Gas Piston replacement

[Hrothgar 0]

Hello all. I'm looking for any tips and tricks on replacing the gas piston on a Saiga-12. For various and sundry reasons, I've elected to go that route for compliance parts. I have already acquired a most excellantly crafted piston from HotBarrel.

 

Now, thus far, I have heard the process described as "drill out the 'dimples', unscrew the piston, screw in the new with loctite" HotBarrel suggested drilling through the new piston as well and installing a rivet instead of loctite, to make sure all stays put better.

 

Any suggestions what size drill to use? What size/type of rivet to use?

 

The 'dimples' on my bolt carrier are 0.145 inches in diameter. Do I want a drill approximately that same size, EG, to drill out the punch depression entirely, or can you get away with using a smaller size and have some of the depression left for a counter sink?

 

I have browsed a few other online forums and though many have topics dealing with removing/replacing gas pistons, they are almost universally for standard type AKs that have a roll pin/rivet in place already. Any information would be most appreciated.

[McUZI 1]

Just wondering what made you choose the piston over other compliance routes?

[stokstad 4]

I think it would be best to drill the dimples out completely if you dont you stand the chance of goobering up the threads and that would suck. I know that this has been covered before but i am too lazy to look it up. Do a search and or ask Cobra76two he replaced his piston on his S12 conversion.

[TonyRumore 1,332]

The gas piston is actually in the gas block manifold, similar to an M60 setup. The piece you are talking about is a bolt carrier extension in the Saiga design.

 

Maybe the ATF sees it diferently............

[Cobra 76 two 2,677]

I just drilled out the dimples with a 1/8" bit. Got a piston or carrier extension or whatever you want to call it from hotbarrel. Screwed it in to where it was the exact same length as the old one with locktite on the threads. Then I used a punch to flatten the threads on both sides and around the holes in the carrier. I have put many rounds through it and it has not budged.

[Hrothgar 0]

 

Here is a comparison photo I just took. You can see the stock carrier above, and the as yet uninstalled piston/extension below. The red dot denotes the location of the 'dimple' (It appears towards the top of the carrier simply because of the angle the photo was taken at. The heads are also roughly even.)

 

It appears that perhaps the replacement is a bit short? That is, if it were screwed in to the exact length of the current one, it would be too short to be drilled through and riveted in the exact spot where the dimple was drilled out. How sensitive is the gas system to the over all length? That is, if the new piston were screwed in far enough to be safely drilled and riveted, would that compromise the system's function?

 

As to why I chose to replace the piston - I elected to go with one of the Ace Saiga stocks rather than do a conversion. For my own preferances, I feel like leaving the gun mostly stock in that regard, I'm not up to drilling the reciever and installing a new FCG, etc. Thats just the route I felt most comfortable with. Flame on.

[Cobra 76 two 2,677]

It appears that perhaps the replacement is a bit short? That is, if it were screwed in to the exact length of the current one, it would be too short to be drilled through and riveted in the exact spot where the dimple was drilled out. How sensitive is the gas system to the over all length? That is, if the new piston were screwed in far enough to be safely drilled and riveted, would that compromise the system's function?

<{POST_SNAPBACK}>

 

I wondered the same thing because I think the threaded part on mine should have been longer too. But it was long enough to thread in past the hole so I didn't worry about it. Have you emailed hotbarrel and asked him about this? He turns them on a lathe himself so he may be able to make them longer. Maybe he just isn't aware of it. Anyway yours looks different than mine so perhaps you could have gotten the wrong piston? He does make them for all kinds of guns. Here's what mine looks like next to the old Saiga one.

has anyone else experimented with changing the length? It wouldn't hurt anything to screw it in a little farther with some blue locktite and test it out would it?

[TonyRumore 1,332]

The gun would probably run with the shorter extension, but it probably won't cycle with as much force as a long one. The gas piston in the manifold could either be forward in it's bore, or back against the carrier extension when the gun fires. If the piston is rearward, then you simply have a shorter "throw" on the extension as it is drivern rearward. If the piston is forward, then it gets a long running start and then slams into the extension at high velocity, momentarily stops as it overcomes the inertia of the carrier, and then is driven back with the short stroke as mentioned above. I would get a longer extension.

 

When you install the extension in the carrier, you should first turn the gas regulator in all the way, and then back it out to the first position, whether it's #1, or #2, is irrelevant. Then insert the carrier assembly and unscrew the extension until it does not quite let the bolt go completely closed. Then screw the extension in deeper a hair at a time until the carrier bottoms against the trunion. It will hit on the left side. That way the gas piston does not get a big running head start and slam into the extension each time the gun is fired. I wouldn't sweat screwing with the dimple at all. Just put some red locktite on it and it will be in there forever.

 

Tony Rumore

Tromix Corp

Edited August 16, 2005 by TonyRumore

[twinhairdryers 2]

I disagree on the short stroke leading to cycle problems. Isn't the idea behind drilling out the gas port holes to increase the volume and rate of gas into the gas chamber to create more gas to run light loads? If you had a shorter gas rod, you automatically start with a larger chamber to hold more gas volume that may send the bolt back quicker and hold it back for longer than a stock rod. It may actually work better for cut down barrels to cycle light loads.

 

I could be just stupid though. let me know.

[TonyRumore 1,332]

You're thinking that the carrier extension piece shown in the pics above is being driven rearward by direct gas impingment like in a standard AK-47 setup. The Saiga is completely different. The "gas piston" pictured is not a gas piston at all and see's no direct gas pressure. It contributes nothing to the volume of the gas chamber/manifold in the Saiga design. There is a seperate gas piston that slides back and forth in the manifold that drives the extension rearward.

 

I don't want to stir up a pile of shit here, but we need clarification from the ATF as to which piece they consider the "gas piston" as far as U.S. compliance parts are concerned. Technically speaking, the gas piston is the 1/2" thick nickel sized disk that resides within the gas manifold, not the carrier extension that is being changed out as shown above. In the AK-47 design, the extension rod acts as the gas piston, but in the Saiga design, it does not.

[Cobra 76 two 2,677]

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