Gas Tube Blowout

[markeb]

Looking for advice...

Some years ago I built a special purpose FAL. 16.25" barrel, out of a beater G1 kit and some odds and ends on a coonan receiver. The idea was to make a pig hunting rifle that would be quick in dense woods.

Anyway, the first time I fired it, the gas tube blew back. After a bit of gnashing of teeth and close inspection, it became apparent that the threads in the gas block don't have enough bite to hold the tube in place.

As I understand my options, I can attempt to silver solder a short tube in place, or replace the gas block, or do something radical (as yet unknown).

I've tried replacing the gas tube with a "new" imbel tube, same result. The piston works freely and properly, the barrel is properly timed.

Any advice on the best path forward would be appreciated.

[bookertbab]

Solder the tube in.

[markeb]

Any advice on how to clean the gas block so the solder will flow in there and stick? I've not had a lot of success with silver solder in the past.

[gunplumber]

this is common on the worn-out, corroded G1 gas blocks. sandblast, solder, then cut the tube to a short one.

[markeb]

Ok, thanks. I'll give it a try. Given my skill at screwing things up, I may be back....:-)

[KY FAL Guy]

Just for future reference, (because I may have to do the same thing) why would you want to cut the tube to a short one after soldering? I'm having the same problem now, and I just ordered a new tube thinking that might repair it. If it doesn't, I will follow this same route.

[gunplumber]

I suppose if you never need to remove the rear gas tube support or gas regulator, you could leave it full length, but since a soldered tube can't be unscrewed, you need to shorten it to disassemble the components, or (as on the original model) unbreech the barrel 30 degrees (you don't want to do that . . .)

[KY FAL Guy]

I guess if wouldn't really affect anything. The gas would already have passed the piston head. Probably only have more carbon in the handguards.

[W.E.G.]

Originally posted by ratas calientes at http://www.falfiles.com/forums/showt...900#post482900
On my G-1 build, I had a leaky gas tube, so I decided to make it a "shorty" tube by soldering it into place and cutting it down in length. This is my experience:

On my first attempt, I cleaned the mating parts with turpentine then alcohol. I put on a generous amount of silver solder paste, then I heated it up with MAPP gas till it was good and red. After it cooled, I cut if off to the correct length (which I derived from inspection of my STG-58A). This was somewhere on the order of 4.25 inches? I can check if you like. I took it to the desert and fired about 100 rounds through it. After I got it home, I inspected the gas tube, and it was loose - the solder never did hold. It was easily removed by hand after removing the pin.

This is what I now recommend to anyone who wants a good, strong, permanently soldered short gas tube:

Required supplies:
MAPP gas
silver solder paste
silver stick solder (~1150 degree stuff)
flux for above

1) Use a wire wheel to remove all of the parkerizing/finish on the threads of the gas tube. You will also have to remove the finish about 1/4 inch beyond the threads. When the gas tube in screwed into the gas block, you want about 1/8-inch of bare metal still showing.

2) Use a sanding disk on a Dremel to remove the parkerizing/finish on the inside of the gas block between the gas block female threads and the opening of the gas tube hole. I cut some slots in the sanding disk to get it to fit into the hole.

3) I used a cheapo .50 caliber bore brush and an electric drill to remove the parkerizing/finish on the gas block female threads that mate with the gas block.

4) Remove the finish on the rear of the gas block, where the tube enters. This will allow for formation of a solder "fillet."

5) Clean mating parts in acetone. Scrub with your old toothbrush - and buy a new one for the bathroom.

6) Clean again with alcohol. Let dry.

5) You will then need some silder solder paste, silver stick solder (proper name?) (~1150 degree stuff), and the proper flux. I managed to borrow some from a friend in a machine shop. I used only about 2 inches of stick solder. I also mixed less than half a teaspoon of the flux.

5) Apply a generous amount of silver solder paste to the clean gas tube threads.

6) Apply flux to the remainder of the gas tube that has been cleaned and has had the finish removed.

7) Install onto receiver/barrel assembly, using the gas tube nut to maintain alignment. (This assumes NO gas regulator, spring, front sight parts, gas plug, etc.) Don't forget the little pin!

8) Clean the inside if the gas tube with alcohol to remove any solder paste that may have gotten inside.

9) Clean the gas vent.

10) IMPORTANT! Check that your gas piston slides FREELY with no binding. This is critical. Be sure to remove it. (My failure to check for free piston movement ended up with me re-heating the silly thing up three more times to get it aligned. I was not going to bend it into alignment. Another story . . . )

11) I placed the barrel assembly vertical in my vise, using a couple of wooden blocks to hold it. Rubber or plastic vise jaw protectors will probably melt or get damaged during heating.

12) Heat the gas block/gas tube interface area to a dull/medium red. Heat as evenly as you can, trying not to apply heat to the gas tube. When the solder flows, it will follow the heat. Apply/touch the solder stick opposite of the heat source. Be patient. It will flow into the gas tube joint quickly once it get hot enough. Once it flows in and a solder fillet is formed, continue to heat evenly on all sides to make sure that the solder paste melts and the stick solder slows completely into the upper part of the joint.

13) Let cool.

14) Check for free movement of the gas piston.

15) If some solder got into the inside of the gas tube, file it back carefully with a small round file. (I ended up with one small spot of solder.)

16) Clean up the joint and excess flux with hot water and your handy toothbrush. You will probably get some hardened flux on the gas regulatr threads. Just scrub it out.

17) Cut gas tube to the proper length. (~4.25 inches? Check this!) A Dremel with cut-off wheel works great. Clean up cut with file, etc. I also added a small interior chamfer with a brass chamfer tool.

18) If the gas block and/or gas tube are already parkerized they way you want, you can oil this finish up again, and it will look just fine.

19) Test fire.

If you have any detailed questions, let me have it. After trying stick solder, it is much better than the paste stuff for certain applications.

Ratas

[W.E.G.]

Only thing I'll add is, it seems you better your chances of soldering the tube in correct alignment if you solder it in place as a full length tube. That way the tube is supported in the rear during the whole process.

Then cut the tube short after you are sure everything is lined up just right.

[KY FAL Guy]

W.E.G., thanks for the good info. This will make doing this alot easier.

[[486]]

Originally posted by KY FAL Guy
I guess if wouldn't really affect anything. The gas would already have passed the piston head. Probably only have more carbon in the handguards.

It'd be just like the newer STG-58s, those have the shorter gas tubes...

[Pluribus]

My solution to a similar problem on an Imbel was to tin the threads on the gas tube.

http://www.falfiles.com/forums/showt...hlight=tinning

So far, so good too.

[KY FAL Guy]

So Pluribus, you haven't had any more problems since tinning? I will give this a try before I solder the tube in place. I would like to keep my G/T the way it is.

[Pluribus]

Originally posted by KY FAL Guy
So Pluribus, you haven't had any more problems since tinning? I will give this a try before I solder the tube in place. I would like to keep my G/T the way it is.

No, none. It may not be the fix-all, end-all for every blow by situation but, in my case it has held up fine for the 2200 or so rounds this rifle has had since. I'd think a person could just as easily use a hi-temp silver solder too.

[gunnut1]

Chances are that the threads in the gas block are fine. The gas block is much harder then the tube. Get a new tube and put it on and you should be fine. I have blown out 2 gas tubes and fised them simply by replacing the tubes.