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Author Topic: Possible "Tavor face" improvement that is free.  (Read 22737 times)
Gear Head
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« on: September 09, 2013, 10:55:02 PM »

While I had my gun all apart I have been taking the time to study how everything works that we don't see normally. One of the things I noticed was the end of the gas piston guide tube and its relationship to the ejection port cover notch. I have no idea what the actual IWI name is for the "piston guide tube" (PGT) but that is what I am calling it for now.

As many of you know, you can see a gap in the top center of the ejection port cover and gas comes out of there hitting you in the face giving you the condition known as Tavor face. If you look in these pictures you will see how the end of the PGT is right at that notch in the ejection port. The bolt carrier doesn't come all the way out of the PGT during operation but almost. Whatever gas doesn't get vented out the small hole in the gas block itself continues through the PGT into the receiver. Where it goes many directions including in your face.

Well I realized that gas is no longer needed to operate the bolt carrier by the time it reaches this point so if there was a way to vent it in a controllable direction outside the gun body that it would help. You can see in the pictures the bottom side of the PGT through the ejection port. It sticks back about 3/4" or so. I decided I would try drilling vent holes in it at an angle that would aim the gas directly at the open ejection port. In my case with a right hand gun, the right hand ejection port. This theory would work just as well on LH models out the other side.

I just did this today and don't have my gun back in order to test it but I don't see how that could hurt it any. Obviously drilling holes in your gun isn't to be taken lightly but I tend to dive right in to things like this. It is free provided you have a drill but you do have to pull your barrel to get this piece out so it is a little involved. The receiver doesn't have to come out though. This part is also where the IDF rear sight and magnifier mount is I think. So I think it would be possible to switch your flat top gun to an IDF model if you could source this part as well as the correct IDF front sight and short rail or sight to mount directly to the gas block. I know I would like those parts to be able to do this for part design anyway.

This shows the position of the bolt carrier when it is fully rearward. You can barely see the end of the guide rod/gas piston.


Here is the end of the PGT in the receiver.


Here is what it looks like through the ejection port.


Here is the side I modified for a RH gun. You can see the holes are pointed at the ejection port.


Here you can see how there is space above the holes when the piston is back allowing gas flow to exit freely instead of being pushed out the crack between the piston and end of the tube directing it more backwards into the receiver.


Finally, this is the small gas vent in the gas block that is supposed to vent the excess gas. It looks to be about 1/16" OD versus the diameter of the PGT which is over 5/8".


I don't expect any cycling problem since the vent is at the very end of the tube but I have certainly voided my warranty. Well I think I did that the day after I got my gun actually... Roll Eyes
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NWGlocker
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« Reply #1 on: September 09, 2013, 10:57:47 PM »

Great post, nice and detailed explanations!

You sure you don't want to call it "SAR face"?
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Paletiger
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« Reply #2 on: September 09, 2013, 11:21:08 PM »

Let us know how it functions when you get her all back together;)
Nice work
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Gear Head
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« Reply #3 on: September 09, 2013, 11:24:30 PM »

Great post, nice and detailed explanations!

You sure you don't want to call it "SAR face"?

SAR face is a bit easier to say I guess. I didn't name it Tavor face though. I'm not sure where it was first referenced. Maybe Judo's thread.

It will be about a week and a half before I get to shoot it still.
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Rangerone
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« Reply #4 on: September 10, 2013, 06:17:28 AM »

This is an interesting approach.  Will you be able to test it with and without a suppressor to see how much it vents?  How will you monitor the venting out the ejection port?

Keep up the mods!
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Gear Head
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« Reply #5 on: September 10, 2013, 10:48:35 AM »

This is an interesting approach.  Will you be able to test it with and without a suppressor to see how much it vents?  How will you monitor the venting out the ejection port?

Keep up the mods!

I will be able to test it with a suppressor. I'm not sure how I will be able to measure tho beside knowing that I don't have teary eyes after a mag dump. Lol
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pretorian
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« Reply #6 on: September 10, 2013, 11:32:14 AM »

Hmmm...Interesting....
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Rangerone
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« Reply #7 on: September 10, 2013, 07:29:58 PM »


I will be able to test it with a suppressor. I'm not sure how I will be able to measure tho beside knowing that I don't have teary eyes after a mag dump. Lol


Maybe a "Range Buddy" can observe or a camera setup... The lack of teary eyes would also work!!!

Hope it works well!
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GaJoe1950
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« Reply #8 on: September 10, 2013, 10:01:41 PM »

Gear Head, I noticed Sugru mentioned in the dented brass thread. I wonder if a thin layer of Sugru under the flange of your Flex swivel (apply to flange, install swivel and trim excess after curing) could act as a gasket to prevent "Tavor Face"?
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genStrat
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« Reply #9 on: September 10, 2013, 10:05:49 PM »

Gear Head, I noticed Sugru mentioned in the dented brass thread. I wonder if a thin layer of Sugru under the flange of your Flex swivel (apply to flange, install swivel and trim excess after curing) could act as a gasket to prevent "Tavor Face"?

I used Sugru on my deflector. It seems to have good resilience in that location, but its not under constant pressure; i.e. serving as a gasket. I haven't seen anything to suggest it would hold up or just conform.
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Gear Head
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« Reply #10 on: September 10, 2013, 10:13:53 PM »

Gear Head, I noticed Sugru mentioned in the dented brass thread. I wonder if a thin layer of Sugru under the flange of your Flex swivel (apply to flange, install swivel and trim excess after curing) could act as a gasket to prevent "Tavor Face"?

I believe that with the revised design that there may not be a need for anything but there is a flange there that could be used that way.
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NoShelter
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« Reply #11 on: September 10, 2013, 10:27:16 PM »

I'm looking forward to seeing the results.

My concern here would the possibility of carbon entering the chamber area and fouling up the works.
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Gear Head
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« Reply #12 on: September 10, 2013, 10:39:01 PM »

All the gas is already entering the receiver but being blown back in a radial fashion all over. I am just trying to direct it out of the gun instead of being blown into it.

It would be the same volume of gas as I have not done anything to the gas block to change the amount. I'm just trying to change the direction it goes.
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NoShelter
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« Reply #13 on: September 10, 2013, 11:02:29 PM »

It's my (very limited) understanding that some of the gas is expelled during the forward motion of the piston also. It seems like this mod would expel it out of the new ports.

Wouldn't mean that a side-effect of directing the excess gas from the new ports would also mean that more overall gas is coming out?

I'm looking forward to seeing more info!

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Gear Head
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« Reply #14 on: September 10, 2013, 11:43:36 PM »

No.

Gas only comes out when the round is being fired. That is the gas that the gun uses to cycle. When the bolt is returning forward, The gas pressure has dropped off and only residual gas remains. It wouldn't be pushed back into the barrel because the restriction for that is too great. So it would get squeezed out from around the piston and into the receiver. In my case now, it would go out the holes. But it is the same amount of gas either way.
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« Reply #15 on: September 11, 2013, 12:51:28 AM »

GH,   One question on the topic.  As the system sits stock, if you submerge the gun in shallow water and pull it up and fire, the gas system would seem to stay for the most part dry, because there is no pressure to force the air out even though it's submerged.  If you open up the cylinder and submerge it, I am thinking all the air will be forced out due to the size of the openings to the piston cylinder.  If the cylinder is now full of water and all of it does not drain out when you pull it out to fire it, any chance of a water cylinder lock up, the same as in an engine cylinder when you pop a head gasket?  Or can you guarantee it will drain out  fast enough to fire safely?  Just a thought?  It may be the reason for the small gas port opening to release the gas and looking at mine there seems to be a close enough tolerance between the piston and cylinder to keep the water out if the pressure is not to high, or water is not to deep. 2 cents
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NoShelter
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« Reply #16 on: September 11, 2013, 08:01:30 PM »

No.

Gas only comes out when the round is being fired. That is the gas that the gun uses to cycle. When the bolt is returning forward, The gas pressure has dropped off and only residual gas remains. It wouldn't be pushed back into the barrel because the restriction for that is too great. So it would get squeezed out from around the piston and into the receiver. In my case now, it would go out the holes. But it is the same amount of gas either way.

Thanks for that info. I learn somethin new every day Smiley
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Gear Head
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« Reply #17 on: September 11, 2013, 11:28:54 PM »

GH,   One question on the topic.  As the system sits stock, if you submerge the gun in shallow water and pull it up and fire, the gas system would seem to stay for the most part dry, because there is no pressure to force the air out even though it's submerged.  If you open up the cylinder and submerge it, I am thinking all the air will be forced out due to the size of the openings to the piston cylinder.  If the cylinder is now full of water and all of it does not drain out when you pull it out to fire it, any chance of a water cylinder lock up, the same as in an engine cylinder when you pop a head gasket?  Or can you guarantee it will drain out  fast enough to fire safely?  Just a thought?  It may be the reason for the small gas port opening to release the gas and looking at mine there seems to be a close enough tolerance between the piston and cylinder to keep the water out if the pressure is not to high, or water is not to deep. 2 cents

First of all, I am not guaranteeing anything. Heck I haven't even been able to get my gun back together yet to see how it is effected by this if any.

I have no idea about how it will work after being submerged. Either bone stock or with these holes in it. But theoretically, water will find it's way into everywhere. Draining it out faster would be an advantage in your case.

I did a quick search and couldn't find an article I'm pretty sure I read and didn't make up. It talked about amphibious soldiers drilling drain holes in their gun so water ran out faster. The most important thing to drain is the barrel. That is where the bullet would act as the piston in your engine example and explode the barrel.
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Rangerone
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« Reply #18 on: October 06, 2013, 04:27:05 PM »

Hey GH:

Any updates on how the "vent holes" working out for directed gas venting?
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Gear Head
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« Reply #19 on: October 06, 2013, 05:10:32 PM »

I have only been able to fire a handful of rounds since I did this. Not enough to know how well it works. But the gun had no issues cycling.
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