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CRF motor/gearbox locking up?

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Hi all,

New to the Honda and CRF sub forums.

I bought an 04 CRF250x over the weekend. I bought it because it was a rental bike that I was riding in SuperMoto practice before a race weekend.

In the 3rd practice, the rear wheel locked up and tried to spit me off, but I grabbed the clutch fast enough.

Back in the pits, the motor would not turn over on the button and the kick starter was locked solid at the top of its stroke.

I figured a valve seat dropped out and caused chaos (known CRF issues, right?) and that's what was locking the piston up. So I offered the owner a cheap price thinking this was my chance to get a race ready SM at a low initial investment, and bought the bike from him.

But the story get weirder today.

I began to try and figure out the extent of my damage...pulled the valve cover off and everything looks ok (it's hard to see the intake valves under the cam, but there was nothing out of the ordinary looking in the top of the head); took the spark plug out and it looked perfect, no aluminum deposits like 2 smokes get when the piston sticks. Top of the piston looks good (normal) from the spark plug hole

Hit the starter button by accident and it cranked over. Put the tank back on and I could not get it to run, but it cranked over just fine.

And then it locked up again after is sat for a while.

I'm getting a 10mm moto adaptor for my compression tester tomorrow, but if I can't get it to crank, that won't do me much good.

The really puzzling thing is that the bike won't start when it does crank and it does 'sound' like low compression when I crank it, but they're no evidence of overheating. Additionally, intermittent locking up is something I've never experienced before. 👍:worthy:

My question is, has anyone ever heard of this and/or have any experience with something in the gearbox or clutch or starter clutch f'king up in such a way that the motor locks up intermittently???

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better check your cam timing. The tensioner may have failed and caused things to go fubar...

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Better drain the eng oil to check for any fine metallic particles in it, that could be an indication that the bottom end is coming apart and causing it to seize.

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ditto on the cam timing. If the cam timing is off the piston will hit the valves causing damage to the valve train. Good luck

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is the tensioner a common failure?

as far as I can tell from looking in the spark plug hole with a flash light and looking at the spark plug, there doesn't seem to be any obvious piston damage

I'd hate to pull the head if I don't have to....many signs (locking and then unlocking) are pointing me towards the gearbox, except for the fact that it won't start again when it does spin over

feck!!! what to do, what to do???

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Not a common failure, but if the bikes has a great number of hours on it and was not rebuilt properly ie replacing the timing chain and tensioner then it could have failed.

Check the top-end first, it is easy to get too and you will need to get to it anyway.

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I hate to say it but having a loose chain and valve timeing jump bending valves would probably be your best case senario. It is never good news when a bike locks up. If you tensioner is damaged you can redo the top end and replace chain and tensioner....if it is not I fear major bottom end damage. either way goodluck

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^ totally agree...that is something I can deal with....if there's a gearbox problem, I'm gonna need some professional help...

the weird thing, which I've never experienced before, is the locking and unlocking...bizarre

anyway, haven't had time to futz with after the initial look-see, but as soon as I have more definitive questions and/or answers, I'll post back

thanks all for your thoughts..

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(Johnnyonthegaswife posting for Johnnyonthegas, who is too pissed to post.) It does not look like the tensioner - the timing is perfect. The gearbox oil didn't have metal particles in it. We'd check the compression, but the 10mm adapter JontheG got for the compression tester is not long enough to thread into the spark plug hole.

Putting the bike in gear and rolling the bike backwards slightly unlocks the engine and allows it to spin - every time.

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starter broken and staying engaged in the motor???. try taking the starter out and kick starting it. I dont know much else unless you take the side cover off and inspect. Wouldnt worry too much about the compression...I would just concentrate on getting it not to lock up while cranking.

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Not a whole lot of experience, but it seems like maybe one of the gears retainers has broken or come loose since rolling it backwards seems to realign it temporarily, and it did lock up while riding it. Ask the seller, he may have some insight to the problem since he took the offer so readily. Not that I think he would be forthcoming, but he might.

What about the starter gear clutches?

After you get it unlocked by rolling it backwards, does it lock up again when you roll it fwd or when you try to start it again. If it locks on the roll I would lean towards one of the tranny gears.

And if these questionsdon't help directly, maybe they will spark something with the guys who are smarter than me!

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I want to suggest again to drain the eng oil and check for metal particles, also remove the oil filter and check the outside of it for metallic debris.

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