upgrading my ak 105

[moaner]

after some probs I am gonna upgrade my mechbox. last time I opened it I noticed that my nozzle wasn't comming all the way back and 2 bushings were broken. shot 2 mags with my new 11.1v lipo and the piston is now shredded to pieces.

so I ordered: ak nozzle with o-ring
new tappet plate
v3 pistin with alu teeth
6 mm steel bearings
ars mask 3g force

so I have normal dboys gears, a magnum motor and a v2 madbull python
my hop up is a blue madbull with a little teflon over it.

now, for the mask pistonhead and cylinderhead they recommend to take away the last teeth of the piston. does somebody has some experience with that?
what caused the old nozzle to not fully pulled foreward again?
and what spring should I use my new 100 or my current 120? I do not play here on public fields.

hope to get some help here.