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MG34 Wont cycle

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MG34 Wont cycle

Postby sdasal » Thu Aug 01, 2013 4:53 am

Hi, I've done quite a bit of reading on the site so far and haven't really found a thread going over a MG34 that won't cycle, most having feeding/ejection issues, mine is effectively a reliably feeding bolt action.

Its a re-weld receiver, the bolt slides smoothly through it no hang ups or even rough spots, you can just tilt the receiver disassembled and the bolt will slide from end to end. The gun has the smaller 9mm booster cone in it, new recuperator spring and mainspring. It will feed rounds manually all day long, and you can cycle a whole belt through it bolt action without a single failure to feed, extract, or eject. The barrel slides freely in the jacket, and into the front of the receiver, manually cycling is smooth and the bolt unlocks easily when the charging handle is used.

My question is how to adjust/setup the booster assembly, I've found bits and pieces of the original translated manuals and it mentions adjusting the booster assembly for weak cycling guns, does it mean outwards or inwards? is there a base setting that should be set on it? I've sat there and played with it in and out and have had some adjustment show to where the barrel recoils more and is starting to unlock the gun but not fully. Is there any spec as to the gap around the outside of the barrel in the bearing area behind the booster cone? I'm new to the MG34 platform, I've owned the kit for 6-7 years now and just finally got around to building it.

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Re: MG34 Wont cycle

Postby 42rocker » Thu Aug 01, 2013 6:38 am

sdasal
Welcome to the site there are several mg34 folks on the site that I'm sure will we around to help you out. My mg34 parts kits are like yours used to be, sitting around waiting to be built. Good Luck.

Later 42rocker

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Re: MG34 Wont cycle

Postby jbaum » Thu Aug 01, 2013 1:28 pm

So, is this built as a semi or full auto?
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Re: MG34 Wont cycle

Postby sdasal » Thu Aug 01, 2013 4:30 pm

I Guess I should have clarified I work as a gunsmith for an 01/07 FFL and its built as an MG. I've never really had any problems with any other builds we have done here but this one I'm not really sure where to start, as far as I can tell everything is functioning perfectly, the receiver is straight and fits all the proper dimensions, the bolt slides very smoothly the cams look good, the springs are new, the bolt is cleaned an oiled etc. The only thing I'm not familiar with is the proper setting for the booster cone.

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Re: MG34 Wont cycle

Postby jbaum » Thu Aug 01, 2013 5:06 pm

The locked barrel/bolt have to move rearward to unlock the bolt so that the bolt can continue rearward. The recuperator pushes the barrel again forward so that it is in the proper position for the bolt to lock up with it again.

I'd check the recuperator to make sure it isn't binding and not letting the barrel travel to the rear.

According to the manual, the nozzle size should be 11mm. Once you get the gun working, put the right size nozzle in it. You want to use the largest nozzle you can and still have the gun work, otherwise it beats the gun unnecessarily.
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Re: MG34 Wont cycle

Postby sdasal » Thu Aug 01, 2013 5:19 pm

I have checked the recuperator and its fine, the barrel with the booster off will slide easily when pushed on from the muzzle. I was just curious because in some of the older manuals it said to adjust the flash hider cone a certain number of "clicks" to make the gun cycle harder if its cycling weakly or not firing semi auto when the top trigger is pulled.

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Re: MG34 Wont cycle

Postby haak48 » Thu Aug 01, 2013 6:21 pm

The correct booster cone size is 11mm (.445"). The booster is meant to be tightened completely. Also, a common cause for firing single shots only is the feed block insert installed for a right hand feed. Be sure it is correctly set up to feed the belt from the left. The gun was designed to allow feed from either side and it is not uncommon for this to error to occur. The gun will become a "single shot" because the feed pawls will operate in the wrong direction. Good luck. JH

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Re: MG34 Wont cycle

Postby sdasal » Thu Aug 01, 2013 6:57 pm

I have the left hand feed only tray meant to use the drums, so that isn't an issue. I guess I'll just have to keep messing with it.

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Re: MG34 Wont cycle

Postby jbaum » Thu Aug 01, 2013 7:40 pm

The barrel should not push in easily. It should have enough strength to support the weight of the gun and bounce quickly out if pushed on hard.

sdasal wrote:I was just curious because in some of the older manuals it said to adjust the flash hider cone a certain number of "clicks" to make the gun cycle harder if its cycling weakly or not firing semi auto when the top trigger is pulled.


I've translated every German manual for the MG34 that I can find (9 of them), and I don't remember any of them saying that the recoil booster was adjustable. What manual is that in? If it's the US manual, disregard whatever is in there as it's a big piece of crap. Same goes for their manual for the MG42. People who didn't understand how the guns worked wrote the manuals for foreign guns. They still do.

Boosters on both guns are screwed on tight, and only backed off far enough to get the lock to go into a groove.
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Re: MG34 Wont cycle

Postby sdasal » Thu Aug 01, 2013 7:42 pm


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Re: MG34 Wont cycle

Postby jbaum » Thu Aug 01, 2013 7:45 pm

See the above comment about US manuals for the MG34 and 42. If that's your source of information about this gun, you're in deep doo-doo.

Also, check the bolt catch for function. If the bolt isn't extracting and ejecting the empty shell, it's because the bolt isn't releasing from the rear of the barrel. Does the bolt head rotate and disengage the barrel when you push the barrel fully in? It should.
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Re: MG34 Wont cycle

Postby sdasal » Thu Aug 01, 2013 7:51 pm

yeah I figured that out now, alrighty well I guess back to the drawing board on this thing, I'll continue to polish the rails and mabye the cam area hoping to get this thing to work. right now I've tried original WW2 german ammo, yugo suprlus, and PPU commercial ammo....

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Re: MG34 Wont cycle

Postby jbaum » Thu Aug 01, 2013 8:05 pm

Do NOT use 65 year old ammo in a 34 or 42. A 1/25th of a second hang fire (common with old ammo) means an out of battery explosion. You wouldn't buy a $30,000 car and get gas from the junk yard, would you? I have pictures of blown up guns, and I had a friend who wouldn't listen when I told him he was going to blow up his 42. I picked the brass shreds out of his forearm with a tweezers after I stopped laughing at him. It wasn't pretty afterward, but the barrel change door just took a deadblow hammer and a block of wood to make it straight again.

Also, old steel cased ammo corrodes from the inside out. Looks fine till it tears a shell head off and stacks the next round in on top of it. It's even more prone to blow the gun than the old brass shells.

You can polish the rails till you see yourself in the reflection. That's not the problem.
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Re: MG34 Wont cycle

Postby 42rocker » Fri Aug 02, 2013 7:56 am

One of the things that I've learned to do on this website is to listen to John about this type of stuff. If you are running full auto then really listen to him about the ammo. Yes you can get away with using old ammo "most of the time". It's that one time that you have to rebuild after that's the problem.

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Re: MG34 Wont cycle

Postby haak48 » Fri Aug 02, 2013 11:32 am

sdasal wrote:I have the left hand feed only tray meant to use the drums, so that isn't an issue. I guess I'll just have to keep messing with it.

It is not the feed tray, it is the pawl insert in the feed block in the top cover. Make sure it is set up for left hand feed and matches your feed tray. JH

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Re: MG34 Wont cycle

Postby sdasal » Fri Aug 02, 2013 1:11 pm

as for the ammo issue, I only had shot 3 rounds out of a starter tab of the old german ammo, I hadn't planned on using it but mainly wanted to see if it made a difference, I had a belt that was original ammo linked up for display and grabbed just the starter tab off of it. Thanks for the warning though, the bulk of my ammo is yugo surplus as I had a source for the 900 round crates for $52.99 per crate awhile back....

As for the feed block, Its setup the right direction as well, like I said I have no feed/fire/extraction/ejection issues. The gun goes feeds, goes bang, and extracts and ejects every round that I manually cycle through it.

The booster cone is 9.5mm trying to get some extra power in the cycling, the recuperator and barrel recoil very freely when pushed on by hand. I cannot however get the bolt to unlock using this method, I'm not sure if thats normal or not, the bolt unlocks easily and smoothly when using the charging handle, the barrel recoils with the bolt, it unlocks and will retract no problems, but if i leave the bolt in the locked position, booster off and try to cock the bolt by pushing the barrel rearwards i can only get it to cam about half of the way unlocked. Whether or not this is normal I'm not sure, I had assumed it was since I doubt my thumb pushing on the muzzle could equal the forces of recoil that would normally be pushing it rearwards.

The only other thing I noticed is that the barrel is not terribly tight in the bearing area behind the booster, the front of the barrel has the grooves which should be gas check rings right? if the front of the barrel is too loose would that cause cycling issues? Its not super loose, but could be a few thousandths larger if it did need to be to get a good seal...

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Re: MG34 Wont cycle

Postby jbaum » Fri Aug 02, 2013 2:46 pm

I guess maybe the easiest thing to do will be to find another working MG34, and compare between the two.

Diagnosis online is pretty tough. We had a guy with a malfunctioning MG42 that took us weeks. He finally posted a video of it screwing up, and I saw that his ejection port cover was flopping around, causing the extracted shell to not eject properly.

It could be something simple (it usually is), and that's what makes it hard to figure out without being there and seeing it.
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Re: MG34 Wont cycle

Postby sdasal » Sat Aug 03, 2013 12:15 am

I'll try to get some video, its hard because I only get to shoot into the bullet trap at work for now, I only try it with starter tabs and in semi so far. I am a gunsmith and have built MANY different kinds of guns everything from stens, all the way up to PKM/M60/M249 for us and myself, but this is my first MG34, and I thought I had it right, but I guess not, I just figured I'd come here to see mainly about the booster adjustment, but I guess that was bad info from the US manual.

I'm gonna take a few pics of the gun when I get a chance which wont be till monday when I can get it out of the safe at work, but honestly there probably isn't much to see wrong with it. i'm gonna take the bolt apart and give it a good cleaning and lube, the only other thing I haven't messed with is the firing pin spring, I have had the rear part of the firing pin screwed all the way down and then locked, would backing that out one rotation possibly help?

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Re: MG34 Wont cycle

Postby anjongni » Sat Aug 03, 2013 4:52 pm

I'm don't have a f/a MG34, but it's a good discussion, soooo...As the bolt recoils to the rear, it (1) extracts the empty (2) ejects it, (3) the cartridge stripper passes under the new round, (4) the sear holds the bolt or the disconnector releases it.....Is the bolt cycling to the rear somewhat, just not far enough to a) latch onto the sear in Einfuer, or b) not strip off a fresh round for some reason? Can you determine at which point it "stalls"? Perhaps a short belt of new, fresh ammunition would provide more clues...Phil

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Re: MG34 Wont cycle

Postby sdasal » Sun Aug 04, 2013 11:29 am

It never even makes it to fully unlock. basically I rack the bolt, it locks rearward on the sear I pull the trigger, it feeds goes bang and then stops there. the barrel does recoil some but not enough for the bolt to cam open, its effectively a belt fed bolt action at this point.

This is what worries me, the bolt is smooth in the receiver, the barrel slides freely against the recuperator and in the jacket. I can push the barrel back far enough to almost get the bolt to unlock by hand but can't quite muster enough force with my thumb pressing on the muzzle. I do happen to have another recuperator rod that seems a bit shorter than the one that is in the gun though, I'm thinking of trying to replace that and see where that gets me, I just noticed it yesterday when opening the barrel jacket, this rod actually sticks slightly past the front of the receiver when the jacket is open where as the older one i had in it before was flush....i doubt its too long and stopping the barrel early but thats my only thing so far.


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