Wasn't this posted in RC Groups?

I'll post this in here for those who don't look over there.

Pinions yet again: this has been covered so many times - please use the 'Search' function and you'll get the answer almost every time.

Tried and true - works every time

Others have had success with green loctite 638. However, I have not been too impressed with locktite in these circumstances, but I have had great success with soldering pinions on.

Use a brand new pinion! (Re-used ones have been 'stretched' and will not have the correct interference fit).

Use plenty of flux and apply a thin veneer of solder to the roughened shaft. Make sure you get some flux into the hole in the pinion. Align pinion on shaft and, while applying heat from your soldering iron, ease it on with gentle pressure, between the jaws of a small vice (use a spacer nut/sleeve against the pinion at the front jaw, and have the other end of motor shaft against the rear jaw).

Cheers, Phil