Problem with M-70AB...Yugo AK--HELP!

[SteelCore]

Hi, all:

H E L P !
Hey, took the M-70AB Underfolder to the range this weekend, put about 60 rounds thru it, and noted that the receiver had a lotta motion in it relative to the bbl and trunnion, I could slide it a few mm back and forth...

I took the rifle apart, and found the issue: bad (as in loosened) rivets thru the trunnion on either side of it... seems the rivets weren't properly peened, the builder must've taken a shortcut and tack welded them in place from the outside of the receiver...you can see on the outside of the receiver where the rivets have broken loose from the receiver. (I'm talking about the rivets on either side of the magwell, the leftmost rivet show in the pic below)

So, I need a fix. I've peened rivets before, so my questions are these:

Are the only two rivets that hold the receiver to the trunnion? I can see the heads of them in the inside of the rifle, going thru the trunnion and out the sides of the receiver.

Can I obtain these rivets easily?

Is there anything else I might be missing?

I'm the third owner of this rifle, so I don't think I could send it back to the build company to have it fixed. I really like it tho, and don't wanna dump it if I can fix it by replacing two rivets.

BTW, this thing outshot the WASR 10 all day at the range, even before I noted the thing was coming apart!

---ETA---
This is the ame type of receiver I have, the DC Industries one...
http://pictures.auctionarms.com/297590/f215a8b3272f6b4207a410ef4926dd98.jpg

Now the way my rivets differ from these (and the ones in my WASR10) is that on my M-70AB2, they appear to be sheard off, or ground off, so there are No rounded rivet heads on the one I have. This kinda worries me.

[nalioth]

All 5 rivets hold the trunnion on. Since the middle one is a long rivet, and goes ALL the way through the trunnion, i don't think it's gonna come apart soon. . .

BTW, TAKE PICTURES and show us.

[SteelCore]

so you're saying I should just fire it, even tho it feels like it's gonna come apart? I'd at least like to fix the loewr ones that are working themselves out...seems dangerous or sloppy to me, correct me if I'm wrong. I mean, the WASR I have has a tight and solid fit between receivr and trunnion...

ANother issue:

The button that releases the button for the topcover worked fin until afer I shot the rifle....then I couldn't push that button in to release the topcover button...I unscrewed the button assembly, and I could see that in the block of metal back there where the reciol spring fits in, that the holes in the receiver and in that part were no misaligned. If I leave that button out, everything seems to work OK.


I will try to get the digi cam up and running and take PIX.

[Otis61]

I don't think its that hard to replace the rivets. I know I hate using tools that are sloppy.

[nalioth]

so you're saying I should just fire it, even tho it feels like it's gonna come apart? I'd at least like to fix the loewr ones that are working themselves out...seems dangerous or sloppy to me, correct me if I'm wrong. I mean, the WASR I have has a tight and solid fit between receivr and trunnion...

ANother issue:

The button that releases the button for the topcover worked fin until afer I shot the rifle....then I couldn't push that button in to release the topcover button...I unscrewed the button assembly, and I could see that in the block of metal back there where the reciol spring fits in, that the holes in the receiver and in that part were no misaligned. If I leave that button out, everything seems to work OK.


I will try to get the digi cam up and running and take PIX. The rivets should probably be looked at by someone with the knowledge of AKs. The rivets visible in the mag well are easy to fix.

The button for the recoil spring/top cover is a :king: :queen: PITA

So much so, I think i'm gonna build all my Yugo fixed stock rifles with Yugo RPK receivers (no push button hole in those)

[SteelCore]

Yeah, I'll prolly just leave the button release for the top cover off, since it doesn't afect it at all.

The one thing about the looseness of the receiver-to-ttrunnion fit that bothrs me is that it seems like it could cause a misalignment of the gas tube and the piston, since the piston is receiver-based in linearity, and the gas tube is based on the bbl and trunnion...so if they're off by a few degrees because they don't align right, that worries me.

[nalioth]

Yeah, I'll prolly just leave the button release for the top cover off, since it doesn't afect it at all.

The one thing about the looseness of the receiver-to-ttrunnion fit that bothrs me is that it seems like it could cause a misalignment of the gas tube and the piston, since the piston is receiver-based in linearity, and the gas tube is based on the bbl and trunnion...so if they're off by a few degrees because they don't align right, that worries me.
If it's that loose, I'd find a build party or someone in your area with the knowledge and / or tools and get some real rivets put in it...

[SteelCore]

That's what I'm gonna have to do. I have a PM out to Rahatlakhoom since he's within driving distance...

I think I'll order the rivets now, and ohopfully he can help me out or give me access to his press...

K98 helped me out on the phone with options and dignosis too.

[Grasshopper]

Thank the Gods your all in one piece. I'm glad you found this problem before you got hurt.

[SteelCore]

It coulda been close, after talking to K98...glad I noticed it after 2 mags.

[Rampager]

Keep in mind too that bolt locks into the trunion and that's where the vast majority of the forces are at play. But yeah it's best to get it fixed though.

[texlurch]

On the button, you can usually just dremel the receiver out to match the button hole in the rear trunnion, and it will work fine.

[SteelCore]

Weird thing is that before firing, It lined up. I think the cheared/spot welded rivets might've moved a bit....scary...

[bullseye]

Watch it moving around, you could eventually shear a rivet with it being loose then it could get bad in a hurry. At least you are responsible enough to want to fix it, I know some that would shoot it till it fell apart. :(

[esninak]

did any one else notice that that isnt a bulged yugo reciever? whats going on there? they must have switched out the trunions to fit a standard one. who built your gun? mine is a century M70AB2 that was built by DC, but the lettering is on the side of the reciever, not the bottom by the magwell like yours. mine is tight and shoots great. maybe you got a fake yugo there.

[nalioth]

did any one else notice that that isnt a bulged yugo reciever? whats going on there? they must have switched out the trunions to fit a standard one. who built your gun? mine is a century M70AB2 that was built by DC, but the lettering is on the side of the reciever, not the bottom by the magwell like yours. mine is tight and shoots great. maybe you got a fake yugo there.

Some Yugos came from the factory with non-bulged trunnions. I have a kit with a non bulged trunnion.

Century receivers built by Nodak have the information on the side.
Regular receivers built by Nodak have it on the bottom.

BTW, that's not even his gun in the picture. HE STILL HASN'T POSTED PIX!!!

[esninak]

ok, learn somethin every day, thanks for stratening me out nolioth.

[Seattlefungus]

Steelcore, just for future reference, check out http://www.ak-builder.com/ak/modules.php?name=Content&pa=showpage&pid=21 for Yugo rivets. IMHO, he's got the best. US made and designed for the Yugo and treated with Black Oxide... Full set is under ten bucks and work perfectly. He's got the long swell neck rivets for the oversize Yugo trunion and the short ones for the pistol grip/selector plate plate, all in one nice package...

[Hoot]

You're not going to believe this.

I was the person who bought that Yugo underfolder as new from an auction and was selling it to Keith.

Well, I got it back and was performing a postmortem on it. Of the four trunnion rivets and barrel pin, one rivet had failed in what appeared to be the middle of the rivet head in a way I've never seen a rivet fail. Like it's shaft had parted from the rest of the head concentrically. What I couldn't understand was why, with just one rivet failing, was the trunnion moving around so much in the receiver. Surely the other three rivets and barrel pin, which showed no signs of head distress, were not that small compared to the holes they went through, to allow so much slop?

They weren't, since they were never drilled. Upon carefully grinding the distressed head and punching out the remainder of the rivet, the trunnion, with the barrel in it fell out of the receiver. inspection revealed that whoever built this gun merely sanded off the rivet stubs and barrel pin flush with the trunnion face, carefully slid it into the new (undrilled) receiver and spot welded through the receiver on top of those ground off rivets and barrel pin. He then spotted a small puddle of welding material over where the rivet heads should have been to look like them. Darndest thing I've ever seen. Despite being a shoddy approach to doing it right, it was done by someone skilled in both spot welding as well as MIG or TIG welding.

Problem is now, what I have is a jizzed up Yugo UF kit. I can drive out the barrel pin and one of the other three rivets without much trouble, use the spot weld marks to drill for new rivets and a barrel pin, but I can't get the other pair of rivets out without pressing out the barrel and I really didn't want to have to do that. Besides, I don't know what effect spot welding and puddling the false heads had upon the hardness of the receiver. The other receiver rivets and the rails look like the were done right. It is tempting to consider only replacing the barrel pin and one pair of rivets and run with just those four connection points as opposed to six connections points. I'm certain that is not good for the reliability of the trunnion to receiver mount.

I am not anal about design purity and have a sizable number of hardened, black parkerized, button head cap screws at my disposal. I may drill out and tap all six points and just retain the trunnion with screws and locktite.

What a weird one... :icon_neutral:

Hoot

[texlurch]

Screw builds will work fine, just don't drill into the barrel. You could replace the long front rivet, and the two by the magwell, and then just run a pair of screws on the uppers...

Shouldn't have to replace the barrel pin, it is pressed in.

*edit* upon re-reading this, I think what you are calling the barrel pin is the long rivet on the front of the receiver, below the barrel?

I would say knock out the barrel and redo with rivets, but that is just me.

[nalioth]

Hoot, from what you've found out, you could go one step up and use . . .


U-DRIVES :eek::bull::hammered::nar:http://www.novarata.net/forum/images/smiles/devil.gif:icon_cry::drink::hammer::roflmao:http://www.novarata.net/forum/images/smiles/devil.gif

All sick joking aside, Hoot, do you know who originally built it, so we can watch out for him?

[Hoot]

More from observation.

I was mistaken, the trunnion was not spot welded, the receiver did indeed have the holes drilled in it. Whoever assembled it welded through the holes onto the original rivet shanks, then puddled the weld material to look like rivet heads. The rear trunnion and trigger guard are done the same way, though for the moment, they seem to be faring better than the barrel trunnion. Also, not being an AK builder, I misspoke about the barrel pin. I mistook the one barrel trunnion rivet (long one) as the barrel pin. The receiver is going to be a challenge. I need to grind down the weld puddles and reopen the holes. No telling the effect the heat from welding had upon the metal around the holes. Perhaps a new receiver would be the way to go. I can get them from DCI right here in town.

more as I go...

Hoot

[nalioth]

Hoot, i'd not worry about the heat treat around the trunnion holes. Once you get new rivets in, they're not gonna go anywhere. It's the heat treat on the guide rails and center section of the receiver you're concerned with.

[k98k792]

I would go with a new receiver.

[walt-oxie1]

Hoot, i'd not worry about the heat treat around the trunnion holes. Once you get new rivets in, they're not gonna go anywhere. It's the heat treat on the guide rails and center section of the receiver you're concerned with.

I agree, People build on flats/blanks all the time without the trunnion areas hardened. Since the receiver has been welded and the metal temper has changed I would heat treat the rivet holes after they are drilled. Just like you would do on the trigger/hammer pin holes on a flat/blank build.

[Hoot]

Thanks guys. Looking at the inside of the receiver, where it wasn't painted, the heat discoloration did not radiate out very far from the holes, so I'm not concerned about the rails having detempered.

My Mom's health has taken a serious turn and I'll be flying out to Maryland Thursday morning, so I probably won't be doing much with it for a week or so.

More when I do...

Hoot

[walt-oxie1]

Thanks guys. Looking at the inside of the receiver, where it wasn't painted, the heat discoloration did not radiate out very far from the holes, so I'm not concerned about the rails having detempered.

My Mom's health has taken a serious turn and I'll be flying out to Maryland Thursday morning, so I probably won't be doing much with it for a week or so.

More when I do...

Hoot


My thoughts and prayers are with your mom, you and your family. I hope all is well.