Beeman QB79/AR2079-A HP Resurrection

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SpiralGroove

SpiralGroove

Member
Oct 20, 2020
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Washington, United States
Hey Guys,
Had some spare time, so I decided to work on my .22 cal. HP QB79/AR2079-A conversion.
It's had Tank Block/Transfer Port leaking problems since I can't remember .... likely 2018/2019. I think I'd gotten very tired of fixing air leaks ...........

She, her brother and second cousin haven't been shot shot for years. I think I still have parts for 4 QB's/AR's ..... valves, barrels and stocks etc. from 2014/2015.

Fixed the Tank Block leak, but when firing - she's still wasting air out the transfer port/action connection. I believe I set the HP air tank is set around 1300/1400 psi, currently getting around 880 fps with H&N 5.55. Tried Meisterkugeln's, but they were not very accurate.

Looking forward to shooter her again and may resurrect the relatives too:).

AR2079-A2.jpg


AR2079-A.jpg


QB79 HP Tune2 .jpg
 
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nervoustrig said:
Looking good, Kirk. Nice to see the QB platform getting a little love. Definitely played big role in my journey into airguns.
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Yeah Jason, I pretty much owe everything I did on the QB series to you and Bob Sterne(y):cool:.

I bought two AR2079A's back in 2018 for $100 each from Field Supply as Refurbished. Both have issues with TP/valve alignment and hence there's a larger opening to fill in the connection with the barrel. Trying to find a way to seal this - likely wasting 5%/10% of my air - it's mostly just annoying:cautious:.

I still have a stock QB78 Delux and another QB79 laying around is parts - that need converting;).
 
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SpiralGroove said:
Both have issues with TP/valve alignment and hence there's a larger opening to fill in the connection with the barrel. Trying to find a way to seal this
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I don't suppose you have a picture of the misalignment?

There are few different approaches for dealing with it but I'm afraid I would just confuse things if I tried to describe each one, absent any knowledge of the severity of the misalignment, whether the opening in the air tube has already been altered, etc.
 
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nervoustrig said:
I don't suppose you have a picture of the misalignment?

There are few different approaches for dealing with it but I'm afraid I would just confuse things if I tried to describe each one, absent any knowledge of the severity of the misalignment, whether the opening in the air tube has already been altered, etc.
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I'll take apart a different AR2079 tomorrow or Sunday to give you a pic. As I remember, the valve was aligned too far forward and didn't allow a shelf for plastic tubing or o-ring to sit into. So now, we almost need a doughnut like rubber piece that would seal both surfaces together - outside of the larger OEM hole.

Unfortunately, IMO .... the two curved, mating surfaces aren't wide enough to apply the required pressure to seal this larger area.
 
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SpiralGroove said:
I'll likely need help from Jason .... I've developed a sort of mental block - for fixing these guns.
I need Dr. Nervous-Trigger .....................
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Jason is outstanding when it comes to fixing PCP's! Oh...he has chimed in...it will get done soon! Yeah...we all get mental blocks when it comes to servicing PCP's....more thoughts on it the better!
 
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Okay, with the exhaust port biased forward, the good news is it's probably the easiest form of misalignment to remedy. Assuming you need it to come back no more than 0.020" - 0.030", simply remove a bit of material from the head of the valve retention screw so the valve can move back a bit further. It sacrifices nothing in terms of safety because the shear load and bending moment is carried by the threaded shank, not the head. Plus the steel backer block is there if the screw were to fail.

By the way, most guns will have a gap between the valve and backer block so I like to add shim stock so the backer block is taking the load. I don't like that single valve retention screw, especially in an HPA application at a pressure well above that of CO2. In this case, it may be that fixing the alignment will allow them to contact naturally but check it with a dry fit. The way I evaluate the fit is by inserting what I think is a shim too thick, and watch what happens when I fully thread the stock retention stud into the backer block. If I can see it nudge the valve's exhaust port forward ever so slightly, I know it's about right.

The way I make shim washers is with a set of hollow punches. The stock is any of a variety of scrap material. An aluminum soda can is 0.004" - 0.005". Plastic blister packaging is good for finding varieties of thicknesses anywhere from 0.005" - 0.025" or so. Plastic containers for sour cream, whipped topping, etc. are another good source. Lacking hollow punches, all these materials can also be cut with common scissors and/or a hobby (Xacto) knife.

I hope this helps. If I'm missing some important detail or factor, just let me know and I'll see if I can help steer you in the right direction.
 
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nervoustrig said:
By the way, most guns will have a gap between the valve and backer block so I like to add shim stock so the backer block is taking the load. I don't like that single valve retention screw, especially in an HPA application at a pressure well above that of CO2. In this case, it may be that fixing the alignment will allow them to contact naturally but check it with a dry fit. The way I evaluate the fit is by inserting what I think is a shim too thick, and watch what happens when I fully thread the stock retention stud into the backer block. If I can see it nudge the valve's exhaust port forward ever so slightly, I know it's about right.

I hope this helps. If I'm missing some important detail or factor, just let me know and I'll see if I can help steer you in the right direction.
Click to expand...
Jason, believe it or not IIRC, I've already tried this and was able to move the valve backwards a little. Wasn't worried about the valve coming rearward, but I didn't shim it - or I was already at the rear backer block. I will check.

Also, I believe I added some JB Weld the the valve bodies, export path to give it more of a ledge/shelf. After this failed to stop the 5/10% blow back, and using multiple joint gaskets/o-rings, I got pizzed and haven't shot the guns until recently.

I've been so caught up in shooting/tuning my 3 RAWs I haven't given the mess much further thought.
I'll have to admit. these guns are very crude in comparison requiring much time is spent to fix their basic flaws.

I will crack things open today/tomorrow and get a fresh look:unsure:.
In the mean time both (.177/.22) AR2079-A airguns are pretty accurate preferring JSB 10.34's and H&N 5.55's.
 
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