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'05 YZ250F Stator woes

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My freshly rebuilt YZ was running funny, backfiring and such. I suspected the timing chain was loose or had skipped a tooth so i removed stator side cover. The nut that holds the rotor magnet to the crankshaft was completely loose... ok that makes sense. I completely removed the stator to inspect it, replaced it and the magnet, and put the nut on with some red locktite. I waited 24 hours for the locktite to set. I came back the next day to test ride it and I kicked and kicked but she didn't want to start... I have heard to remove the stator again and sand it with some very fine grain sandpaper and try again. Any other advice would be greatly appreciated.

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Whoa Dude,

You may have a problem but I think you just compounded it by RED Locktiteing that nut on there.  It takes heat to get RED to loosen up.  When you add flame to the shaft to get the nut off, you may cook the new stator.  And no, I have not been able to get one off with a heat gun.  Just be aware, this may not come out good.  Did you lather it up with RED, or just smooth a little onto the threads with our finger?   Less is more chance to get it off in this case.  Just wondering.....   And it needs to come off to check the Woodruff key to see if its sheared causing off timing.

Simple stuff first.  Have you pulled the spark plug to see if you have spark?  Have you loosened the carb bowl screw to check fuel flow?  Do you have fresh gas?  Have you checked the timing mark on the flywheel and checked TDC against the mark to see if the timing mark doesn't match TDC with the piston?  Good news is: If piston is at TDC and timing mark lines up, Woodruff key is not sheared.  Did you check the pilot jet to make sure it was clear, not stopped up?   In my mind the magnets might still be in question until i was able to inspect them.

As far as sanding the stator, thats what you do with a mag and coil on a Briggs and Stratton lawn mower, but not a stator that runs in oil, unless the new one you installed was rusted when you installed it.

When you said replaced the magnet, what do you mean?  Most of the time when you do that, you replace the flywheel.  If the magnets have come off, that's what I would do.  If they came off once, they'll do it again.  And I'd be wondering what damage and what metal is still in the motor.  You better consider pulling the gear/rotor oil pump and see what scoring if any is there from metal in the oil, and drain the current oil and strain it to see if there's metal in it.  The good news is there's a screen inside the case to catch big bits.  More investigation needed    .............. is what I'm thinking.

I know this is a lot to think about, but some soul searching and research is in your future.

Edited by ronbuell

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Well luckily for me I just used the tiniest dab of locktite. Im 100% sure the key was in there and installed correctly before I put the nut back on. I have checked for fuel flow and I do have good flow, the gas is mabye 2 months old (just got home from deployment) but it is 93 octane. Carb has been cleaned recently (before I left). I will take the nut off again and pull the rotor to inspect the stator again. I will also inspect the oil pump and check the strainer. Luckily this was immediately an apparent issue when it happened and the bike mabye ran for 30 seconds with that nut loose so the metal in the oil should be minimal. the nut and everything near it was not beat up at all. Hopefully the nut comes off without too much issues. Is an electric impact a good idea for this?

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got the nut off with no drama. removed the magnet from the stator. checked for any irregularities on both stator and magnet. none noted. replaced magnet and reassembled. still wouldnt start when kicked. removed spark plug and tested for spark... no spark. at all. it ran before i removed the stator and when i put it back in it has now lost spark. I didnt do anything incorrectly in removing the stator what could have happened?

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Magnets have poles; north/south.  Most likely you put a "magnet" on in the opposite direction.  I was working on a starter once and installed it backwards.  When I tested it, it ran backwards.  If you put your magnet in backwards, N where S should be, S where N should be, the other magnets are pushing current in one direction, and that one is pushing current in the opposite of what it should.  Take it off, turn it 180 degrees, reinstall.  NOTE: it must be the magnet that you moved in the first place.

But there is still some misunderstanding on my part.  The magnets USUALLY do not come off the flywheel.  The stator is the part with the 4 poles, coated wire wrapped around each pole, windings connected, and wires connected in a sheath going up to your CDI.  Magnets are mounted to the inside of your flywheel, and when installed on the crankshaft, rotate around the outside of the stator creating a current in the windings.

Personally, I would not trust  a flywheel that the magnets have come off of..... just me.

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im calling the flywheel the magnet i guess. none of the magnets were removed. i plan to chase ground wires and check resistances later this week. hopefully it is something simple and not needing a new stator now. 

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Ok, relieved now.... thanks.

I've got a WR that's giving some stator issues too.  Check the point where it goes thru the case.  There's a grommet there that can sometimes get cut, or worn..  Run the length of the wires out to where they connect in.  May be as simple as ground like you mentioned, or dirty connector.  Substitute a new spark plug, or just make sure when you test that you ground it properly, not on the plastic valve cover... bolts are good to ground on.  Blue snappy spark is good.... you know that.  Check the connector on the coil on plug that there's no dirt in there.

I have not had a bad CDI, but I have had bad coil on plug coils.  Substitution for know good is the only way I know of to test those.  Good luck with it.

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