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Old 06-24-2011, 10:18 AM   #1
Richard Erichsen
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Default Yugo M70 bolt sticking while rotating in trunnion

I'm trying to work out what's happening on my M70 build. The trunnion was virgin and I suspect the majority of the problem, if not the root cause is lug clearance.

When the bolt and carrier are pushed forward, it sticks a half inch prior to closure. Smacking it forward doesn't advance it more than a few fractions of an inch, then it stops advancing completely. I've tried 3 spare bolts and 2 carriers to make sure that's not the issue, no dice. I removed the gas tube to eliminate that as a possible source of the problem (lots of clearance around the piston, I could wrap the piston in several layers of paper and still push it though the tube without much resistance). I then removed the bolt from the carrier, with the gas tube refitted and was able to push the carrier to the closed position without difficulty. That would seem to rule out a gas piston/gas tube clearance issue.

Inserting the bolt by itself without the carrier and into the barrel trunnion had an interesting result: The bolt doesn't seem to rotate all the way clockwise. It feels like it is not completing the rotation for a full lock. Comparing this weapon to the other M70, the bolt does not seem to be rotating as far clockwise. That lack of full rotation would seem to explain why the carrier can't move all the way forward.

Assuming I diagnosed this correctly, the next step will be fixing it. I don't want to take off much metal from the lug area, and the angles and clearance are so small that most hand tools are going to be very clumsy if not impossible to reach the spot, or see what I'm doing. Since I work on cars as well, I hav on hand several grades of abrasive cutting compound which I can follow up with fine lapping compound. My thought is that using the bolt as my tool, that the cutting compound will be forgiving enough that slowly but surely I will be able to polish out the lug recesses. With enough patience and elbow grease, I'm inclined to believe I can get the bolt to rotate freely.

Have I missed anything in the diagnosis? Any other suggestions on smoothing out the lug area to clean up lug clearance?

R
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Old 06-24-2011, 12:46 PM   #2
camaro1509
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Default

i got cai m70ab2 with the black stock n us barrel i polished the bolt now it wont cycle right
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Old 06-24-2011, 01:11 PM   #3
Richard Erichsen
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Quote:
Originally Posted by camaro1509
i got cai m70ab2 with the black stock n us barrel i polished the bolt now it wont cycle right
Is that a warning Camero1509?

Why did you polish the bolt? Was there a specific problem you were trying to solve, or did you think it would improve the action?

Where did you polish it and with what kind of tool? I'm planning to do my work by hand to avoid powertool over-exuberance (you can't put metal back near as easy as taking it off). I don't suppose you had a sticky bolt lug to barrel trunnion interface like I'm experiencing, did you?

R

Last edited by Richard Erichsen; 06-24-2011 at 01:38 PM.
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Old 06-25-2011, 01:50 PM   #4
Richard Erichsen
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Default UPDATE: Headspace too tight

It turns out my headspace was too tight, that was the real problem. I mixed up my bolts when I had three of my Yugos apart. Oops. The right bolt had some lapping on the bolt face to make the area more regular and adjust the headspace outward.

There are areas of roughness, but just shooting it will even that out even without lapping, in any case, that was NOT my root cause. Pay attention to headspace and if you had any fitting of the bolt to the barrel/trunnion, electropen the bolt with the serial number of the trunnion if you have several AKs or you will do what I just did.

R
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