M4 gearbox problems

captain wow

I got a broken M4 off a guy I work with in the hope of being able to fix it up. At first there just seemed to be a problem with the electronics but I fixed that and now when I try to test fire it the gearbox jams up and the piston is stuck back to the rear. Not sure what's causing it, it was my first time to open a gearbox but I'm pretty sure I'm putting it back together properly. The only thing I've noticed is that the air nozzle doesn't seem to move back as far as it should i.e. it doesn't seem to move back as far as the tappet plate needs to move. Would this even cause the gearbox to jam up?

Does anybody have any ideas how I should go about fixing it? Should I look into getting a new gearbox or just scrap the gun altogether? The rest of the gun is in great shape and he gave it to me for nothing so I don't want to give up on it. I found this gearbox (http://fire-support.co.uk/product/marui-m4-mecha-box-assy-without-motor) but if anybody has a spare gearbox in good condition I'd be willing to buy it off them.

Assistance would be greatly appreciated!

DeBurca

Sounds like a simple gearbox lock up, get a fully charged battery (9.6v would be bes)t and select full auto and fire
90% of the time it will simply free itself, assuming that you have reassembled the box properly

captain wow

DeBurca wrote: »

Sounds like a simple gearbox lock up, get a fully charged battery (9.6v would be bes)t and select full auto and fire
90% of the time it will simply free itself, assuming that you have reassembled the box properly

I've tried that a couple of times but it hasn't worked so far. any other suggestions?

DeBurca

captain wow wrote: »

I've tried that a couple of times but it hasn't worked so far. any other suggestions?

Get a long thin rod/screwdriver and insert it through the air nozzle and push the piston all the way back
You need to do this sharpish so as to spin the sector gear clear of the last tooth of the piston, if you do it slowly it will catch the last tooth and not release
If that happens then you will have to remove the motor and grip to manually move the anti-reversal latch while pushing against the piston

captain wow

Thanks for the advice deburca but i've given up on the damn thing! I've tried about everything i'm capable of trying and it still seizes up. Ah not to worry, I can use the M4 for parts.

DeBurca

If you are ever down my part of the country side, maybe going to LAC or whatever bring it with you I would be happy to have a look at it for you