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Discussion Starter · #1 ·
7 should be a lucky number, but my 7th build has become a problem. I am building up an RPK 74 from a virgin Bulgarian barrel and Kvar trunnion. Even had Ted Marshall do the Molot shield. I have the barrel pressed in about 3/4 the way and it is now stuck. It has gotten beyond my comfort level. In frustration, while trying to push the barrel out I came down on the rear trunnion and moved it in a bit. So much for the nice rivet work and perfect receiver. This is quickly turning into a disaster.

Is there someone that you would recommend that can press the barrel back out?

Thanks a million.
 

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You can do it yourself... visual aids can be found here.
http://www.theakforum.net/phpBB2/viewto ... c&start=25

Get a piece of large diameter round stock that's longer than your receiver. Set up your build in the vice (see above link) with a nickle for a buffer to prevent deformation of the breech face. Get the pin as flush to the face of the surface of the breech as you can, get a good sized hammer and go to it. Remember to put something under your barrel assembly (like a bucket with a towel in it) to catch it when it comes free so you don't ding the muzzle on the floor.

So far as your rear trunnion, perfect rivets and etc.. just re-rivet it. It's not a race (at least I don't think it's a race) It's done when it's done but get it done right.

And measure your barrel to trunnion dimension.. it would appear your too tight. A little never sieze to lube the works never hurts either.
 

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Here is what you do, if its that stuck, some hammer trick is probably not going to work.

I hope you have a drill guide, if you dont, make one. Take a drill guide and drill the rear rivet heads out, just let the very tip of the drill bit penetrate into the receiver hole. Then take vise grips and pop the heads off of the rivets. You should then be able to cleanly remove and demill the rear trunnion.

Now, you will have access to pressing out the barrel. Use your barrel press tool with a long punch or whatever you have, make sure it is centered and BE CAREFUL, slowly start to push the barrel back out, and get it all the way out. You either need to get somebody to take a few thousands off of that barrel, or Freeze the barrel for at least overnight, preferrably about a whole day, and throw the receiver containg the front trunnion in the oven at about 200-250F. Lube the barrel and trunnion well and press it back in. Do it rather quickly, but be reasonable. This should allow you to get it in, hopefully leaving you enough time to headspace.

-Ryan
 

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Did you squash the rivets well enough? Maybe the barrel is colliding with the rivets inside the trunion if they're extending out of their little recesses they get squished into. Did'nt see any mention of that, so perhaps worth a thought?

They are virgin parts though, so you may have to "massage" one, or both.

If you do manage to get it out, the freeze method does just the trick sometimes. You might be able to get away with that?

Stay cool. don't get all frustrated! Take a time out and think. You'll get it.
 

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Oh, I was gonna ask.... Do you have a press? From the way your post read it sounded like it, but I could'nt quite tell.
 

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Discussion Starter · #6 ·
I do have a shop press. Thanks for all the advice! I too have come to the conclusion that I will need to remove the rear trunnion to obtain a better angle. One more attempt and I am going to find a professional. I am surprised at how well I have gotten this stuck

RSM
 

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Discussion Starter · #8 ·
I was simply trying to press it in. I got a bit exuberant with the press. I have learned a lesson. DO NOT force anything. I thought that the extra resistence was simply from them being virgin parts. It is frustrating. I had done really nice work on it up to that point. I have a lot invested to have it screwed up. Can only blame myself, and being to impatient.

Do you think that removing the rear trunnion would indeed give a better angle of attack?
 

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The odds are your ejector and/or center support is going to be in the way of a straight shot. If your going to disassemble rivets then disassemble the front and push the barrel back out with the press. If your not square up on the breech face with that pin... that's ok, that's what that nickle is for. FWIW... the 'hammer trick' has always worked for me, and I've has some barrels that were really stuck. If it doesn't seem to be moving, your not hitting the pin hard enough. Be patient. Get in a good position to hammer that pin. It should feel like a solid contact if your doing it right... and make sure your pin is on the upper, solid part of the barrel/breech face... not in or near the chamber.
 

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any chance you can heat it up with a set of torches?


sometimes an air hammer works wonders with the right attachment......let us know what the hell was holding it up !!!
 

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Discussion Starter · #11 ·
SUCCESS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I removed the rear trunnion. Using 5/8 inch round stock, the shop press, and some luck it gave loose.

I think that the dimensions are just a bit off. It had gone in about 3/4 the way and then seized. I was too aggressive with the press at that point. There is a gouge on the barrel at the 3 oclock position. It is maybe 1/10-1/5 mm deep and about 3mm wide and 5-6 mm long. It does not run the full length of what had been in the trunnion, but rather is only in the center of what was pressed in.

What now? Can I by hand open the trunnion up or take off from the barrel or do I need to have someone put the barrel in a lathe????????

thanks again,
RSM
 

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Even when the rear trunnion is removed, a 5/8" piece of round stock does not provide clearance for the ejector. Instead of removing the rear trunnion, it is much easier to use a tool like the one below. It has clearance for both the rear trunnion and ejector.
 

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I'd like to learn something more from rsm's misfortune so I don't end up having the same problem. When doing a press fit on an AK barrel & trunion, what kind of difference should there be between the barrel outside diameter and the trunion inside diameter?
 

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The right fixtures always makes a big difference. the key is holding the reciever and barrel,so they are balanced and so the press is applying the pressure equally balanced.

I have had good luck by cleaning the trunnion out and the barrel surface with 280-320 grit wetsand(sand with oil instead) paper. the slightest nick or bump, will cause nightmares. then I grease them with top notch bearing grease. I have had no problems so far.....
 

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I doubt a lathe is needed just yet, not sure.

Maybe the most likely cause of seizure was the relatively large gouge being created while pressing it in. I think whatever is producing the gouge must be dealt with first. And may be the only problem? maybe.



As far as sizing and the interference fit there is some variability from part to part even in the same factory. Barrels and trunnions are marked after manufacturing is completed, to quantify this variance in size from part to part. During assembly parts are chosen to go together that "match" more or less. With virgin parts in the OP's build this matching has not had a chance to take place.

We're just talking a few thousandths here but more than likely the issue is a trunnion that ran a little small and a barrel that ran a little large. Creating a match that would not have occurred in the factory. And a press fit that is excessive. This, of course, only if the gouge is not the only problem.

What should the press fit be? Beats me, but there is some variance here also. I don't use a press, at all, and my methods make it easy to tell how tight a barrel is during disassembly. With that and measuring crudely with calipers the press fit on my builds have varied from ~ .001 to .004 inches. Those super tight Romanian barrels are maybe 5 or 6.


To adjust the fit I use emery cloth and pb blaster. A long strip used in a shoe shine motion all around the barrel journal. Checking with calipers and test fitting as I go. I don't like struggling with the assembly so I adjust to the lighter side of press fit. I think it's a mistake to believe it must be super tight. The factory works faster with loose tolerances and machine force to compensate.


This is just my take on things, and would appreciate any input others have to offer.
 

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Discussion Starter · #16 ·
I used strips of sandpaper and a shoe polishing motion. When my cheapo gauge said that it was the same size as the trunnion I stopped. Pressed in with no problems. I still play the just too far out and just too far in game with the Go/ No Go gauges. Seems to be a ritual.

thanks again,
RSM
 

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Just for the record, I use a large 1/4" punch fixture that I made to press the barrels back out, it sits at a slight angle beause of the rear trunnion, but I have never had any problems.

Before that, I used the same punch and I just held it against the rear trunnion with my hand, while it pushed on the AKbuilder barrel press tool. The lateral force exerted on the punch is easily overcome by just hand pressure. You dont need any fancy tools :D

Use this technique at your own risk.
 

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This is my first AK build. I pressed the barrel in with my home made "Toth tool" and got it stuck a little off vertical for the rear sight, gas block, etc. about 3\4 in. I bent my press trying to take it back out, so I broke down and bought a real Toth Tool. Well, it bent too. Question: Should I heat the trunion and try again?
 

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When you say you bent your press, do you mean a hydraulic one or your self made toth tool? If just the toth tool, I would suggest getting a hydraulic press. I can’t say I’ve had any problems getting barrels out with the 12 ton I got. Unfortunate to need to invest in another tool when money is tight but it has been a must in my limited build experience. I haven’t had any experience with the 20 ton ones but I imagine those would be even nicer to have if you could afford it, but the 12 has easily been enough in my experience.
 
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