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1996 KX250 crankshaft not spinning

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Hello everyone, my brother recently bought a 1996 kx250 project bike that when received was an engine in a rolling frame. When the bike was first bought the engine turned over smoothly but wouldn't shift, but upon further looking it was because the shift shaft was improperly installed (was missing the collar that holds the spring and was jammed between gears). Removed and reinstalled the shift shaft and now the bike will no longer turn over. it has a little movement back and forth like it wants to make a full rotation but will not, there is no chain connected, no clutch assembly connected (removed to install shift mechanism) and the cylinder is pulled off because it needed a base gasket. so any advice is well appreciated, like i said the bike turned over very easily before the re-install of the shift mechanism. Will try to provide video/ pictures when i can thank you

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possible something either fell in the crank or was already in there and just now jammed it?  another possibility could be the water pump being jammed

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If the clutch basket is removed, then the crank should spin freely. Since you do not know the history of this bike, do you plan on splitting the cases? I would.

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Alright so now the crank is now spinning and it is spinning pretty freely too, while it was "seized" i added lubricant all over because my first thought was this bike sat so long that rust had built up somewhere and was jamming it.. it was has been right around a day and a half days since i had it soaking in lubricant and it is now free. Still unknown for 100% what the issue was and would like to do a flush of the cases. Any advice/detailed instruction on that would be great. We would prefer not to split the cases, especially now that it is spinning and I don't here any strange noises like grinding or something hitting something else.

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If the clutch basket isn't installed, the crank won't spin because the basket has a gear on the back that meshes with the crank gear to make the crank spin

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Tried turning it over with basket, without basket, and by the stator. Not that it matters now, it spins freely

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When you put the cases back together you get binding on the crank.  Just take a hammer and lightly tap on the ends of the crank, that will free it up.

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You need to check the crank for damage. With the top end off, check to see if the crank moves up and down at all. Side to side is okay but up and down means it's time for a new bottom end. Until you do this you are guessing at what could be wrong. You already know that a previous owner improperly installed the shift mechanism, who knows what else was messed with. Get a shop manual and go over the bike carefully. 

Have you had the engine running? Sounds like you haven't. With a used bike that is bought as a project (unknown history), I always assume the worst until proven otherwise. Inspecting the top end will tell you a bunch as will any crankshaft movement. Any chance you can post pictures of the top end? Just a thought.

Good luck with the rebuild, let us know how it is going.

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You need to check the crank for damage. With the top end off, check to see if the crank moves up and down at all. Side to side is okay but up and down means it's time for a new bottom end. Until you do this you are guessing at what could be wrong. You already know that a previous owner improperly installed the shift mechanism, who knows what else was messed with. Get a shop manual and go over the bike carefully. 
Have you had the engine running? Sounds like you haven't. With a used bike that is bought as a project (unknown history), I always assume the worst until proven otherwise. Inspecting the top end will tell you a bunch as will any crankshaft movement. Any chance you can post pictures of the top end? Just a thought.
Good luck with the rebuild, let us know how it is going.

Already check the crankshaft and it has no up and down play at all, very little side to side, as stated I was able to turn the engine over and once again and examinted the crank itselve and there is no markings or anything. Look really good. I put some oil in the bike and spun it over and drained it, some yuck came out but nothing major. Without having to split cases I think we may take the gamble on this one

Sent from my SAMSUNG-SM-J727A using ThumperTalk mobile app

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Good news on the crank, hopefully all else is well. Will be interesting to see the results. Best of luck with the bike.

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Good news on the crank, hopefully all else is well. Will be interesting to see the results. Best of luck with the bike.

I think the results will be interesting aswell, but as of now everything else seems okay bench test wise. The bike will now shift, it spins over very easily, and the crank itself is okay. I think I will have the bike put together fairly soon, just waiting on a few parts. I will post results when i can

Sent from my SAMSUNG-SM-J727A using ThumperTalk mobile app

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