ICS M4 Gear Grinding Again!
 

OK I decided to fix my friends ICS M4 C-15 Fixed stock. There was an awful grinding noise so I reshimmed it but the result was the same, it was a grinding noise in the gears I don't think they were even moving but the motor was grinding I believe but the gears were not since the piston was not moving.

when I split the gearbox and fire it, the gears move hmmm.

HALP!

I also tried motor height.

Stripped piston or gears?

I'm having the same issue working on a client's ICS, no stripped piston/gears/pinion/ everything is perfect.

take the upper off - place your finger on the sector gear, apply some pressure (resistance) and fire it and see if it spins... it could be the pressed gear on the bevel gear that contacts the spur gear...

5$ it's the bevel two parts gear that is broken loose.

Take a flat screw driver, lock it into the sector gear to prevent any movement. Press the trigger for a very short time. If the gears don't move BUT it grinds, it is the bevel.