CR125 Clutch removal

Question on a 1998 CR125: I'm replacing my right side crank seal.
After I removed my clutch disks, there is a large nut I have to remove
on the main shaft. How do I lock up this shaft so it doesn't spin with
the ratchet? I put it in gear, but it just spins the rear wheel. I
don't have air tools to spin it off. Any recommendations?

Just temporarily hook up the rear break pedal, step on it with your foot
while loosening the nut. Done.
Jerry

I tried that...That nut is really on there. I was stepping so hard I
was worried about snapping off the brake pedal. Any other
recommendations?

I broke a clutch basket once, trying to jimmie up something. MotionPro makes a
nice clutch holder that works perfectly, looks like a vice-grip with long
90-degree jaws. Not that expensive (compared to breaking a basket or a caliper
carrier) most places like Cycle Gear have them in stock.

Put the bike in 4th or 5th gear and try it, less mechanical advantage -
if that doesn't work you're going the wrong way.
Jerry