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Old 12-13-2017, 02:53 PM   #1
shane545
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Default Oversize Trunnion/parts?

Well, I am still working on my first build, now getting around to it again, and having an issue, may have to get a new barrel, but I think my trunnion is oversize, I'v tried a selection of 3 original barrels, and all are spinners, go in with just finger pressure and turn easily., on the journal is a 3 on top where the rear sight slides, over, a 3 or an 8 stamped on the left side infront of the barrel pin channel, and an off F or something on the front where the barrel would slide into., put some photos on below., measured with cheap Pittsburgh digital calipers

Barrel Journal in trunnion measured: 22.89 mm --- 0.901 inch +/1 a thousandth

the rear sight block is ID: 18.46 mm -- 0.727 inch +/1 a thousandth

The Gas block ID: 15.90 mm -- 0.626 inch +/1 a thousandth

The Front sight block ID: 14.86mm -- 0.585 inch +/1 a thousandth







any help or suggestions would be appreciated.
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M70B1 Build Oversize Trunnion/Parts Help? : http://www.akfiles.com/forums/showthread.php?t=328858
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Old 12-13-2017, 04:42 PM   #2
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What is the barrel measuring? Considering you are using calipers to measure, the dimensions are tight. The barrel trunion journal diameter should be .907 so if you're using finger pressure to push into a .901 hole, you are the man.
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Old 12-13-2017, 04:54 PM   #3
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I found this in a search. I guess the parts would be .003-.006 smaller but that sounds a little heavy to me if these numbers are right.
YUGO M70 PATTERN BARREL:
Chamber .908" (23mm w/ .003 - .006" press fit)
Rear Sight Base .730" (18.5mm w/ .003 - .006" press fit)
Handguard Retainer .687" 8.4375"/ 214.31mm from breech face (8 7/16)
Gas Block .630" (16mm w/ .003 - .006" press fit)
Front Sight Base .593" (15mm w/ .003 - .006" press fit)
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Old 12-13-2017, 05:27 PM   #4
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you are correct, I must have slipped as I re-checked the barrel channel diameter and it is measureing at 0.906-0.907.

2 barrels measure 0.905 and 0.906, and third measures 0.904

I'll remeasure my gas block, rear sight block and front sight block soon, then measure the 3 barrels and see if any are good in all 3 spots
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Old 12-13-2017, 06:09 PM   #5
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If you trust your tools and that front trunnion measures .906-908 then you need to find a standard sized barrel. I cant believe all three barrels are too small unless they have been modified.

In other words. Provided the measurements are accurate the front trunnion is of standard size and not the issue here.
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Old 12-13-2017, 06:18 PM   #6
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Quote:
Originally Posted by pinakar View Post
If you trust your tools and that front trunnion measures .906-908 then you need to find a standard sized barrel. I cant believe all three barrels are too small unless they have been modified.

In other words. Provided the measurements are accurate the front trunnion is of standard size and not the issue here.
I was thinking the same thing, wouldn't want to knurl a bad barrel but two the same is odd.
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Old 12-13-2017, 06:54 PM   #7
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well, I know my calipers aren't the best thing in the world, but on the original barrel sections, checking each spot, I was getting.

chamber OD: 0.907-0.908

RSB: 0.727-0.728

GB: 0.629-0.630

FSB: 0.590-0.591

and on one of the barrels that showed promise, without drilling the holes and riveting the trunnion in, just press fit into receiver and bolt sliding without rails it closed on a go gauge, and didn't close on a no go, using a punch to hold the barrel firm into the trunnion in place of the barrel pin, and it's measurements were:

Chamber OD: 905-906 (would need knurled(?))

RSB: 0.726(?)

GB: 0.625(?)

FSB: 0.585(?)

I'll measure the journals of the RSB/GB/and FSB again in a few and edit with the results.
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Old 12-14-2017, 03:41 PM   #8
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Why the hell are we talking about rsb,gb, and fsb journals? Are they loose too?
Find the biggest trunnion journal barrel of the three (best fit for trunnion) knurl it and build the thing
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Old 12-14-2017, 07:59 PM   #9
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Just got my hand knurling tool today, knurled my barrel fits great now tight as can be, if you were closer could knurl it in a few mins
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Old 12-14-2017, 08:01 PM   #10
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Originally Posted by Phrygian68 View Post
Just got my hand knurling tool today, knurled my barrel fits great now tight as can be, if you were closer could knurl it in a few mins
That's good to hear, and yea, it is sad that where I live there is not really anyone that does building, and I don't know if I'd be able to send the barrel to anyone to have knurled or anything, though first I gotta pin it (as it's an original barrel), to be sure it head spaces before I go though the trouble of having it knurled or what not.
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Old 12-14-2017, 08:06 PM   #11
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you need to have it knurled 1st then properly pressed into the trunnion, check headspace and then drill, your only a few hours away i would do it if your interested, i would suggest you record a short 10-15 sec video clip with your phone and post, let's see what the fit looks like
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Old 12-14-2017, 08:08 PM   #12
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Interesting, I'll do the video in the morning and post it here, see what you and the others think on the matter, and it's an original barrel so thole is already drilled, but lineing it up and using a punch to hold it, it seems to head space decently, closes on go, and don't close on no go no matter how much I force it, but I'll check again once I pin it to the trunnion at some point.
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Old 12-14-2017, 11:21 PM   #13
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Quote:
Originally Posted by shane545 View Post
Interesting, I'll do the video in the morning and post it here, see what you and the others think on the matter, and it's an original barrel so thole is already drilled, but lineing it up and using a punch to hold it, it seems to head space decently, closes on go, and don't close on no go no matter how much I force it, but I'll check again once I pin it to the trunnion at some point.
before you press the bbl pin in you should use some sorta sharp pointed object to use as a feeler gauge to make sure that the pin channel is lined up exactly

https://www.harborfreight.com/media/...mage_16048.jpg

check the hs then press the bbl pin & recheck hs after
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Old 12-19-2017, 01:01 PM   #14
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If you have a local machine shop fix the journals, it can be done so it is a very acceptable and thorough repair and hidden from view. Here's one of many I did "back in the day".

Records show this diameter had to be raised about 0.001" (0,025mm). The correct knurl pitch was calculated for the diameter and impressed enough to raise the surface about 0.012"/0.015" (0,3mm/0,4mm) total diametric gain and then machined to the correct size. Notice there is a loss of surface contact no more than 10%. Taking this into account I would increase the interference from the minimum of 0.001" (0,025mm) to about 0.0015" (0,040mm).

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Old 12-19-2017, 08:37 PM   #15
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Guys note that Robert did not knurl the whole journal just the are the trunion bore touches . nobody will see the work once installed .

Looks nice BTW
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