My TNW bolt broke.......

[junglewalk]

Two weeks ago, the internal sleeve of the front half broke in two places.........
The gun is too old for the warrantee to apply, so it is going to cost me $170. for the front half to be replaced.......I figure the gun has fired close to 5k rounds...
Anyone else having trouble with the bolt ???....jw

[MauserMatt]

Have you emailed TNW about it? Even if the warranty has expired they might still fix it for ya... It's worth a try anyway. Ya never know...

[junglewalk]

Yes, that is where I came up with the $170. cost for the front half to be replaced. It would cost $350. to replace the whole bolt........I sent it to TNW three weeks ago, and should get it back tomorrow......
FYI, what broke was the original german metal work of the two hook like end pieces of the front half, that inserts inside the rear half. .... Maybe next time, I should buy the fa bolt for $65. and use the front half after working it to the sa standard, buy copying the modifications of the original TNW sa front half.......That rear half of the TNW modified bolt with the interior guts, is where the big changes are that make it sa..........jw

[Intruder196]

Mine broke last year. You can see in the scan that one of the "ears" that retains the FP broke away and the other side was about to give way also. My warranty had already expired for almost a yeay.
But I fixed it by buying a FA bolt from IMA and then modified the front piece just like the TNW bolt.

[junglewalk]

:o Oh man Intruder, that is what happened to mine !!! ..So my thoughs are confirmed by you; Thank you, but I have been charged $187. for returning it to TNW, where as, I should have done what you did....... :P
Tell me Intruder, what were the modifications you did to the front part of the bolt to make it work...?.....thankyou....jw

[smoggle]

Why are they breaking like that? Is the spring tension too high? How about a picture of the body of the bolt?

[Intruder196]

Here is a scan of an unconverted bolt next to my TNW MG34 bolt. My TNW is on the right. You can clearly see the differences. I had to grind down the bolt body in order to fit the TNW modified FP retainer. You can see that they cut this part down and fitted it with a washer and c-clip.
To fix my broken bolt I merely removed the FA sear (not shown in this scan) and filled the slot with a bead of weld (like it looks on the broken TNW bolt.) Then I just ground down the back of the bolt body till the TNW parts fit and the gun fired like it should.

I think that when TNW grinds down this area it weakens the two tabs and they break easier. I also wonder if their FP spring might be factor as well since it appears to be really stout.
My breakage occured last Sept. And I have used the gun for at least two range trips firing at least 300 rounds each time and taken the gun to 5 reenactments and it seems to be holding up.
But since the breakage, it's one of the things I look out for each time I clean the gun.

[junglewalk]

Thankyou intruder 196 ..I printed your photo, and it is even clearer on paper. Magnificent, I appreciate you taking the time to photo and explain..... :arrow:
I assume you use the german blank barrel for re-enactments, and I figure it is less stress on the firing mech than shooting live.......thanks again......jw

[Intruder196]

I dont own a blank firing barrel. I use the cheaper drop-in forcing cone and it works fine with just that.

[smoggle]

Yeah that does look pretty weak. The Germans may not have built things heavy duty like the Russians butthey did engineer well.

[junglewalk]

Intruder, how large a hole is in this cone you mentioned, and do you use just crimped blanks, or do you use wood-tipped ones too.......
I have only used the two-piecer blank barrel with crimped blanks, or the hollow wood tipped blanks......This blank barrel, has rifling in the bore, and by the time the hollow wood tip comes out the muzzle, it is all burned & broken up, and if you do see anything at all, it looks like a speck here or there... :arrow: BTW, are you in the 196th Inf Regt?.....thanks....jw

[Intruder196]

The hole in my BFA is about 1/8. I used to use woodtip blanks but found that I get more muzzle flash with crimped rounds. Nothing tells the other side "hey you're getting shot at" better than good muzzle flash.
I reenact with 11thPZ out of Northern VA.

[Robert]

I was have this same problem.
What´s the cause of this bolt broke???
All parts in my bolt is german ww2 in very good condition and I´m using two-piece blank barrel with 4mm hole
Can anyone tell me what´s the cause of this?

[longhorn109]

I would say these are down to metal fatigue. Although Robert's firing pin retainer looks as if a hair line crack has given up.

Looking at the ammount of material that has been removed I cannot say that I am that surprised they failed. Looks like nearly 50% was removed. It was designed that size for a reason. Don't forget that not only are the spring forces being containing but also the forces created by the rapid acceleration and deceleration of the firing pin, spring and the retaning piece. They may not be heavy parts but when they are moving quickly that does not matter.

What is the reason for this bolt mod?

Another thing to remember is that genuine WW2 parts are 60+ years old and we don't know what has been done to them in all that time.

[smoggle]

The reason for the mod is the way it is made into a semi-auto gun. Since full autos are about $25,000 and there are few of them.

[longhorn109]

Sorry not making myself clear. I understand why it is modified (for SA reasons) I was curious what the mod does to make it a SA bolt. It would probably be clearer with the full bolt present. I don't know what the modifications are to make the MG34 SA.

[junglewalk]

The metal in our 'modified for semi' bolts failed next to the modified area, whereas Robert's failure occurred on the firing pin retainer!
This shows how strong the un-modified part of the bolt is, when left alone. ha!....
(I just paid 28k for a fa mg-34, found it on Gun-broker.com, yikes!!)

[junglewalk]

Opps, I should have addressed the mod/question also........The metal that is removed, is then replaced with a complete thick washer like ring & retainer. The semi-arrangement, has a 'mouse-trap' spring loaded trip level device installed right at that point, once completely assembled. ...
When the bolt has closed & locked with a round in the chamber, the firing pin is held back by this little spring loaded lever, and is released when tripped by pressure from the trigger group below. ...This lever that holds the firing pin back, has to have a solid steel face to lean against. It just so happens that one of the two openings of the unmodified bolt 'tunnel', is in the wrong place, when the bolt is locked foward, thereby giving this 'sa' lever no surface to brace and cock itself against.
Gosh I hope that makes sense;
This little spring loaded lever, is made by TNW, and is added to the rear part of the firing pin assembly.....

[Robert]

I understand that it´s 60year old, but I was broke 3 this parts last month

[Bil]

Robert-is yours full auto or semi? If you have broken 3 in the last month,I would think it is something other than this part being bad. ---bil