AK gas piston question

[SSwee]

Is there a reason, purpose or benefit to the pistons offered with different number of grooves? Stock has 2, Tapco has 3, Red Star has 4. Is this nothing more than a way to ID the maker?
On changing out the piston, one I have that Perro changed and one stock that I need to do are not screwed tight into the carrier. They have a slight movement as they rock against the pin. I take this as normal. When I replace the stock one, do I just hand snug the piston into the carrier to drill the pin hole or is it screwed in snug and backed off slightly?
TIA
SS

[nalioth]

Different US makers mark their pistons differently. Tapco (http://www.tapco.com) marks theirs with "Tapco USA", midwestarmory.com (http://www.midwestarmory.com) has "Midwest USA" on theirs. Some manufacturers don't want to stamp anything, but use a different number of rings to differentiate theirs from Uncle Joes.

When you install a new gas piston, turn it tight and back it off half a turn. Mark your spot through the old rivet hole, unscrew and drill it. This will give you the play necessary for optimal function.

[SSwee]

Thanks.
Understood. Do the grooves serve a function in the operation of the weapon?
SS

[nalioth]

Yes, they work something like the piston rings in your automobile. I've noticed on Saiga rifles, there are no rings/grooves at all on the piston (cheap manufacturing principles).

[MID]

I think its more of a reliablity thing. The grooves give a place for any debris to go, instead of wedging between the piston and the cylinder.

[Perro]

you have a large amount of blowback on the piston - the rings serve no real purpose or function

it is supposed to be a loose fit - it should rock back and forth - that is a factory method

me personally, here is how i do mine
screw it into the carrier to hand tight, then back it off 90 degrees- 180 degrees (1/4 - 1/2 turn)
clamp it
use a high speed steel drill bit, and use the holes in your carrier as a guide for the drill bit. the high speed steel wont cut into the carrier - it will squeel like a pig but it wont cut the hard carrier
once you are half way through, flip the carrier over and drill it through on the other half

take your rivet and push it through the hole

smash it flat with your man hammer on both sides so it smashes the rivet into the taper on the carrier.

machine the rivet smooth to the carrier

done


and which one did i do for you?? I dont remember that?? curious



Mike

[SSwee]

What size drill? Just under the size hole in the carrier?

You didn't do it for me first hand. It's on a Romak I got from Fido that he said came from you. What receiver would you recommend for it?
SS

[Perro]

i use 1/8 inch rivets, and 1/8 inch drills

any receiver will work, but if you want the least amount of hassles, get a 100% receiver will all holes drilled - if i wanted my first build to go as smoothly as possible, id think about the nodak
i have built on alot of joeken, and alot of vulcan receivers without any problems though, they just take a fair bit more massaging to get them to work

[nalioth]

+1 on the Nodak Spud (http://www.nodakspud.com) receivers.

[M1 Tanker]

Sswee I've done them with the 3mm rivets from cope's and a 1/8 rivet from Perro, they both work just fine.

I also second the idea of using a 100% receiver for you first build. I didn't and it was a painful learning experience because you aren't really sure what your finished product should be.