ics m4 problem

[zach57]

I recently replaced a piston that chipped during a game with a metal tooth piston. Whenever I put the upper gearbox in the reciever and connect it to the lower I hear a mid-pitch grinding sound when i pull the trigger and the piston is not pulled back at all, but whenever I take the upper gearbox out of the reciever and connect it to the lower it shoots fine.

Any solutions?

[Vulpes]

Split gearbox... seemed like a good concept.

I don't have experience with these myself, but try giving the upper receiver a good inspection with the gb in it. Make sure everything is in place and correctly aligned.

Not much help, but hopefully you can find something you missed earlier. Also try looking at disassembly/reassembly guides on forums and YouTube.

Good luck!

[Cosmos]

The pressure exerted by you just holding the gearbox halves together might not be the same as the upper and lower receivers pinned shut. Have you compared the height of the piston and the piston teeth with the original part? Is the new one even nominally taller? Maybe the plastic piston teeth had a little give and the metal doesn't give so much and grinds with the gears. You might want to try a another piston with plastic teeth.