I've been turning wrenches on dirt bikes a long, but the sprocket counter shaft retain nut on my '06 KLX250 was the tightest I've encountered. The bike only had 4.5K miles when I bought it this summer & I'm sure the PO never removed it, but I decided to install a 13t sprocket. After flattening the splined washer good, I first tried an 18" breaker bar with a 36" cheater. No way. So I pulled out my trusty Chicago Pneumatic 1/2" impact gun (max torque 525 lbs). Wouldn't budge it! Holy crap (I thought), what now?! So off I go to United Rental to rent an Ingersol Rand 3/4" impact gun (max torque 1200 lbs) and I heated the nut first with a propane torch! I thought "Take that, you dog!!!!" But the IR could not budge the bolt a single nanometer!!! I couldn't believe it!!! That thing should've twisted the end of the output shaft off!

After scratching my head (and the other end) for a while, I decided to cut the dang thing off with a Dremel. That did it, but I still needed the 1/2" impact gun to spin it off even after I cut it nearly through, and I damaged the output shaft threads slightly with the Dremel in the process. Shoulda been a bit more careful I guess . It's hard to believe the factory installed that bolt so tight. I guess anti-seize really is your friend.

 

My thinking is someone put lock tight on it, or heated themselves and made it worse.

 

I think 98% of them are on tight, but yours is the worst Ive heard of. After I finally got mine off, I used anti-seize when re-installing, and have never had a problem since.
Glad you got it.
Dan

 

Wow that is crazy! Mine came off instantly with my cheapo Harbor Freight electric impact gun.

 

Certainly a worthy horror story!
Mine took a 4 or 5 ft cheater bar.

 

Same here. I'm a strong believer in impact wrenches, but I tend to err on the overly protective side concerning the tranny internals. I worked at a shop and saw/used impact wrenches on troublesome countershaft nuts. Never saw a serious issue except in one instance of a stripped output shaft...a weird oddity. Those cases at the shop were not my bike. I prefer the serious cheater bar approach. Put a strong tube/pipe in the brake rotor and across the swingarm to hold the chain static. I've also seen a block of wood jammed into the front of the swingarm between a knobby tire and swingarm.

 

I don't know what it is with that friggin' nut, but even after making a conscious effort to not tighten it to much and let the lock tab retain it I'll be damned if it still fought me and my 600lb/ft IR gun. The only thing that seems to help is a liberal dose of penetrating oil before. Still scratching my head...

 

Mine came off easy enough with a local garage's impact, but after I put it back-tightening it by hand, I added a white stripe across the shaft and nut (cs cover is off) and I visually check it often. It's been about a year and it hasn't budged

 

Yea, I'm with you on that. I have good reason to believe that nut had not been removed since the bike left Japan in a crate. It's like it tightened up in service, although I don't see how. Far as penetrating lube, I covered it in PB Blaster for two days prior. Made no difference at all, that I could tell. As one poster mentioned, I thought for a while it had been red locktighted. That's why I heated it before the 3/4" IR gun removal attempt. But after cutting it off, there was clearly no evidence of thread locker. It's a conundrum, for sure!

I'll try Richard's suggestion of witness-marking the nut after I get/install the new one. Thanks Richard!

 

Yep, tried that same technique with my 18" breaker + 36" section of 1" pipe. I ended up picking the bike completely up off the floor onto the front wheel, with the OL sitting on it, with the bar. With no other effect other than scaring the OL. In many years of car/bike work, that's the first nut/bolt I've been unable to remove with with this wrench combo (that I could reach with it). Was the only way I could remove the massive 5th gear output shaft nut in the primary drive on my Harley Dyna. I generally prefer not to use an impact gun if avoidable, as it puts such a shock strain on the shaft/mechanicals attached to the nut. Using the impact gun once on my Harley primary nut caused the magnets to dislodge from the alternator rotor.