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Discussion Starter #1
I built a Yugo RPK a while back, and have been chasing demons ever since calling it complete.

It's current problem is cycling. After a round is chambered and fired, it will not cycle the action back enough to eject and load a new round. Most often, the empty shell remains in the chamber.


When cycled by hand, the action cycles almost as smoothly as any AK I've built, so I want to think that the bolt carrier is not binding on the receiver anywhere. The bolt appears to glide over the ejector without binding, and seems to pass over the hammer without any serious interference--at least no more than a typical AK rifle.


It seems as if the gas system is not working as it should, but after shining a light down the barrel, I can easily see that the gas port in the barrel and the gas block clearly line up, so I can only assume it is getting enough gas at the gas port.


It is using a US-made TAPCO gas piston. Have there been any problems with this type of piston being used? The gas piston does not appear to be binding in the gas tube, and the bolt carrier does not appear to be binding anywhere in the rear sight block.

Any ideas? I am at a loss on this one...
 

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if the rifle has fired how can the empty shell remain in the chamber? does the carrier remain closed or does the carrier open but fail to extract the round? have you cleaned the gas port?
 

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Discussion Starter #3
The bolt will move back maybe 1-2" before returning closed--not far enough to eject the round and chamber the next one. It's almost as if there is no gas blowing back the bolt carrier, or that the bolt carrier is somehow seizing in the receiver.

The gas port appears to be wide open, and the bolt carrier slides easily between the rails, so I don't know why it would not cycle when fired.
 

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Is the piston binding in the gas tube?

What type of ammo are you firing?

When cycled by hand does the round clear the chamber easily or is there excessive friction?

What does the chamber look like?
 

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I had this same problem with an SKS that was built out of parts. That gas tube was too big , I replaced it and it ran fine.

Your piston may be undersized or your gas tube may be a bit oversize. Try swapping the tube out and see what happens, though with the way the AK gas system is set up I'm guessing it's the piston. Hope this helps.
 

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Ok, don't take this the wrong way; but when you said appears to be clear does that mean you have put a gas port reamer down it or just visually inspected the gas port?

Also inspect the chamber see if it is pitted or anything or any kind of a build up of material is in the chamber.
 

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Discussion Starter #7
56type said:
I had this same problem with an SKS that was built out of parts. That gas tube was too big , I replaced it and it ran fine.

Your piston may be undersized or your gas tube may be a bit oversize. Try swapping the tube out and see what happens, though with the way the AK gas system is set up I'm guessing it's the piston. Hope this helps.

I replaced the stock piston with a US-made TAPCO piston. I had thought about swapping back to see if there's any difference, the only problem is the rifle would no longer be 922r compliant unless I can find some additional part to replace--it's currently using stock furniture, and US-made RPK furniture is a bit spendy for troubleshooting...


KMFDM said:
Ok, don't take this the wrong way; but when you said appears to be clear does that mean you have put a gas port reamer down it or just visually inspected the gas port?

Also inspect the chamber see if it is pitted or anything or any kind of a build up of material is in the chamber.

I can shine a bore light down the barrel and look through the gas port and clearly see into the bore through the gas port.
 

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I would swap pistons and try it. i doubt your door will get kicked in in the middle of the night for trouble shooting your rifle..
 

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I've seen a few of these with worn/corroded out gasblock's . i'd definatly swap back to the original piston [and run a pipe cleaner through the gasport] for a first step .
 

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Do you have a dial caliper handy ?? If so just check the outside diameter of the old gas piston against the tapco one and see if there is a difference. I'd also check the length as well. If it's too short it may vent all the gas really early in the cycle causing it to short stroke as your describing.
 

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Discussion Starter #11
56type said:
Do you have a dial caliper handy ?? If so just check the outside diameter of the old gas piston against the tapco one and see if there is a difference. I'd also check the length as well. If it's too short it may vent all the gas really early in the cycle causing it to short stroke as your describing.



The tapco piston is about 2mm longer than stock, and the OD is the same at the head of the piston.


The chamber is clean, but not shiny. After a round is fired, the action will not cycle back to eject the round, however I have no difficulty pulling back on the charging handle to clear the chamber.

I can't see any visible signs of the bolt carrier or piston seizing or rubbing against the gas piston or the rear sight block.

There is a fair amount of crap in the gas block, which I will do my best to clean out (my kit was in ROUGH condition when I got it) so we'll see if there are any differences.

Who knows.. maybe it'll be like a Century CETME and be a bitch for the first 200 rounds before finally loosening up and working like it should... :grin:


I really appreciate the replies so far, so thanks for all the suggestions. Hopefully this thing will get to working soon...
 

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i am having the same problem with a yugo rpk.i swapped barrels and i had a hard time getting the gas block off and on.i do not know if i deformed it or it was that way and i did not know it.i checked for all the causes like you did.finally came to piston and gas block.i found out with the gas tube off and bolt all the way foward the gas piston has side to side and up and down play.when i put that carrier into another yugo it fits snug like it is supposed to.i cannot find another gas block,so i am going to try to get a guy who makes gas pistons to make me one with a bigger head to fit the gas block.major bummer with this build.it is the only one that does not work.
 
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