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Posted: 10/2/2005 7:47:45 PM EDT
[Last Edit: 10/2/2005 7:59:18 PM EDT by Sauramen]
This is my second build.  First one went together well.  This one is not.

I am having trouble getting the bolt & bolt carrier (when put together) to go all the way forward.  Taking the bolt by itself, it goes along the rails nicely and rotates/locks.  The bolt carrier (thing with the handle that the bolt goes into) by itself goes along the rail nicely and snugs up to the front trunion.

If I put the bolt inside the carrier and insert it into the reciever everything is fine.  I slide the bolt carrier and bolt up and it rides nicely.  I watch the bolt piviot/lock (from the underside of the reciever) to the front trunion.  It is at this point that the bolt carrier stops it's forward motion.

Bolt and front trunion are the same serial number.  I have verified that the bolt is actually locking up with the trunion by both watching the bolt turn and marking the bolt position (and groove on the bolt underside as seen fron the bottom thru mag well) with and without bolt carrier.  

It seems that everything goes well up to the point that the bolt locks up.  It seems that at this point that the bolt carrier should proceed up a little bit more to snug up to the trunion.  It simply stops.  The bolt carrier can be forced to close using a piece of wood and a dead blow hammer.  It takes a few fair taps to get the bolt carrier to finish it's travel.  It take a few lighter taps on the bolt carrier lever to free it.

I have also tried the bolt and bolt carrier from another rifle.  The same thing happens.  Both parts run up and down easily by themselves.  When I put them together the bolt carrier stops it's travel after the bolt locks.

The "problem bolt and bolt carrier" seem to work correctly in my other AK.  The go forward, the bolt locks, and the bolt carrier continues forward and snugs up to the front trunion.

I would do some pictures but I don't know how to do that.  Is there a place to host the pic's?

P.S.  How do you get the trigger pin out of nthe bolt assembly?  I have a wood splinter in the rear end of the bolt right along the pin.  I need to remove the pin from the bolt to clear it.  Don't ask, it has been a really bad night.

Link Posted: 10/2/2005 7:50:35 PM EDT
Need more info.

What caliber?
What receiver?
What kit?
Are you having the problem with the gas tube installed?
Link Posted: 10/2/2005 8:05:33 PM EDT
[Last Edit: 10/2/2005 8:07:29 PM EDT by Sauramen]
It is a 7.62 x 39.  It was an old beater kit with an underfolder on it.  It may have been polish.  I really don't know.  The reciever is one that I bent myself using a jig.  Tapco nflats.  We have made 3 different recievers from the jig.  Each worked correctly.

The rails are an "E" drill bit index from the top.  We used the bits for spacing and to make sure the rails are parrellel.

I took my other AK outside to see if I could note any differences between the two and to see if the problem bolt and carrier would work in the working AK.  The only difference that I could not was that there was a slight bit of a gap between the reciever and the trunion on the left side as looking from the butt stock.  

I removed the gas piston because there was a slight bit of interferance with the piston.  I have the problem with no gas tube or pistion on the bolt carrier.

Link Posted: 10/3/2005 12:57:09 AM EDT
Link Posted: 10/3/2005 5:07:11 AM EDT
I had a similar problem with a Romy. I found a small protrusion on the bolt (about the size of a grain of rice) which showed some wear marks, and after I filed it smooth the action worked flawlessly. I can only guess that the original receiver lined up the bolt, carrier and trunnion slightly differently.
Link Posted: 10/3/2005 6:06:18 AM EDT
[Last Edit: 10/3/2005 6:10:32 AM EDT by Quarterbore]
I would suggest taking a black marker and mark the surface of all the rails (upper and lower) as well as the ejector.  Then slide the bolt/carrier forward and STOP when it gets stuck and pull it back again.  Look for any marks that indicate binding.  

If your lower rail is not linned up with your trunion that can also cause problems...  When I did my AMD-65 build I ended up using a "G" sized drill bit to get the lower rails lined up with the rails that are built into the trunion.  Parallel is important but so is the distance from the top and the alignment of the lower rail to the rail built into the front trunion, so check if these are lined up with each other.  If it is a minor contact, you can bend the lower rail a little (I needed to give my lowerrail a little tweek on the lower rear side of my last build)

If the front trunion is in the receiver crocked, I would start over and pull the barrel and front trunion as opposed to cutting on the trunion or bolt myself...  Hopefully there is another explanation.  Minor burs on a bolt is one thing but remember those little lugs are what keeps the gas in the barrel as opposed to your face  

Good Luck!

Link Posted: 10/3/2005 6:46:36 AM EDT
I had the same issues (almost) with a couple '74 builds.  Seems the gas tube wasn't fully seated downwards and the BC would bind.  I had to wiggle the gas tube around a little and it would clunk into place a little lower in the RSB.  Then everything was OK.

I agree with QB about the spacing.  I use whatever maximum rail spacing keeps the rail holes in line and takes up the slack, allowing little if any pivoting on the pins.

Difficult to tell without acutally seeing and touching.....
Link Posted: 10/3/2005 11:10:38 AM EDT
Thanks for all the help and suggestions.  I will look and see if any apply.

Can someone tell me how to pull the firing pin from the bolt?  I need to clear the wood splinter from it.


Link Posted: 10/3/2005 12:03:28 PM EDT
there are two pins in the bolt. the little one hold in the fireing pin, you can punch it out with the little tool that comes in the AK cleaning kit.  The little pin also holds in the big pin which holds in the extractor.

I had some binding issues on some home built receivers. on was because the trunion was installed canted downwards. The other was because the rails were not in the correct possition relative tot he trunion. on one of them, I ground a little off some non critical areas of the trunion, the bolt carrier was binding on the left top of the trunion, I just shaved a tiny amount there, and it works great now.

I have never had this problem on a factory built receiver. mostly it has to do with home built receiver rails being to low or to high. But a canted trunion will also cause binding, as the piston reaches the gasblock, any bit of cant will be magnified.
Link Posted: 10/3/2005 12:07:48 PM EDT
There is a cross pin holding the firing pin in place. 2mm, I believe. They have to be driven out with a hammer and punch. They can be very tight. Take care to put the firing pin back into the bolt the correct way. One side has a little longer cut on it. This side needs o be on the cross pin side.

Link Posted: 10/3/2005 3:16:18 PM EDT
[Last Edit: 10/3/2005 3:20:20 PM EDT by Sauramen]
I descided to remove all the parts from the old reciever and bend up a new one.  I want to make sure that I have the correct order for rail alignment.

Bend up and heat treat the reciever and heat treat the rail.

Grind down the front part of the rail so that the front trunion slides into place and their is no gap between the inside of the reciever and the outside of the trunion.

Insert the trunion into the front of the reciever.

Take the rails and use a drill bit (index bit) to make sure the rails are parrellel to the top rail AND that the correct spacing is achieved to have the top edge of the bottom rail line up with the top of the rail guide in the trunion.

Attach rails in your favorite method.  For me that is spot welding.

Before, the rails were set up using the existing pre-drilled holes.  It was an "E" drill bit.  I remember that the bolt was tight going down the rails.  This time I have the rails lined up with the trunion and it is an "H" drill bit.  That is quite a bit of difference going from E to H.  The holes for the rail don't line up right now but that is easy.  

If it is that I need a larger spager ("H" instead of "E")between the top and bottom rails, that could account for the bolt carrier binding at the end of it's travel?

I also noted an ever so slight downward cant to the barrel in relation to the reciever.  I would not have noticed it if I had not really been looking for it.  Does anyone have any ideas how that might happen or what I might do to prevent it in the future?


Link Posted: 10/3/2005 3:19:13 PM EDT
I think the one I just built I used a K or H bit for.  Whatever the largest bit I could put in there and still have the hammer pin and crossmember pin in.  Lined up perfectly.

An E bit seems very small...still this might not be the problem
Link Posted: 10/5/2005 8:06:54 PM EDT

I think I understand what is happening.

I started building up a completley differnt kit.  I bent up the reciever and fitted up the front trunion.  I then line up the rails to the trunion rails using something like an "H" drill bit.  Just the one to match the rails up.  I had to drill out the hole in the reciever a little bit because it was not quite lined up right when the reciever/trunion rails were matched for space.  I spot welded the rails in.  I then put all the rivets into the front trunion with tape to locate the trunion (except 1 on the left side middle-It would not line up and needed to be hogged out a bit).  I filed everything so that the bolt and trunion ran all the way back and forth freely together.  I then riveted the trunion in place.  I tested the fit and everything ran correctly.  I then put the barrel in the trunion.  After that, I had the same problem of the bolt carrier not finishing it's travel after the bolt locks.

I looked, adjusted, filed, ad nosium.  Still no luck.  

In frustration, I hit the bolt carrier/bolt on top of the bolt carrier while it was driven all the way forward in the reciever with my dead blow hammer .  I did not have the trigger guard in yet so and barrel was mostly flat with the reciever .  (In actuality, the barrel was resting on a lug and the reciever was resting on it's rear edge).  The bolt carrier jumped back.  Before, I had to drive it back &/or forth with a dead blow hammer.  I picked the unit up and tried the bolt carrier.  It was free except for just a little at the end.  Much closer to the bolt carrier being fully closed than before.  I figured, what the heck and whacked it several more times.  The bolt now seems to run completley free.

My conclusion is that systematically, I am getting the barrel just a few degrees sloping down.  I am not sure how this is happening.  Any ideas?  Could it be the flats (Tapco)?  Could it be the jig?  How do you ensure that the front trunion is placed where it needs to be?

I know how to fix the problem when it happens, but I would like to figure out how to correct the system problem.


Link Posted: 10/10/2005 4:50:45 AM EDT
I had a problem like the one you explained in your post. I found out, that i had pushed the barrel in about 1/16 and pinned it. That small amount of diffrence made it do exactly as you described. I think the barrel was actual canted about a 1/8" to the right and the combination of the two caused me HUGE problems. The rifle came out great but didnt function and after a week or two of just concidering it to be a wall hanger. I pressed the barrel out again and gave a second shot. Worked excellent. Everything is smooth and good to go now.
Link Posted: 10/10/2005 11:47:15 AM EDT
I had a somewhat similar problem as you described here, the problem was that when I attached the front trunnion, I bent the upper rails up just a bit, and beating the down solved all my problems.  It seems when I smashed the receiver in a vice to compress it against the trunnion that it caused a little bit of bowing at the top where the receiver enters the trunnion. This caused the rails to bend ever so slightly, but a few whacks with a hammer and all was fine. A good use of Percussive Maintenance, if I do say so myself.
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