The MG34 Repair and Troubleshooting Thread

[FirearmsEnthusiast]

John at Marstar confirmed that the sear and sear ring kit they sell for $80 is “designed to work with the TNW MG34”. I ordered a set and will install on my spare bolt...

I agree with the comment in the post above that there needs to be a gap when the bolt head is aligned with the receiver track (ie. not rotated into battery) to provide the disconnect function. I checked mine today and there’s an approximately 0.5mm gap between the sear and sear ring when the bolt head is aligned as in when you are removing or installing in the receiver.

Hope this helps!

 

[DILLIGAF]

Thanks for all the info guys. Will give it a try. I ordered a bunch of new parts from TNW to finish my 2nd bolt. and I also broke down and ordered that 80$ kit from Marstar even if it looks like it was made with a dremel...lol...

 

[Deathrawt]

You might be able to salvage that sear if you grind a new edge on it and make it square again
I think tnw is using too soft a metal for the sear so it distorts too easily
Interesting that marstar has new sear and rings! I will have to check them out

 

[FirearmsEnthusiast]

Hey guys - quick update - the MG34 sear and ring arrived from Marstar today and I immediately took to the task of installing it on my spare MG34 bolt.

Here's the new sear ring in place (the parts don't include the c-clip to retain the sear ring, but I had mine from the original anyway). Part looks well made and look how nicely it fits into the assembly (you probably have to know what you're looking at to appreciate it!).





I then replaced the sear arm using the existing pin, spring, and sear arm retaining assembly. You can see both the old (shorter) and new (longer) sear arm.



I then rotated the bolt straight to #### it (nice 0.5mm gap between sear ring and sear in this position, as this is the "disconnector" function in the TNW design), then returned it to its "in battery" position (bolt head rotated). The new sear held very firmly with no play. Good interface between the sear and the sear ring. When I applied pressure on the back of the sear (farthest away from the bolt head), the firing pin tripped as expected. Recocking and repeating several times yielded the same result.



The ejector in this bolt is a bit long, so I'll have to file it down to fit it to my receiver to do the final "trigger testing", but it looks like the Marstar assembly will fit and work as advertised in the TNW MG34 modified semi-auto bolt.

 

[mg34]

would love to get my 34 back on the range but the govt says I cannot play with my fun toys.

 

[DILLIGAF]

Hey guys - quick update - the MG34 sear and ring arrived from Marstar today and I immediately took to the task of installing it on my spare MG34 bolt.

View attachment 197317

Looks a heck of alot better than the picture on the website. Mine will be here Wednesday hopefully it will fix my issue. I have 8 sear rings on the way with all the other parts to finish my 2nd semi bolt. so I can definitely part with one of them if you need a spare.

 

[FirearmsEnthusiast]

Looks a heck of alot better than the picture on the website. Mine will be here Wednesday hopefully it will fix my issue. I have 8 sear rings on the way with all the other parts to finish my 2nd semi bolt. so I can definitely part with one of them if you need a spare.

Agree that the sear ring I received looks a lot better than the listing on the Marstar website!

 

[1340]

spare MG34 bolt.

Is there any fitting to the gun (headspacing?) required when building a spare bolt?

 

[DILLIGAF]

Pulled this off the MG42 forum.

There isn't much written about MG34 headspace, I think because of the miracle of interchangeable parts, and:
-It's built into the dimensions machined into the barrel and bolt
-It can't change
-You can't adjust it
The MG34 f/a drops the firing pin latch at a point at which the bolt is still closing into the thread in the barrel. This point isn't precisely determined, but it doesn't matter either.
In the full/auto, I would say that if you strip out your bolt head and close it on a test dummy round in a barrel, the bolt head should engage "most of the threads". The rollers should probably "just" hit the stops on the barrel. Then you'll know you have "enough". Scientific? No......
In the semi-auto TNW system, if the bolt doesn't thread all the way into the barrel, the firing pin release is "shrouded" and it won't fire. I guess that's a safety feature if for some reason your headspace reduces on you.

 

[XRCD011]

This post will be a little off tangent regarding the ever fine craftsmanship of the TNW copies of the MG34........but being sorta MG34 related and this IS the MG34 thread here goes. Yesterday Sunday 12 Aug I took the schwimmer out to Embrun Ontario for the annual "Volksfest", with all the bad press and "ban guns" talk going on as of late I debated whether to leave the MG34 (dewat) at home but decided hell no, if anyone wants to debate my having a MG on a car at a car show then we can talk. So I get out there all set up having a grand time talking about the car and see a father and son of about 10 years old and he has the iPad going and taking a bazzillion pics of everything on the car and the guns. Now besides the MG34 there are a couple of stick grenades, a Stg44 and a PZ60 in the car for giving it that lived in and "loaded for bear" look. Anyways I get talking to the dad and he says his lad is over the moon seeing the schwimm. So at that I asked if (dad) know how to take a pic off the lads iPad, his son showed him how to take a picture . I then showed the boy how to climb aboard the car as there is a bit of a knack to doing so so you do not goose step into it. I get him in the passenger seat behind the MG34, put the seat up for him, uncradle the gun and have him hold it while dad takes a bunch of pics. The kid was grinning from ear to ear and absolutely beside himself he was in the car AND holding a MG...........AND has pics to prove it. The dad was cool taking pics and very much appreciated my allowing his son to sit inside. So that was my "good guy with a gun" deed of the day.

 

[DILLIGAF]

Got my package from a friend in the US today

time to get my 2nd bolt up and running.

 

[FirearmsEnthusiast]

Pulled this off the MG42 forum.

There isn't much written about MG34 headspace, I think because of the miracle of interchangeable parts, and:
-It's built into the dimensions machined into the barrel and bolt
-It can't change
-You can't adjust it
The MG34 f/a drops the firing pin latch at a point at which the bolt is still closing into the thread in the barrel. This point isn't precisely determined, but it doesn't matter either.
In the full/auto, I would say that if you strip out your bolt head and close it on a test dummy round in a barrel, the bolt head should engage "most of the threads". The rollers should probably "just" hit the stops on the barrel. Then you'll know you have "enough". Scientific? No......
In the semi-auto TNW system, if the bolt doesn't thread all the way into the barrel, the firing pin release is "shrouded" and it won't fire. I guess that's a safety feature if for some reason your headspace reduces on you.

That's my understanding as well. Headspace is a function of the chamber/barrel extension. Drop a live round into a barrel that is outside the gun and the cartridge sits just above the rim. As the bolt threads into the barrel extension, you basically get the headspace...haven't heard of any problems with this approach.

 

[DILLIGAF]

Well Im a super happy. The new parts from TNW solved my issue on my 1st bolt. The Sear and sear ring are a bit different then the original that came with the MG34. Must ben a Gen 2 ...lol

Now hopefully the Marstar parts can fix my other bolt.

Here is a closeup of the failed parts, Im not a machinist but shouldn't these parts be heat treated ? or made with something like S7 steel ?

 

[Wildey]

This post will be a little off tangent regarding the ever fine craftsmanship of the TNW copies of the MG34........but being sorta MG34 related and this IS the MG34 thread here goes. Yesterday Sunday 12 Aug I took the schwimmer out to Embrun Ontario for the annual "Volksfest", with all the bad press and "ban guns" talk going on as of late I debated whether to leave the MG34 (dewat) at home but decided hell no, if anyone wants to debate my having a MG on a car at a car show then we can talk. So I get out there all set up having a grand time talking about the car and see a father and son of about 10 years old and he has the iPad going and taking a bazzillion pics of everything on the car and the guns. Now besides the MG34 there are a couple of stick grenades, a Stg44 and a PZ60 in the car for giving it that lived in and "loaded for bear" look. Anyways I get talking to the dad and he says his lad is over the moon seeing the schwimm. So at that I asked if (dad) know how to take a pic off the lads iPad, his son showed him how to take a picture . I then showed the boy how to climb aboard the car as there is a bit of a knack to doing so so you do not goose step into it. I get him in the passenger seat behind the MG34, put the seat up for him, uncradle the gun and have him hold it while dad takes a bunch of pics. The kid was grinning from ear to ear and absolutely beside himself he was in the car AND holding a MG...........AND has pics to prove it. The dad was cool taking pics and very much appreciated my allowing his son to sit inside. So that was my "good guy with a gun" deed of the day.

Good story...sure made that kid's day!

 

[1340]

Here is a closeup of the failed parts, Im not a machinist but shouldn't these parts be heat treated ? or made with something like S7 steel ?

My sear ring looked exactly like that, two ridges around the edge with 2 low spots. The sear lever wouldn't engage the sear ring every time,so it stoned that edge of the sear ring a bit until the lever engages every time. The sear ring did seem to be hard. One thing I noticed, when I #### the bolt the sear lever engages the sear ring deeply. As the bolt rotates to the battery the lever loses a bit of engagement. I'll have to keep an eye on that.

 

[1340]

In the picture of your new parts, the sear ring does look hardened.

 

[Deathrawt]

Hopefully that fixes the issue, let us know how the marstar parts work and if they are better then the tnw ones

 

[DILLIGAF]

As the bolt rotates to the battery the lever loses a bit of engagement. I'll have to keep an eye on that.

Im currently looling to source heavier sear springs. That would also help the engagement.

Im also designing a new ring and sear stay tuned.

 

[FirearmsEnthusiast]

Well Im a super happy. The new parts from TNW solved my issue on my 1st bolt. The Sear and sear ring are a bit different then the original that came with the MG34. Must ben a Gen 2 ...lol

Now hopefully the Marstar parts can fix my other bolt.

Here is a closeup of the failed parts, Im not a machinist but shouldn't these parts be heat treated ? or made with something like S7 steel ?

Did you also swap out the firing pin spring to a German one, or do you need the heavier spring to shoot milsurp ammo? Also remember to check booster cone hole diameter...the gun will beat itself to death with a 9mm cone hole and hot milsurp ammo! I recall that you opened the hole up, so hopefully that and good lubication of the bolt and rollers and trigger bar rollers will help the gun run smoothly!

 

[DILLIGAF]

Well what's better than one MG34 bolt ? Two of course I did feel like BUBBA taking a perfectly good full auto bolt and bastardising it to conform to our stupid laws :-(