[yuhaoyang]

after a TM hits around 330 with an upgraded spring, it will(theoretically) require metal bushings, around 370ish it should(theoretically) have a good spring guide, reinforced gears, and a good cylinder head. A sorbo is a very good idea as well since the mechbox shell isn't reinforced. Although I've heard that "samuel" on EAR pulled off some witchcraft and made a stock TM shoot 340 with no aftermarket parts. It also seems some people have run high(er) spring powers on a TM with mostly stock parts, and they've run in to no issues.
Don't bother adjusting the motor height, since there isn't really anything wrong with it. Changing from .2 to .25 is equal to around a loss of 30-40fps.
Opening a TM when you havn't really opened a mechbox can lead to a world of headaches... I've done that before, and it was a pain in the ass... Well, if you still want to open it, good luck!