I had that problem once when I went a little crazy with the blue locktight on the grub screw. I seeped down n between the pinion and shaft and that sucker was stuck on there. A cigartte lighter on the pinion and then carfull prying got it off though. just go slow and try not to overload the motor bearings while you are prying at it. A gear puller is the safe way to do it, but its kinda hard if you cant get the motor off o f the mount with the pinion on it.
I can't decide if its more fun
to make it...
or break it...
I haven't put a flat spot on my Neu yet. The pinion came off twice before I used loctite. So far no problems, but I am a basher. If mine comes off I won't lose a race.
I have used a soldering iron to heat the grub screw and then used a pinion puller to get stuck pinions off.
I have the Tower gear puller and it works fine. The only issue is the space between the sides of puller can only fit up to a 13T pinion (tried a 13T and it fit, with a tiny bit of space, so a 14T may work as well but it would be close). Anything bigger won't fit.