Originally Posted by TomB

this is one of the drawbacks of forums, it's hard to find info, so people inevitably have the same issues, ask the same questions and get the same answers. Maybe a webpage with a 1 page solutions guide would be easier lol...considering the heartache this issue is causing some people. Maybe this issue is caused by a quality control issue on mugen's end?

-no tight side belt
-shim the 1st and second gears with a .1 to .2mm washers
-get rid of roller on 2 speed, use long grub screws only
-setup 2 speed shoes so there is .05mm gap between 2 speed cam and the shoes (ie this will give a bigger gap between the show and the housing...give it a go).
-make sure both shoes have the same 2 speed release setting (screw you adjust to alter for or after 2 speed shift point)
-heat the gears up so that when you screw the housings on you do not warp the gears
-check gears roll on shaft true (ie do not wobble when rolling). if not, re do above step or pre tap gears and use loctite 222 threadlock on the screws and the plastic. Never overtighten screws on the housings as this will cause warping.
-mesh engine with larger spur gear off. this is the gear that needs to be well meshed. mesh it so it rolls free without weird noises and with as little gap as possible
-use locktight on engine screws every time you take screws out and put back in (use loctite 222)
-consider using loctite 222 to seat the bearings into the plastic bushings, and loctite the plastic bushings onto the baulkheads to avoid movement or minute vibrations that could cause wear to parts that require exact fit and finish.
-use good quality bearings on the 2 speed shaft and keep them oiled. check for wear (ie side to side, in or out play)

if still having issues, check parts like bearings and shafts for consistent size.

you don't need an engine brace, or anything like that.