Yesterday i spent 5hours fixing my printrbot simple so I could go on my self with the gearbox and the new motor. I got almost the same motor speed as before with no smoking motors. But this time I blew off a capacitor on an arduino by not giving attention to the poles. Gladly I was able to rip it off and place a new cap on there. I still have to use a motor bridge or a pwm control.
So here are some pictures of the gears I imported from svgs me and someone on wikipedia did.
And the spacer for the gears. I think I have to reprint it though and make it almost closed on one side, so only the 4 toothed gear will stick out.
I used my soldering iron for welding.