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 Loose trigger pin
EndgameSTG  [Member]
9/11/2010 3:33:06 PM EST
The trigger pin on my lower (the one that holds the trigger mechanism in place, just forward of the safety selector externally), is a bit loose. I feel it moving a bit when I push it with my fingers on either side of the lower. It came loose once with one side protruding and another stuck inside the receiver, and I had to reassemble the lower to get it back into position. I know that with enough firing, the same thing will eventually happen again. It begins to protrude after running a mag through the gun at the range.

So how do I fix this permanently? I thought about fixing it in place with some adhesive, but I want to be able to disassemble the lower if necessary in the future. Is the hole for the pin too wide, which would mean a problem with the lower itself (it's under warranty)? Is putting in a new pin likely to fix the problem?
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a308garand  [Team Member]
9/11/2010 3:45:17 PM EST
1)Ensure your hammer spring is installed correctly. The legs of that spring rest in grooves on either side of the trigger pin, retaining it in the receiver.
See picture from Dano523 in this post:
http://www.ar15.com/forums/topic.html?b=3&f=66&t=509851

2)If the hammer spring is good, then look at the trigger itself. Are the sides of the trigger blocking the trigger pin grooves? If so, lightly stone each side to allow the spring legs room enough to sit on the pin.

3)Is the trigger pin in spec,,,,,are the grooves cut enough to allow the thing to be retained? Get a new pin.

4)Another solution is to use a KNS anti-walk add on to your receiver.
http://www.bravocompanyusa.com/KNS-Precision-Non-Rotating-Trigger-Hammer-Pins-p/kns%20trigger%20hammer%20154%20pins.htm
EndgameSTG  [Member]
9/11/2010 3:50:37 PM EST
Originally Posted By a308garand:
1)Ensure your hammer spring is installed correctly. The legs of that spring rest in grooves on either side of the trigger pin, retaining it in the receiver.
See picture from Dano523 in this post:
http://www.ar15.com/forums/topic.html?b=3&f=66&t=509851

2)If the hammer spring is good, then look at the trigger itself. Are the sides of the trigger blocking the trigger pin grooves? If so, lightly stone each side to allow the spring legs room enough to sit on the pin.

3)Is the trigger pin in spec,,,,,are the grooves cut enough to allow the thing to be retained? Get a new pin.

4)Another solution is to use a KNS anti-walk add on to your receiver.
http://www.bravocompanyusa.com/KNS-Precision-Non-Rotating-Trigger-Hammer-Pins-p/kns%20trigger%20hammer%20154%20pins.htm


Thanks a bunch. I'll give all of these a try.
altopwescap  [Member]
9/12/2010 9:18:04 AM EST
The J-spring in the hammer is missing or damaged.
Dano523  [Moderator]
9/12/2010 12:30:58 PM EST
Originally Posted By altopwescap:
The J-spring in the hammer is missing or damaged.


The J spring only holds in the hammer pin, not the trigger pin.

The trigger pin is held in by the hammer spring legs resting on top of the hammer pin in the annular groove.

If the spring is installed wind correct, then legs on top of the pin and one of the legs in the groove, and still the pin slipping out, it could be that the groove is too narrow and shallow for the spring leg. If that is the case, then just drill spin the pin while using a small file to deepen and widen the side groove in the pin.

Note: both hammer and trigger pins are the same. The hammer uses the center groove for the hammer J spring, while the trigger uses the side groove for one of the hammer spring legs to seat in it.
FLchuck8  [Team Member]
9/12/2010 12:51:03 PM EST
Originally Posted By altopwescap:
The J-spring in the hammer is missing or damaged.


The J-spring retains the hammer pin. I think he is describing the trigger pin. I would check the above post regarding the legs of the hammer spring, if this is not the issue, KNS pins are a inexpensive addition that will prevent both pin walk and pin rotation, therefore wear of your lower. They are also considerably stronger than standard pins of which I have broken a few from use in aging gun.
altopwescap  [Member]
9/12/2010 4:35:09 PM EST
My bad!!!!!!!! Misread OP
RangeWarrior  [Team Member]
9/12/2010 4:41:43 PM EST
+1 on the spring placement... if all else fails buy a set of KNS pins
UncivilEngineer  [Team Member]
9/12/2010 4:43:51 PM EST

Originally Posted By Dano523:
Originally Posted By altopwescap:
The J-spring in the hammer is missing or damaged.


The J spring only holds in the hammer pin, not the trigger pin.

The trigger pin is held in by the hammer spring legs resting on top of the hammer pin in the annular groove.

If the spring is installed wind correct, then legs on top of the pin and one of the legs in the groove, and still the pin slipping out, it could be that the groove is too narrow and shallow for the spring leg. If that is the case, then just drill spin the pin while using a small file to deepen and widen the side groove in the pin.

Note: both hammer and trigger pins are the same. The hammer uses the center groove for the hammer J spring, while the trigger uses the side groove for one of the hammer spring legs to seat in it.

The Spikes LPKs I just installed all had separate trigger and hammer pins. Never seen it before, but they do exist.

ezlife45  [Member]
9/17/2010 4:24:01 PM EST
I have successfully used loctite to prevent pins from walking/spinning. You just need to be a little more careful that you don't loctite the hammer pin to the hammer instead of the receiver. If you ever need to remove it shouldn't take too much to loosen up. I had the loctite blue. Not as strong as the red.
Dano523  [Moderator]
9/18/2010 4:17:50 AM EST
Originally Posted By ezlife45:
I have successfully used loctite to prevent pins from walking/spinning. You just need to be a little more careful that you don't loctite the hammer pin to the hammer instead of the receiver. If you ever need to remove it shouldn't take too much to loosen up. I had the loctite blue. Not as strong as the red.


They are supposed to spin, hence the J spring to the hammer pin has more tension than the pin to the receiver channels.

Walking is just a maker of making sure the trigger spring and hammer J spring has good retention on the annular grooves of the pins.
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