Military Action Titanium Piston Jamming
 

I've recieved my new parts from Airsoftparts.ca (excellent service BTW), and one of these parts was a Military Action aluminium piston with full titanium teeths. I rebuilt my gearbox (PGC V3 gearbox for TOP M249) and what's happening is that the motor & gears are fully cranking the piston, and the gears continue to spin, but the piston stays back, fully cranked (with the gears making an awful grinding sound.

I know that the gear timing / shimming / overall installation is perfect, as the whole setup works perfectly with another piston that I had on hand.

Any reason why such a thing would happen, do I need to go some filing and/or grinding on that piston for it to work properly?

MODS : Please feel free to move this topic into the Doctor's Corner if needed, as I wasn't sure of the right location.

There's a thread right now on the go about somebody's v2 locking up...take a read through that...it'll hit all the same things that are going to be suggested here.

I've read that post, but my symptoms are different : My piston fully compresses the spring and clears the sector gear (barely, hence the light grinding sound). It's just not coming back like if something was preventing it (dimensions, metal burr, no idea..) from "firing".

Some brand springs jam up on the spring Guides. The walls of the new piston is thicker so less room for the spring to expand. this is my best gess.