Thanks for a the suggestions guys!

I finally got it all assembled last night with the help of some rare earth magnets. Then did the test fire and nothing. BB rounds aren't flying at all. Ugh, dissemble it again and I noticed that I didn't put the nozzle on the tappet plate. Stupid mistake. Another 30 minutes later I got it assembled it again and now it's fully working.

Thanks guys!

The only good thing is that after trying 100 times you start to get to know everything pretty good. Experience is the key with mechboxes.

A good trick I have found for keeping the gears in place is a strong magnet ( I use an old harddrive magnet ) on the back of the gearbox. It pulls all the gears down in to their bushings/bearings. Can hold the mechbox upside down without anything falling out.