View Full Version : bolt carrier gas piston pin

08-15-2014, 06:03 PM
this incident happened on my Yugo M70 B1 but i would bet it is generic to all AKM's. maybe?

well anyway i had the Yugo out yesterday, along with a Romy folder, and the piston pin decided it wanted to try to drift itself out and got hung up on the gas tube causing a failure to go into battery. the pin is loose enough to move back into place with your finger so i pushed it back in and tried to run the rifle again only to get the same failure.

my question is how detrimental would it be to run the rifle without the pin in place? i have other bolt carriers that don't have a pin in them, like the Romy, and they run just fine. then again the other carriers may have the piston LockTite'd in. in fact i swapped the carrier from the Romy into the Yugo so i could play with it (it's easier for me to bump a full stocked rifle :)).

on the other hand how would i go about locking that pin back into place? could i try to center punch it and maybe get the ends to spread just a bit to hold it in? i have a welder but i'm not that precise with it and i doubt standard solder would stand up to the heat.

too bad the old build forums are gone or i probably could have answered this in a quick search.

any ideas guys?

08-15-2014, 07:35 PM
I would first try staking it in if you could not just weld over each end so it remains captive.

Century was notorious for installing the piston and welding it in place, which as long as it was almost perfectly aligned was ok, but with all the movement of the carrier, a loose piston is needed, which is why the Kalashnikov was built that way.

A properly installed piston is turned in by hand until snug, then backed out about 1/2 to 3/4 turn, then drilled and pinned in place. Most rifles have the pins installed, then the ends are welded over and the welds ground down to be flush so that they don't catch on anything.

Since you have a welder, you really don't have to be perfect. Just get enough weld over the end holes to keep the pin in place. I would try center punching it as well as you state to try to get it stuck in the assembly, but still would go ahead and weld over the end holes. Or as some rifles are, they are just drilled from one side, so welding the hole blind pins the piston in place.

How ever you do it, you still want a little slop in the piston. With all the slop in all the parts of an AK variant, it is amazing they function, but that slop is why they are so reliable under the worst conditions.

08-15-2014, 08:33 PM
I guess this would be something some of us need to address and inspect?

08-15-2014, 08:42 PM
thanks for the idea Nut, i will give the weld a try here in the near future.

incidentally this piston has zero slop yet is pinned in unlike ANY of the other carriers i have (of which i have two spares). none of them have any slop but are just threaded in and not pinned, as in you can see threads through the pin holes in the carrier. this leads me to think that since the Yugo was built on a US receiver, Century didn't bother with putting a US piston in. i could be wrong but who knows for sure?

and it's funny because before i left for the shooting trip i looked at one of the spare carriers sitting on my gun bench and thought to myself that i should toss it in my tool bag just in case i needed it. shoulda, woulda, coulda i guess! it would have saved me some grief that day for sure.

08-15-2014, 10:01 PM
The ones that I have seen that were blind pinned, the hole on the other side of the piston was obvious, and you could see the threads inside, but on the other side the weld was so well smoothed over that it was almost impossible to find. Century, as well as others saved time and money by just drilling far enough into the carrier to press the pin in from one side, then weld over it to keep it in place. Sometimes they got lucky and the piston had a little slop in it, but many times it was solid.

I have one Chinese rifle that the piston is so loose you would think it would cause problems, but it hasn't.

I wouldn't be surprised to see someone build a rifle with the red loctite on the threads pretty much gluing the piston in place. Doing it wrong is the easiest way to put one together, doing it right just makes sure the rifle will be reliable.