View Full Version : Pivot pin not 'locking' properly
roadDOG.19
10-22-11, 23:18
First AR build here, so maybe I am doing something wrong you can point out. I am having an issue with the detent not catching the pivot pin when in the closed position. Springs and detents seem fine, as they both work for the takedown pin. Attached is a pic of what looks to be an alignment issue between the pivot pin and the receiver. Any thoughts?
DPMS lower
DD LPK
10070
Megalomaniac
10-22-11, 23:37
I can't say 100% for sure but to me it looks like the detent is larger than the depression in the pivot pin, try popping it out and fitting it into the depression and see if it even mates.
Are you sure its the correct spring? Or detent for that matter?
You might have mixed a spring up.
If you used a DD LPK then I can guarantee the parts are perfect.
Double check your work
roadDOG.19
10-23-11, 00:44
The detent fits the pivot pin fine.
Not 100% sure, but I think I have the right springs and detents. I have two springs and two detents that are identical, seems right according to the DD packaging. Pulled the grip to look at the selector detent spring, and it is shorter and heavier gauge than the two I am using for the pins. Does this sound correct?
Just for clarification, the takedown pin locks fine in both positions. The pivot pin locks in the open position, but not when it is pushed in.
JR TACTICAL
10-23-11, 01:21
First off welcome to the forum
Ok, from your picture that is not a detent. That is a roll pin, you have the wrong part in the wrong area. Detends are small, brass colored pieces, atleast the ones you are going to use for the pivot and takedown pins. Do a re-cap on parts you used for your lower and im sure you will find a detent, do a good check and make sure you have all the correct parts in their right places. If not you may an unsafe build and may need a armorer or gunsmith to do it correct
JR TACTICAL
10-23-11, 01:23
The detent fits the pivot pin fine.
Not 100% sure, but I think I have the right springs and detents. I have two springs and two detents that are identical, seems right according to the DD packaging. Pulled the grip to look at the selector detent spring, and it is shorter and heavier gauge than the two I am using for the pins. Does this sound correct?
Just for clarification, the takedown pin locks fine in both positions. The pivot pin locks in the open position, but not when it is pushed in.
PM me PLEASE!!!
roadDOG.19
10-23-11, 01:47
Thank you for the welcome.
JR, that is the spring in the pic, not a roll pin. The detent is not in the pic though. Could not hold the detent and pivot pin in place and take a pic at the same time. The only reason I took the pic is because the alignment just didn't look right to me.
The detents for the takedown and pivot pins are silver in the DD LPK that I have.
I can try to get pics of whatever you need to see to be assured I have everything in the right place. Everything else works fine, except for the issue with the pivot pin.
JR TACTICAL
10-23-11, 02:01
Thank you for the welcome.
JR, that is the spring in the pic, not a roll pin. The detent is not in the pic though. Could not hold the detent and pivot pin in place and take a pic at the same time. The only reason I took the pic is because the alignment just didn't look right to me.
The detents for the takedown and pivot pins are silver in the DD LPK that I have.
I can try to get pics of whatever you need to see to be assured I have everything in the right place. Everything else works fine, except for the issue with the pivot pin.
Oh copy, it was a little fuzzy and looked just like a roll pin but i see it now. The alignment looks ok to me, funny about the detent color i just did a build for a guy 2 weeks ago and used a DD LPK and they looked brass colored to me, but back to the point, you should be able to set the spring and detent into the hole and they should stay there, i think you used the wrong spring. If i remember correctly my detent springs were a dark color and really skinney. If you cant fit the detent and spring in the hole without any pressure on them then you have the wrong spring. Try and take a few more pics and we will get this fixed, worse case get a new detent and spring from brownells it might cost you $1-$2 bucks ut lets try and fix it with what you have
roadDOG.19
10-23-11, 02:39
I attached two more pics here. One is the springs, detents and pins with the selector detent and spring for comparison. The other is the lower with the spring inserted, showing how far it protrudes.
10071
10072
... you should be able to set the spring and detent into the hole and they should stay there...
They will not stay. The detent and spring need to be compressed into the hole for the pivot pin to be installed.
In your first photo it appears the pivot pin, when closed, will contact the receiver and stop before the detent pin lines up with its recess in the pivot pin. Take some measurements to see if this is true. This could be an optical illusion in the photo.
If it is true there are several different solutions:
1 Remove material from the receiver to let the take down pin set farther in. (Really bad idea, but a solution)
2 Remove material from the head of the pivot pin where it contacts the receiver to let it set in farther. (Better idea)
3 Relocate/elongate the detent hole in the pivot pin so the detent engages it sooner. (Better idea)
4 Find a pivot pin that works with the receiver tolerances, without modification. (Best idea/solution)
roadDOG.19
10-23-11, 08:42
In your first photo it appears the pivot pin, when closed, will contact the receiver and stop before the detent pin lines up with its recess in the pivot pin. Take some measurements to see if this is true. This could be an optical illusion in the photo.
This is what I am seeing too. I will get some measurements today.
3 Relocate/elongate the detent hole in the pivot pin so the detent engages it sooner. (Better idea)
I am going to try this for now. Will also look at picking up some other pivot pins in the near future.
At first I thought it looked like maybe the detent/spring hole in the lower was drilled in the wrong place (too close in), but I looked at one of my bare lowers and it looks about right. Maybe and unfortunate tolerance stack up? I'd go with az doug's number 3. Also make sure the end of the detent that contacts the pin is the more pointed end.
How deep is the pivot pin detent spring tunne?l
lowdowndad
10-23-11, 13:01
Bad pivot pin perhaps? Maybe get a different one and try it or compare the two.
lowdowndad
Quiet-Matt
10-23-11, 14:48
It may be the camera angle, but it looks like the detent divot in the pin is not large enough and its drilled too far out.
yours...
https://www.m4carbine.net/attachment.php?attachmentid=10070
mine...
https://lh4.googleusercontent.com/-Bbju0xfnJlY/TqQNCRU2_xI/AAAAAAAAJEE/pLNPM82EGoc/s720/DSC02630.JPG
-Matt
I gotta say, that ^ certainly looks to be the case
roadDOG.19
10-23-11, 16:38
Good pic Matt, thanks. The divot and through hole are actually the same size, I can start a 1/16" bit in them. Looks like I will be picking up a new pivot pin and going from there.
Thanks to everyone, appreciate the input.
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