The "joys" (aka. trials) of being a gun doctor!

[Red62]

AHAHAHAhahahahah!!!!! As much as I LOVE drywall screws, I think that's a little too far with replacing pins with them. That made my day.

[Styrak]

So I got a King Arms Thompson M1A1 and mags for extremely cheap, with the knowledge that "something" was wrong with the gearbox, and that it was locked up. OK, will have to open it up and fix whatever is wrong, possibly replace parts.

The piston head was not attached to the piston, but the peculiar part was that it was BACKWARDS inside the cylinder. So it somehow got flipped around, and also I think the piston head screw had jammed up the gears which is why it wouldn't cycle at all.

But in the end nothing else was damaged, just had to clean it out from all the plastic bits from the destroyed piston head, put in a new piston head, shimmed it, and put it back together. Not too bad for a dirt cheap gun.

[AuroraUnit117]

So i was testing a gun for a customer...when suddenly it started shooting full auto on its own....what the hell. So i rush to remove the battery then proceed to take it apart...

This is what happened. that tiny pin on the trigger trolley came out(check out how burnt it is), and somehow managedto , instead of falling into the shell or out the trigger hole, get wedged between the trigger contacts by some miracle. I wish i had taken a picture of it stuck in there but you get the idea. Even better yet, the heat generated by this metal piece somehow managed to heat up the cylinder so much the o ring melted, then must have busted when it was cycling as i frantically tried to remove the battery. Million in one chance.

[pestobanana]

Originally Posted by AuroraUnit117

So i was testing a gun for a customer...when suddenly it started shooting full auto on its own....what the hell. So i rush to remove the battery then proceed to take it apart...

This is what happened. that tiny pin on the trigger trolley came out(check out how burnt it is), and somehow managedto , instead of falling into the shell or out the trigger hole, get wedged between the trigger contacts by some miracle. I wish i had taken a picture of it stuck in there but you get the idea. Even better yet, the heat generated by this metal piece somehow managed to heat up the cylinder so much the o ring melted, then must have busted when it was cycling as i frantically tried to remove the battery. Million in one chance.

And that's why MOSFETs are a thing that should be used.

[AuroraUnit117]

Mosfet would have prevented the heat but the full auto thing would have still happened. It was bridging the contacts. The mosfet would have thought the contacts were being connected by the trolly and the same thing would have happened....just without the meltyness hahaha

Originally Posted by pestobanana

And that's why MOSFETs are a thing that should be used.

[pestobanana]

Originally Posted by AuroraUnit117

Mosfet would have prevented the heat but the full auto thing would have still happened. It was bridging the contacts. The mosfet would have thought the contacts were being connected by the trolly and the same thing would have happened....just without the meltyness hahaha

I was assuming the heat contributed to the pin coming out.

[AuroraUnit117]

Naw it was just a shitty ACM trigger set haha The pin fell out first, then somehow got stuck in the contacts, thus bridging the contacts and making things melt. The cycling got worse sounding as i was trying to take the battery out. It would have been the o ring melting haha

Originally Posted by pestobanana

I was assuming the heat contributed to the pin coming out.

[Spike]

Close enough?

[lurkingknight]

what am I looking at?

[Spike]

Sector gear teeth stick out so far they bind up the piston. Sigh.

[HKGhost]

Originally Posted by Spike

Close enough?

LOL. Good'ol ACM

[lurkingknight]

oh that makes sense now. lol. bad castings are everywhere.... I have a CA v3 just off the bench where the gearbox shell halves don't line up.. but it works.

Pulled apart a brand new aps m4 and the rubber pad on the cylinder head wasn't even attached... it didn't even fit into the indent for it. AY m4 with a half width piston rack meant for super torque gears.

[RainyEyes]

Originally Posted by Spike

Close enough?

How would one fix this?

Would you just replace the whole gear set or would you actually try to sand it down with a dremel?

[lurkingknight]

changing the gear profile might fuck up the meshing. I would count the teeth and replace the sector if you've got one laying around that matches... if not... replace the gearset as the proper fix. Sanding might work, or instead of wasting an hour or more with assembly/disassembly cycles trying to test it, just put in a JG 18:1 set for stock gears, then you know the gearset will work.

[Spike]

Yeah, other 18:1 gears didn't mesh properly. Ended up swapping the whole set. It's a personal gun anyway, so no extra labour charge to anyone. Those were also the stock CA gears :S
I noticed there was an issue when I went to test the piston movement in the gearbox shell, and the sector gear moved despite the half teeth not touching the piston.