RE: RC Aerodyne 500 size Apache
I ended up turning the one way brg hold down .025 on the dia to fit the gear. I used a mini lathe bought from Harbor Freight. I left the main shaft cover installed in the on way brg hold & chucked up on it. (You could do the same thing by chucking it up in a drill press & use a file.) That gave me a really nice fit. I also had to drill out the mtg holes in the gear with a #40 drill bit & tap with a 3mm x 50 tap. I still need to ream out the smaller gear to 10mm dia, so that it will fit on the main shaft cover.