of good hits and the piston was out.
Hey, I resent that! That means I'm old too, because I've had air cooled bikes! 👍

🤣🙂:applause:

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On an old air cooled bike (yes I'm that old) that had the rings welded to the cylinder I had to remove the engine, place a block of wood under each side of the cylinder and used a hammer and another block of wood in the bore to beat the piston out. I took a couple of good hits and the piston was out.

I am considering putting some wood between the crankcase and barrel to lift it a little, then going at it with a mallet and block of wood from above - with the tank off there appears to be enough of a gap to get a good swing at it.

I once stripped an old diesel engine that had thrown a rod - one of the pistons had welded into the bore and I had to take a similar approach to get it out. On my bike it isn't seized though, just 'locked' into place by some unseen errant part.

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