ANOTHER bolt gap question <grrrr>

[clutchdust]

OK folks, I'm new but I've been doing some reading on this whole thing and I have problems. After reading what I can find on bolt gap, I don't have enough (as in, I don't have any). The other thing that I found on mine after reading is that my charging handle has no slack in it either when the bolt locks in the battery.
As you may have figured, this is a Century CETME, but I didn't buy it from them. Same story, different gun, impulse buy and I didn't do my homework before the purchase.
So now that I have this thing, and it's apparently dangerous to shoot, where do I need to start to get it fixed? I understand I will probably be replacing rollers (either +2 or +4?), but what else? I'm pretty mechanically inclined, but I'm no gunsmith. Since I'm not the original purchaser, do I have any recourse with Century?
Guys, I know a lot of this info has been gone over before, but if you can just bare with me, I'm trying to find the most direct info I can so I can fix this thing and not (still) feel like I got bent over.

[gw11]

clutchdust


Edited by me for a I said some things I should not have!
Sorry!

Take it a Smith!
gw11

[clutchdust]

gw11, I was hoping you would check in since you seem to be pretty knowledgeable. Feel free to post whatever you want. It's the internet. If I can't take some internet jabs, I don't need to be on it.
I did do a lot of research on the stickies and there's a lot of info there. It's just the sorting through it all, and I'm a little too much ADD.
If it's something I can do, I'd really rather take care of it myself. Not only will it be cheaper, but I'd like to actually learn about what I'm shooting. As a car guy, I have much more respect for people who build a car themselves than those that just write a check and pick it up from the shop a few months later.

[Van loos]

Procedure:
-Check bolt head dimensions. Wrong ? Change for an ungrinded one.
-Cleaning, cleaning and cleaning.
-Check bolt gap ( BG), remember rifle fired !
-Change locking piece.
-Check BG.
- Change locking lever.
-Check BG.
-Repress the barrel.
-Check BG.

Anywhre in the midle of this process you will get the proper BG.
Better soon than latter, and cheaper.

[clutchdust]

I have a question about identifying the rollers. One thing I did notice on mine is that the rollers sit differently in the bolt. Hard to understand but let me see how I do here. If I hold the bolt horizontal but with the left side up, the roller sits inside the bolt at a different height than the right side roller when it's pointing up.
Does that make sense?
It makes me think that possibly the rollers are different.

[gw11]

How the Rollers sit outside the gun mean "0" .
"Calipers" for questions on roller size.

[clutchdust]

Alright, so here's what I have so far. I measured the bolt and got 1.823", so I'm assuming that means this bolt has been ground (?). It also appears to have standard size rollers in it.
Also, the pin carrier (sorry I don't have the nomenclature down. The piece inside the bolt that pushes the rollers out) has distinct wear in the locked position. It's not enough to feel with a finger but I can see it with the way the light breaks on it. Basically, it looks more like a high spot in between the area where the rollers are locked and where they sit inside the bolt. Make sense? So is that a big deal?
Now get this. After reassembly, I do the same procedure, lock, fire, flip and measure and now I'm between .004 and .005". I can get .005" in there but it's pretty snug. Should I still bother with changing rollers? If so, I probably should go to +2, right?
At least I have a better understanding of how this thing works now. I was getting pretty close to just posting it on the local trader and saying "adios".

[Cabinetman]

Ok, maybe you're looking at this incorrectly and getting nervous for no reason.

First of all, I have NEVER read about ANY CETME blowing up from a "bad" bolt gap. That being said, the stats say you should have a 10-12 thousands gap. That's not much but it is something. Are you measuring it correctly? Allow me to just make sure:

Turn your rifle over, remove the mag so you can see into the mag well. Rack the bolt all the way back and let it go into battery under it's own spring loaded power. Now, take a feeler gauge (start with a .0010 feeler) and try to stick it between the face of the bolt and the chamber. It should just slide in. If it does, you're good to go. IF it doesn't, keep sliding in other gauges until one does slide in. Then report back with your measurement. Most guys can't tell 10 thousands by eye. I don't understand what your 1.8 measuremet referred to. Here's a photo to help:




Hopefully this will put your mind at ease!

Rome

[clutchdust]

Yep, that's where I'm measuring. And that's where I get the .004-.005" range. The way I'm reading all the other threads is that .004" is just barely usable and needs to be addressed.
The 1.823" measurement is based on several of the other bolt threads that actually measure the length of the bolt itself. My understanding is that it is supposed to measure 1.835" (I think), anything significantly less means that the assembler ground the bolt to manufacture the proper bolt gap, which is a falacy.
I'm learning these things and there's a boatload of info in this section, but it could take weeks to actually get it all digested. I'll get there, with the patience of all the knowledgeable people on this forum, I'll get there.
Thanks.

[EDIT] Matching pictures. Here's mine with the gauge in the gap. This is a very snug .005". .004" glides right in the gap.

[Van loos]

Check BG with gun fired.
New bolt head size is 46.60 mm, if not wrong 1.83".
If bolt is shorter, BG will be bigger in same way, but its artificial.
So this will be first step to cure it.
I think.

[clutchdust]

Ya, I'll go burn 20 rounds tomorrow and check it again. Anybody else sell the rollers? Or do I just need to go back to Century?

[gw11]

Your Gun is not Safe to Fire.
But it has been done before! Good Luck!

If you have a problem understanding what people are talking about [as far as Part Names] Then you have a problem paying attention to what you are told! This will not work! Most all the info you need has already been said to you but you do not understand what you have been told. [This is a waste of time] Get yourself a schematic and learn what people are telling you. Or at least Pin Point what you don't understand.
If you have a need to keep passing over what you don't know, then keep doing it and Blow your face off from your ignorance, I don't Care!


As far as where your Rollers are sitting in the trunion and how the Gun Safely Functions, with a .012" undersized Bolt. Your Bolt Gap is -.008" [That's a Minus .008"]

+4 rollers will give you [Minus .004]

A new Locking Piece will help some [from your description maybe .004"] gives you a .000" Bolt gap.

Your Carrier is also Smashing into the Cocking Handle Support every time it cycles or the forward tube has been Ground [shortened] to achieve a Gap at the Support. If it is hitting the Support, you have Less Gap that what I just said.


What you need to do is purchase a New Complete Bolt/Carrier assembly and Locking Piece and a set of standard Rollers [measure them] . and send the gun out to a smith and have it re-barreled.
APEX Gun Parts has New Bolt/Carrier assemblies for $75.00.

gw11

[srinde]

Geeze louise. I do not see any reason to abuse the poor guy. He came here looking for help.

[clutchdust]

Hey, it's no big deal. It's just the internet. I can empathize with gw11's frustration. I experience it myself on other, unrelated forums. Maybe what gw11 doesn't understand is there's just a massive amount of info here that comes as second nature to him now. I'm still learning, so I think I get it but then don't, then do, but wait, what? You know.
Now to others who may want to exercise a little more patients, what's the correct bolt gap? I thought it was in the .004-.020" range, is that wrong? I downloaded a manual (I think gw11 even posted it) but it doesn't specify bolt gap.
I also think based on the above posted measurements that the bolt has been milled. Is this necessarily a bad thing? I mean, does it condemn the bolt? Or can it be reused and the gap be properly achieved?
I guess it makes sense that .004" on a milled bolt would need rectifying. But I don't know if I can rectify with rollers, or replacing the bolt. I guess gw11 is trying to beat me over the head to tell me I have to replace the bolt.
So I need to replace the bolt before I do anything else, or my numbers won't mean anything.
Am I getting it?

[EDIT]
OK, I reread some of the previous posts and I think I'm starting to understand what's being said. In effect, what I would need (if such parts existed) would be +10 rollers, or higher, just to get it within the normal tolerances. Since those rollers don't exist, I need to replace that bolt. But do I need to replace the entire thing? Is just the bolt itself not available? Is just replacing the bolt itself a big no-no?

[jdub]

Replace locking piece and bolt head.

https://www.apexgunparts.com/product...products_id/70

cetme compatability and + sized rollers.

http://robertrtg.com/cetmeinfo.html

With a new LP and BH and + sized rollers you may have a neg gap or some gap. Dunno, most likely neg.. You need a barrel repress, goto militaryfirearms.com. I am not a member there but they can help too. Check inside the bore near the muzzle break for a protruding pin as well.
Slowly file down the bolt carrier until the charging handle has just a tiny bit of play. Too much and it wont cam the bolt...

You will like this gun when it gets running good luck.. This is the las time I will post on this b/c the forum is acting weird.......

[clutchdust]

O.K. Hang on. Wait a minute. If I change out the bolt head or entire carrier, are some of you thinking I'll need to repress the barrel??? F***! This $hi+ is getting expensive. Sounds like by the time I get done, I'll have spent close to a grand for a $600 rifle! If I have to go all through this thing to make it f***ing safe to fire, I think I'll just throw the thing in the safe until the world comes to an end, then just use it for barter. Now I really feel like I got screwed. F***ing stupid impulse buy. I think I'll stick to my SKSs and ARs and leave these POSs to you guys. :::

[Cabinetman]

Geeze........this is getting out of hand, not unlike the past when this was first discovered. Let's let cooler heads prevail.

I'm going to refer you to one of my original comments; Google this any way you want (CETME Failures....CETME explodes....CETME ground bolt failure) and please find some posts where there is a systemic issue that is causing CETMEs to explode or fire out of battery or some other destructive activity. I'll save you the trouble (although you should spend some time reading.) There aren't any destructive failures.

Crooked welds, poor assembly, bad parts, etc., etc. Sure you'll find a bunch of that but no deadly or maiming failures. I'm not saying that ground bolts are appropriate or correct. I am saying, however, that with thousands upon thousands of these rifles being sold by CAI to the public that if there were an ultra serious issue, there would have been a bunch of reports about exploding or out-of-battery CETMEs out there.

The bottom line, however, is that there just aren't any.

Remember the MAS 49/56 saga from CAI? Remember the big issue with how their chambers were cut by angry beavers and rifles became clubs in droves because they were transformed from 7.5 French to NATO caliber? Well, turns out that while it did happen, it happened in very small number because the only recorded issue of rifles turning into clubs was reported over and over on the internet. Yes, that problem did happen but it was over reported. And, no!....I don't work for CAI or have any interest in defending them or condemning them either. I'm just saying that keep your cool here.

When it was discovered that CETMEs had ground bolts, it was a concern no doubt. It was a shortcut CAI should not have introduced. Remember the forum dedicated to the CETME here at gunboards? There was wild speculation about grounds bolts going on for months on end. Still, only a small percentage of CETME owners post at the forums and a lot of these rifles are in the field shooting NATO ammo just fine. Heck, I'll bet the bulk of the owners are shooting commercial .308 in them without a hitch. Still, they have ground bolts and may encounter issues in the future but right now, there simply hasn't been the plethora of damaged shooters and failed rifles that we might expect with a systemic problem.

So, Clutchdust, take a deep breath, stand back, and examine the issue.

What I would do if I were you is simply Call Century. Speak to someone there who knows the subject and tell them what you measure for your boltgap. Then ask them what can be done....should be done......and what they will do about a short bolt gap. Tell them that you are concerned. Get a name. See if they'll help you or if they even feel you need help. That's where you should start.

I've owned one for years and even shot another one over the weekend. When I asked the owner if he measured the bolt-gap, he looked at me like I had two heads. Do you think that the basic owner is going to do a bolt-gap measurement with a feeler gauge on a regular basis or do you think these owners are going to go out, load up some mags, and had at it for some fun? I believe that the bulk of the owners are out there shooting these rifles and don't have a wit of knowledge about bolt gaps and ground bolts. If it were a super serious issue that would lose someone's fingers or an eye or two, there would be a TON of stuff on the 'net but there just isn't.

There was a problem early on with the original Hesse receivers which were made from a sub-par material. The rollers would 'buldge' the metal. The second generation of receivers were stainless steel and were 100% better than the original. The third, and final iteration of receives were made from steel that was more closely made to original specs and were also excellent replacements. Which do you have? Only CAI can tell you by your serial number.

So, take this info for what it's worth. Study the subject, make some decisions, and enjoy the rifle.

Rome

[clutchdust]

Alright, I've calmed down a bit now.
I let some of this get to me because it sounds like a lot of the advice boils down to "rebuild the rifle".
What I'm trying to understand is, if I get a bolt of the correct dimensions and the gap is right, is there really anything else I need to do? What's with all this 'pressing barrels' and buffer tubes and stuff?
I'm just trying to learn this stuff and, on this board, it sounds like the Century's are the biggest POSs out there, mere thousandths of an inch from exploding!
Going back to what gw11 stated, the way mine is set up now, I have something like negative .012 clearance due to the bolt grind. So if I replace it with a new, unground bolt and a set of rollers that gives me about .016" clearance, I should be alright, right?
I mean, please, correct me if I'm wrong (I really am trying to understand this). I have verified by caliper that my bolt is 1.823, ~.012" off, so it's been ground. I currently get .004", which is a false reading because the bolt has been ground. So if I get a bolt at the original specs of ~1.835 plus my current .004", that should make .012" + .004" = .016". And, to accomodate for future wear, I could go ahead and get a set of + size rollers to give me a bit more bolt gap and all is well. Right?
Where am I wrong?

[gw11]

Sorry if you people don't like my directness. But when suggestions are made and there is no follow up or interest is issues that are obvious, it becomes a pain in the butt to attempt to keep explaining everything over and over again.

[ http://forums.gunboards.com/showthread.php?t=132942 ]


And be sure to understand that you can certainly do what ever you wish and you can certainly form your own independent opinions on how these gun function and how they should be maintained.

Once again!
[As far as where your Rollers are sitting in the trunion and how the Gun Safely Functions, with a .012" undersized Bolt. Your Bolt Gap is -.008" [That's a Minus .008"]

What this means is with a New Unground Bolt your Bolt Gap is MINUS .008".
With a New Locking Piece your Gap may raise to approx. MINUS .004"
And if you install +4 Rollers Your Gap May raise to .000"

The only other thing that May Help is if your bolt is worn were the Rollers contact the inside forward face of the Roller Slot. [ every .001" of wear will equal approx 3.5 times that amount in Bolt Gap loss].


Also if you choose to pass over the condition of your gun as some have suggested, keep in mind that your current Gap your Bolt is locking at a deminished amount from what it was designed.

Again as mentioned here, By all means turn a blind eye to Bolt gap and Load Up any ammo you wish, cock that sucker and have some fun!

But from now on you can form your own opinions and I am sure the good folks here will guide you safely home. LMAO!

[clutchdust]

You know, it's a damn shame. Here I think you (gw11) are exceptionally knowledgeable. I'm asking questions because I'm trying to ****ing understand, and you're being an asshat. So, partner, I respect your knowledge, but if you're just going to cock off with all the attitude, then I'm sure there are other threads in which you can participate. I'm beginning to wonder if you just like it. I mean, you've made your opinion known, even accused me of ignoring your advice and advised me to go off and have fun, safety be damned. And yet you come back for more.
Now, I would love to be able to sit down, face to face, and pull this thing apart with someone who has intimate knowledge and do the whole "hands on" warm and fuzzy thing. I'm a little dense on the conceptualizing, but hell on wheels if I can see it in person. But seeing as how this is the internet, IT MAY TAKE A COUPLE TIMES!
So, gw, not nice knowing ya! Next time you want to post, just go have a beer on me.
To everyone else who's being constructive, thanks, please keep it coming.
This has been by far the most frustrating firearm I own. It's even worse because I spent money I could have saved for something less, well, sucky. I've been wanting an M14 but the budget just didn't allow it and I figured this would be a cheap way to get into a .308. Lesson learned.
Maybe I can get this right and actually enjoy this thing.

[clutchdust]

So now, back to your regularly scheduled technical thread. So based on what I'm reading....
Wait a minute, I just need to get this out.
gw, you ever think that maybe you're saying something and I'm hearing (reading) something, and I don't understand what you're saying? Hmmm? Ever think that maybe I'm not ignoring you, but misunderstanding? Ever think that maybe you're the one who can't explain something well enough that you shouldn't bother with novices? Or does that just not matter? In your world, do all new owners need to be able to recite the manual, chapter and verse, before he/she is worthy of asking simple f***ing questions?
Jeez!
OK, I'm back.
So, based on some of the previous posts (despite snarky posts, there's occasionally some good info, I think), even if I put in a new bolt, I may still be short on gap. What is out of tolerances that a new bolt wouldn't correct? Is that why I need the entire carrier?
Now here's where my understanding breaks down. If the relation of the bolt to the chamber is correct, isn't that the most critical measurement? Isn't that what all this "bolt gap" stuff is all about? Not that I want anything damaged, but after years of service, I could deal with having to replace a tube or something. I just don't want a round firing out of battery. Looking at the system, I'm not even sure how that's possible, but this is the first DBB system I've worked on.

[clutchdust]

Alright, I have this thing apart and I'm looking at everything. So what I can't figure out just from looking at it is how exactly it locks. I mean I see that the locking piece pushes out the rollers. But is that all that holds the bolt in place??? Just the rollers against the side of the housing??? I see distinct marks on the side of that guide where the bolt rides that I assume is the rollers locking the bolt, but I also see an even more pronounced notch on the guides at the back of the bolt's stroke. Is that normal?

OK, just looked at it again. Even slid the bolt home and I can see the rollers locking into place (not where I was thinking). But what are the marks I see on the guides? I said it before and I'll say it again (for the reading impaired) but I'm no Gunsmith. I do like learning, even though I may throw a tantrum every now and then. So my rudimentary engineering knowledge tells me that we should have a clearance between the bolt face and the chamber, to accomodate heat expansion. I'd guess somewhere in the .010-.020" range. Or is the bolt supposed to butt right up against the chamber? If grinding the bolt to achieve this false clearance is wrong, what locates the carrier during the firing cycle? I mean, I can't see it being free floating while the bolt head is locked in place. And with the recoil spring pushing it forward, there must be some form of positive stop, aside from the bolt, if I'm looking for ~.016".
Speaking of, where the hell is a full breakdown with nomenclature? I printed out this manual: http://pdf.textfiles.com/manuals/FIREARMS/cetme_s.pdf, but it doesn't specify "trunion", so I'm not sure where the barrel ends and the trunion begins. It also doesn't break down the cocking tube and stuff.
So looking at this thing and trying to reverse engineer it (no thanks to certain members) I surmise that the real issue with bolt gap is that having zero or less bolt gap could prevent the part (not named in my manual, but I'll call it the "locking lever") on the carrier from fully seating on the bolt, thus presenting the possibility of the bolt unlocking and flying back at the moment of ignition. Is that about right?

Oh yeah, and I also noticed very distinct sanding/grinding marks on the front of the carrier tube. Par for the course Century, I suppose.

[clutchdust]

Is the trunion the same thing as the barrel extension?

[Cabinetman]

Well, you've got the best manual out there for this rifle. IT was scanned and put up on the 'net by another well known poster a few years back. I still remember when it was done, by crackie (feining old man's voice). I'm not that old but I have been collecting for a while.

The CETME has a unique firing system and is why I find it fascinating. When the round fires, the exploding gasses try to ram the bolt backwards toward you. What happens instead is that the rollers instantly expand against the receiver body and block the bolt from going rearward. That's until the bullet has passed through the barrel and the gas pressure has diminished a bit. Then, after most of the pressure has exited through the muzzle, the remaining pressure is just enough to allow the rollers to retract and then the bolt slams back against the spring, ejecting the old brass and picking up a new round off the bolt as it returns forward. In addition, the remaining gas "floats" out the old brass assisting the extractor claw with extraction while the bolt, itself, does the ejecting. That's why the brass has black stripes on it. It usually also has a flat ding in the throat of the brass where it hits the receiver on the way out......if you can find it. The darned CETME tosses brass into the strastosphere, at least a good 15' away in to an nice pile.

In the early days of this rifle at CAI, Hesse receivers were soft. What happened was that eventually the slamming of the rollers into the soft receiver metal was causing the metal to "bulge" at that position. This, of course, would not do because the rollers wouldn't lock in battery but would push back which, of couse, exposed brass. This is not a good thing. Larger rollers would do the trick for a while until the bigger rollers exanded the bulge ever further.

The next iteration of receiver, however, was SS and it would not bulge allowing for standard rollers. The last iteration was a metal more closely related to the actual CETME and G3 rifles. It's strong enough to resist the bulge at the roller engagment area.

If you are concerned about lockup and bolt gap, you may want to pursue a new bolt setup from one of the links found above. Just check the headspace after you install it. These rifles do require welding when they are assembled. If the headspace is excessive it can be a problem. The only other thing I would try would be to shoot one round with your rifle as suggested. Immediately check that brass and check the bolt gap without moving the charging handle. If the brass looks good and the bolt gap has not altered, I would just enjoy the rifle. Check for bulges at the roller area on the receiver, however. They will be quite evident.

Rome

[clutchdust]

Thanks, Rome.
After looking at it a bit more, I'm beginning to get the hang of the operating system but I still have a long way to go.
Looking at mine, it would appear that the rollers engage a machined piece inside the receiver, it doesn't look like sheetmetal. Am I seeing that correctly? Or is that actually part of the sheetmetal receiver? So is there a complete breakdown somewhere? I'm really interested to see the barrel and how it fits into the receiver. Is the trunion separate from the barrel? It would really help me conceptualize this thing if I could see all the constituent parts individually.
Lemme run this by you and see if I have this figured out. When the charging handle is slapped, the recoil spring slams the bolt home. The bolt carrier meets a positive stop with the trunion(?), locating the bold head between the carrier and chamber. This is the illusive bolt gap issue we're all chasing. So the issue of grinding the bolt to make the gap is false because it changes the relationship of the dimension between the rollers and the bolt head. But the real culprit is the distance of the chamber pressed into the receiver. Is that about right? That kind of makes sense from what I can see.

[Cabinetman]

Check this link here and I believe you'll find most if not all the answers in some of the great photos of CETME parts.

http://knopester.com/CETME/

Rome

[clutchdust]

Thanks! That's some of the info I was looking for. So now that I can see all the constituent parts, it does look like I was thinking. The only thing I can't quite figure out from the pictures is the relation of the rollers to the trunion. To me, it looks like the rollers engage the trunion but it seems everybody is saying they engage the sheetmetal receiver. From an engineering standpoint, that is an exceptionally poor decision. With headspace and bolt gap being such a critical dimension, it would make far more sense to locate everything off the trunion.

[Super B]

This might help

http://www.youtube.com/watch?v=MFESb8TK7ZA

http://www.youtube.com/watch?v=UoLrj...eature=related