TAU-7 repair?

[SPPcoach]

What exactly is "the next problem". I've spent about 10 years maintaining almost 20 Tau's for the college team I help coach.

Here's info on O-rings:

Tau-7 O-Rings.pdf

It now holds pressure when a 12 g CO2 cylinder is installed. The 15mm x 19mm x 2mm O-ring is the perfect fit for the CO2 cap. Hooray.
When i shot it a puff of white fluff came out the muzzle. I am guessing this was styrofoam from the pistol box. Now it won't fire again.
I am guessing that there is styrofoam jammed up in the trigger and valve. I am reluctant to disassemble her pistol without proper instructions and experience.

What college?

[SPPcoach]

Here's info on O-rings:

Tau-7 O-Rings.pdf

This is hugely helpful. Thank you!
You are with MIT? Will Hart was my NCDS pistol trainer in Iowa in 2012. We were just emailing earlier this month about our program. OMG this is a small world.

[Gwhite]

In general, I'm not allowed to mention the school in an on-line forum without clearing it with the lawyers. I had to add a lengthy disclaimer to some YouTube videos on cleaning Benelli .22's before I could post them openly. I see that you figured it out...

My statements are my personal opinions, and are not supported or endorsed by the college, obey all safety procedures, etc. etc.

[SPPcoach]

We are full in on 10M International air pistol.
Cardinal Center set up a temporary AP range at our Nationals last year. Vladimer came up, brought his electronic targets and Pardini pistols.

COLLEGIATE PISTOL COACHES SELECT SASP AS NATIONAL GOVERNING BODY
Written by Tom Davis on November 17, 2020.

The Scholastic Action Shooting Program (SASP) has been named the National Governing Body for Pistol by the NCAA coaches.

As the governing body, the SASP will facilitate the Pistol Championships being held March 24-27 at Fort Benning, GA. According to the National Rifle Association (NRA), college air gun competitions are practiced by over 300 collegiate teams across the nation. The NRA will be lending expertise and contributing as a main partner of this program. With SASP’s recent announcement of adding international air disciplines to their program, NCAA shooting programs will directly benefit from the addition of new youth SASP international athletes looking to continue their shooting career in college.

We have 3,000 kids in the pipeline and ~30 attended the J.O.'s last yoar in COS.
We are hiring a full-time DOD for the International position and will be adding matches to our calendar.
My team www.WildGats.com has been successful in action shooting with 34 athletes last year and are now starting precision air with one athlete.
Every journey starts with a single step . . .

[Gwhite]

The SASP folks and the NRA messed up the press release big time. The NCAA does not have (and never has had) anything to do with collegiate pistol. Until now, the International pistol program has been run by the NRA. The NRA competitions division furloughed the one person who had been managing collegiate pistol for many years, and they didn't know when they would be able to rehire anyone to fill the void.

Although most college teams & ranges are still shut down, we are hoping to salvage at least some sort of season. With any luck, we are going to try to hold the Collegiate (International-Style) National Championships at Fort Benning at the end of March. The collegiate coaches have been having lots of Zoom meetings to try to sort all this out, and SASP sounded like a really good place to land.

One big question is when schools will open up again (& how much) for the second semester, and whether anyone will be able to travel by the end of March without lengthy quarantine restrictions.

[SPPcoach]

The SASP folks and the NRA messed up the press release big time.

Yup. Someone got tripped up on the title of that PR. I mildly edited the official release to try to get the semantics accurate

One big question is when schools will open up again (& how much) for the second semester, and whether anyone will be able to travel by the end of March without lengthy quarantine restrictions.

I dont have good news from Arizona. My college PAC is planning on continuing "4-mode teaching" until 2022. That is code for no in-person learning.
Our 'clubs and associations' has also stated 'no travel' for clubs. So that means no Nationals for us.

[SPPcoach]

What exactly is "the next problem".

I cocked it before installing the CO2.
Now when I install a new 12 g CO2 cylinder it blows the CO2 out the action. I am experimenting so I left a pellet in the chamber. It does NOT blow the pellet out.
What am I missing?

[Gwhite]

OK, it sounds like the firing valve is stuck open. I would still expect it to push a pellet out, unless one or both of the breech seals is missing. Any idea where the gas is coming out? "The action" has several places that it could be venting, depending on what is wrong. It's also possible the seal at the back for the access screw that closes up the firing valve/seal area has blown out.

If you look into the slot at the rear of the "hammer" with it cocked, you should see the end of a round metal pin about 3 mm in diameter sticking forward just enough so the hammer can whack it. That's the front end of the firing valve. With no CO2 in the pistol, it's spring loaded, and you should be able to reach in with a toothpick & move it back. It should spring forward when you release it. If you don't see the pin, it's probably stuck back.

It's not a very complex mechanism. There's no regulator to deal with. The hammer taps the firing valve hard enough to pop it open briefly, after which the gas pressure should close it again.

[bdutton]

http://www.74fdc.files.wordpress.com/20 ... ploded.jpg

This is a big help! Any chance you have the link to the parts list to go along with this diagram?

Sorry I don't.

[pbrejsa]

Dear folks
Czechoslovak pistols TAU7 (previously also TAU5, TAU6) began to be produced in the 70s of last century. It is therefore more than 40 years old and is still produced today, maybe. At that time, they used the most accessible and most common o-steps on the local market, which could be bought in all household necessities and plumbing, because they were in the water valves in every household. Little did anyone know that you would ever go abroad. The dimensions are in the metric system and the rings were measured according to the outer diameter and the cross-sectional diameter, which was always 2.3 mm. All pistols had to have 2 plugs, which were exchanged when replacing the CO2 bomb. Domestic sports shooters more often used a permanent refill plug with a valve, through which CO2 could be refilled continuously from an external 200 gram bomb. The dimensions of the threads on the plug are also metric, I guess M20x2, and allowed refilling from conventional fire extinguishers with a charge of 5 to 6 kilograms. I don't know the dimensions of the o-rings of the current provenance. Sorry.
Another situation was around the firing valve. At that time, only 2 plastic materials Teflon a and the Czech version of polyamide Silon were available. Both of these plastic materials have some insufficient properties for a given application. High-pressure polyethylene (eg Chirulene) proved to be the best for repairs that should withstand long-term and if the seals and the internal space are not dirty and damaged by unprofessional assembly. It is used, for example, as a material in surgical joint replacements. It is not cheap but will serve in a pistol for many years. When repairing, you need a skilled lathe turner and gunsmith.
Maybe TAU7s will shoot for many years, they are simple and easy-to-maintain pistols that are not of interest to today's hectic times. Excuse my longer post and keep it cool.
Petr
P.S. excuse my rough English and google translation

[Gwhite]

Here's a parts list I extracted from a manual:

Match Tau-7 Parts List.pdf

(89.44 KiB) Downloaded 352 times

Before I could get replacements from BRNO, I made my own firing seals out of nylon. The seals are a very tight press fit in the frame, and mine were a little smaller than the factory ones, but they worked OK. The latest design of firing valve has a plastic face on the valve sealing area, which eliminates the corrosion problem that killed valves in the past.

[SPPcoach]

Any idea where the gas is coming out?

I am going to pay attention to that next time I put a CO2 into it.
Now that I have taken it apart a few times I have a better understanding of the mechanics of it, and where it could be leaking.

OK, it sounds like the firing valve is stuck open.

I have had it out a couple of times now. It is somewhat crude machining except for the seat for the seal. It does not have any burrs and moves freely.
The spring is in tact with no collapsed coils and both pigtails are properly shaped.

It's also possible the seal at the back for the access screw that closes up the firing valve/seal area has blown out.

I think the rest of the O-rings are OK. They don't have any visible cracks and feel plyable to the touch. I haven't taken them out since I dont have replacements on hand. That may be needed next after I insert the next CO2. I guess they don't take the abuse that the CO2 cap has to endure.

If you look into the slot at the rear of the "hammer" with it cocked, you should see the end of a round metal pin about 3 mm in diameter sticking forward just enough so the hammer can whack it. That's the front end of the firing valve.

That took me a while to understand but OK.
On hers, the firing valve is not nearly long enough to do that.
In the picture, I lined the BACK of the valve up with where it seats.
The front does not extend far enough to get hit by the hammer.
Hmmm.
https://www.dropbox.com/s/qm9udmwujdkk4 ... 9.jpg?dl=0
Still, the leaking is the first problem to resolve.
I think I am going to put an air hose to it in a few places and confirm i have a seal. I hate wasting those CO2 cylinders.

Is it OK to dry-fire this 'empty' without a CO2 in place?
Is it OK to dry fire this with a 12g CO2 in it but no pellet?

It's not a very complex mechanism. There's no regulator to deal with. The hammer taps the firing valve hard enough to pop it open briefly, after which the gas pressure should close it again.

It is brilliant in its simplicity and not nearly as bad as I feared at first.

[Gwhite]

That took me a while to understand but OK.
On hers, the firing valve is not nearly long enough to do that.
In the picture, I lined the BACK of the valve up with where it seats.
The front does not extend far enough to get hit by the hammer.
Hmmm.
https://www.dropbox.com/s/qm9udmwujdkk4 ... 9.jpg?dl=0

That's weird. That may be the problem. it sounds like something is preventing the valve from going far enough forward to seat against the seal. The little turned down section should be visible in the slot the hammer rides in . The rear face of the hammer is flat, and should be able to hit the end of the valve. Something isn't right.

You can dry fire it with or without a cartridge without much concern. In order to allow shooters to dry fire before a match with CO2 in the pistol, I developed a dry fire adapter.

viewtopic.php?f=4&t=33509&p=166476

The notch in the back of the adapter fits over the end of the firing valve, which shows you how much further forward it needs to go. If your original suspicion about white stuff coming out was indeed styrofoam from the box, there may still be a piece buried in the guts someplace. You should be able to look in the back and see daylight with the hammer cocked, as well as light coming down vertically from the firing port.

[SPPcoach]

You should be able to look in the back and see daylight with the hammer cocked, as well as light coming down vertically from the firing port.

I can see daylight. :-)

That's weird. That may be the problem. it sounds like something is preventing the valve from going far enough forward to seat against the seal. The little turned down section should be visible in the slot the hammer rides in . The rear face of the hammer is flat, and should be able to hit the end of the valve. Something isn't right.

Hoorah. You are spot on!

https://www.dropbox.com/s/2cs10jqcawzol ... 2.jpg?dl=0
https://www.dropbox.com/s/2cs10jqcawz ... jpg?dl=0
The valve was hanging up on re-assembly and held back 0.600" so it couldn't seat against the seal. There is a little machined step in there that was hanging up the valve.
Back in business. Thank you!

[Gwhite]

Glad to help! They really are excellent pistols. When they first came out (~ 1980?), the college team I help coach bought quite a few. The women's team won the Collegiate National Championship with a couple of them.

[SPPcoach]

Out of curiosity, what model pistol is most popular on your team today?

[Gwhite]

We have 26 Hammerli AP20's that we get students started on. From there, they typically get Hammerli 480K's that have been converted to use the AP40 cylinders. After that, they get issued either Benelli Kite's, Morini 162EI's or Steyr LP10's. We have a bunch of Kite Juniors that are suitable for smaller shooters. Some of the selection for more advanced shooters is a function of the grips we have available.

Our biggest problem at the moment (besides COVID 19) is that the several of the Hammerli 480Ks & Kites have died, and the only US service for them vanished when Larry Carter passed away.

[lalka686]

Sorry I'm late to discussion,
I love my Tau-7 and can state from experience that is as good as Pardini K60 or Pardini K12.
It was my first air (CO2) pistol & the only problem is the CO2 to be used at winter air or nationals.
I believe the barrels were made by Walther in Germany for Tau Brno. One of my uncle's first job back in 60's was making rifle barrels in CZ Brno.
Here is my homemade dry fire device for my Tau made out of paper clips & 2 steel 1/8" squares soldered together. The clip wire has a spring action & it takes two fingers to squeeze, install & uninstall while you hold back the hammer or while pistol is cocked.
I also made my own powerlet piercing cap that was missing,, barrel weights & compensators one from steel & one aluminum to act as additional weight.
After one year of getting used to pistol shooting, I took a shot at my first winter airgun with the Tau (2015 or 2016) I shot 559 while people laughed at me that I'm missing the air cylinder under barrel. I was the only one with Tau or CO2.
Bernard

[SPPcoach]

What exactly is "the next problem". I've spent about 10 years maintaining almost 20 Tau's for the college team I help coach.

She shot a new personal best on Wednesday. She is getting used to the procedures for managing her Tau7.
A 'new to me problem' is the proper procedure to change CO2 cartridges. We removed the partially-full cartridge to install a new one right before the match. I unscrewed the cap and it blew out the excess CO2 thru the grip and in the process kicked out the cap O-ring out of the groove. We will switch caps anyway, but now we can't use that cap again until we take it apart and re-seat the O-ring. :-(
Mid-match she felt it losing pressure. Whoops, that is my fault,
I didn't cock the pistol before tightening the CO2 cap, so it lost some gas. It was dropping shots by two scoring rings and sounded different so she wants to change CO2 cartridges. I dont want to loose another O-ring when changing CO2 again because then the gun will be inoperative. I have her 'fire' her remaining CO2 at the target. It is a casual shoot so no one is bothered (I know she can't do this during a ISSF match). There were only 4-5 shots from when the Tau went from 'pfffffft' to 'pfft' to 'click.' So it is definitely out of CO2. BUT when we unscrew the CO2 cap, it released a LOT of CO2 again.
What the heck?
At least time it didn't blow out the O-ring
I put the cap in my pocket for a few minutes to warm it back up before re-using it, because we can't swap it this time. :-(
1. How do you change CO2 when you have a partial charge without blowing the O-ring out of the groove?
2. How can you de-gas the pistol during an ISSF match when all air discharges count as a shot?
3. How can the Tau 'click' when the trigger is pulled and still have pressure in the cartridge?

[Gwhite]

If you "dry fire" a bunch in quick succession, the valve may have frozen, and couldn't dump the last of the CO2.

If you need to empty the pistol, especially when the CO2 is low, take it off the line, preferably outside or someplace where it won't freak out the other shooters. Wear ear protection if you are in an enclosed space. Open the loading gate and flip the pistol upside down. With the pistol uncocked, pull the cocking ears firmly to the rear. This will open the firing valve, and dumps the CO2 pretty quickly.

The reason they want you to alternate fill caps is that CO2 gets absorbed by the O-ring material. If the pistol has been left with CO2 for some time, there can be enough absorbed to form gas bubbles in the O-ring. This will expand it, making it hard to re-seat the fill adapter without pinching or shredding the O-ring. Over time, the bubbles will slowly chew up the O-ring. If you just used that fill adapter at the start of the match, it probably didn't have time to soak up much CO2, so you got away with it. When you alternate fill caps, the one not in use has time for the CO2 to dissipate, and the O-ring will return to it's normal size. Silicone grease (SuperLube) on the O-ring can educe the amount of CO2 absorbed.

This is a big advantage of using the small CO2 fill tank. The grip holds more CO2 when there is no space taken up with a cartridge, and you never remove the fill adapter unless it needs servicing. It's usually not practical for one pistol, but with a team using over a dozen, we had a 20 pound CO2 tank we used to fill the smaller "bottles".