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Old May 11, 2019, 18:34   #1
golfr
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How to replace an C1A1 gas block ?

I need to replace my gas block.The rifle won't cycle and and acts like it's starving for gas.I found out it is blowing a lot of gas on the underside of the block along the barrel seam. I know there is a pin and you have to remove the sling attachment along with the flash hider but my question is the block press fit to the barrel? Is it difficult to replace? After replacement, how does someone get the block aligned right again since there is a barrel gas port and sights involved?
Background, I have replaced the gas tube(stripped threads), plug, piston and spring. I did a masking tape test,the tube is fine but around the gas block seam, major blowout.I have an apex reconditioned gas block ordered that will be here by end of next week.Thanks

Last edited by golfr; May 11, 2019 at 19:25. Reason: bad spwelling
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Old May 11, 2019, 23:32   #2
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There's a gas block retaining pin that holds it in place on the barrel. You have to drive out the retaining pin from the right side as you are looking at the barrel from the top with the barrel muzzle facing forward from you , and drive it out towards the cocking handle side.

The retaining pin is tapered so it can only go in and out one way.

Getting the gas block lined up can be tricky, but I just go slow and line it up really close with using the front and rear sights. Others probably have a simpler method of doing it though.
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Old May 12, 2019, 06:40   #3
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Thanks for replying,I didn't want to proceed without some knowledge. I was surprised that there is little info on the web for removing the block.Only thing I was able to find was an animated youtube that showed the pin but that's it.
Still, how does the gas block align itself when it is reinstalled.Does the pin sit in a aligning groove on the barrel? Is there a procedure for getting it on straight? I was thinking a drift pin through the gas block port to barrel opening while setting the pin.Straight edge from front to rear sight may also help.
I am hoping this will fix the issue of not cycling.
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Old May 12, 2019, 15:06   #4
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Hello Golfr,

Please find attached 5 pages on the repairing gas blocks for FN C1A1 from the Canadian Forces Technical Orders. Good luck with your repair.









Attached Images
File Type: jpg Repairing gas block0001.jpg (106.3 KB, 83 views)
File Type: jpg Repairing gas block0002.jpg (68.2 KB, 81 views)
File Type: jpg Repairing gas block0003.jpg (77.6 KB, 80 views)
File Type: jpg Repairing gas block0004.jpg (111.6 KB, 78 views)
File Type: jpg Repairing gas block0005.jpg (86.9 KB, 78 views)
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Old May 12, 2019, 16:22   #5
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Where is it leaking at exactly? The "under side of the block along the barrel seam". Do you mean around the hole that the barrel presses into? If so, then you've got problems. Any way, when replacing a gas block, I use a press and two steel blocks that have a machined portion for the barrel to sit into. It's milled into a U shape that fits nicely around the barrel, but small than the gas block. This U shape is what I press against to remove the gas block. Once off, you can inspect to see why the gas is leaking in that spot. Also, while the gas block is off, I find a twist drill that fits perfectly in the barrel's gas port.

To put a gas block back on, I use a length of cut off shotgun barrel (fits perfectly). I eyeball line up to initially start pressing on the gas block. Then, as it gets close, I take it out and visually line it up so that the gas port in the barrel lines up with the center of the gas block. As I near the final press, I use an adjustable wrench to find center and turn it ever so slightly as it's being finished pressed into place. I have done it this way for over 25 years and it has worked for me.

I take the barrel out of the press and, using the appropriate sized twist drill, I put the bit in the gas block port and then see if it lines up with the port in the barrel. Most often, it's lined up, with only a few times that the gas block has needed tweaked ever so slightly left or right. And, I have found that the gas block hole is larger than the barrel's port. I also use this opportunity to look and see if the retaining pin's holes are aligned, too. Sometimes they need a little "adjustment". Put back together with retaining pin and test fire.

Leland
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Old May 12, 2019, 20:30   #6
golfr
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Thanks all for answers back. The area of the leak is the underbelly of the block that the barrel passes through.The leak is bad enough to split and blow out a gob of masking tape from the bottom of the block.
I kind of figured I was screwed with this block issue. I am a shade tree mechanic and I kind of thought this might be out of my realm of butchery. I do have a hydraulic jack and maybe a piece of pipe.It will all depend on if I can get the old one off and how tight of a press fit the new one is.
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Old May 13, 2019, 08:30   #7
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Can't get the block pin out,any suggestions. Bent a punch and damaged the block and it won't even budge.
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Old May 13, 2019, 11:04   #8
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Okay,it's off. Between beating with a 4lb hammer,drift pin and screw clamp (golf club head remover)and liberal amount of Krolls. Heated and beat the crap out of the block and not proud of it but it was worth it. The block is pretty mangled and wasn't easy. Don't try this at home, I am not a professional. Btw, the block is a type "B". I want to thank Airforce 1 for armorers info,it gave me ideas to get the part off.
Examining the block I was wrong.It looks like the gas was blowing out of the top of the barrel ring(not the gas tube ring,the barrel ring) instead of the bottom. There is a rust ring on the muzzle side of the block except for the top 1/4 quadrant of the barrel ring.The upper area has no carbon or rust ring and you can see the blow by. The area has that gray burnt powder look and is a good indicator of blow by and loss of gas pressure.
Next is waiting for parts shipment and pressing the new block back on.
I also noticed that the 4 allen screw flash hider used some kind of epoxy to help hold in place the screws and hider, any suggestions for a replacement adhesive.

Last edited by golfr; May 13, 2019 at 11:35.
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Old May 13, 2019, 15:08   #9
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Originally Posted by golfr View Post
I also noticed that the 4 allen screw flash hider used some kind of epoxy to help hold in place the screws and hider, any suggestions for a replacement adhesive.
9/16-24 thread works good or you could use green locktite (609)
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Old May 13, 2019, 15:53   #10
golfr
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I was thinking loctite but I Just ordered from Amazon some Permatex high temp thread locker. I may even use some on the gas block mount as a seal.
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Old May 13, 2019, 16:19   #11
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Originally Posted by golfr View Post
I want to thank Airforce 1 for armorers info,it gave me ideas to get the part off.
You are very welcome.
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