QB-79 help

[Splash]

I pulled my 79 apart this weekend to polish the internals. Well now I have a leak and can't find it, I've replaced the seals 3 times. What could I be missing? I did not enlarge any ports, just polished, cleaned, resealed and put back together.

[ribbonstone]

Got to trace down the leak first.  Are only three places it could leak from. Two can be found with one test.

With the bolt closed, dab soapy water at the muzzle and around the  end of the gas tube (where the gas block fits to the gas tube with two screws).  If it bubbles from the muzzle, then the valve stem is bad.  If it bubbles from the gas tube/paintball fitting joint, then those two o-rings need replacing (good news here is that the ones sold at k-mart for paintball tanks will work as replacements).

The 3rd place it could leak is from the o-ring around the middle of the valve, and that usually leaks backwards towards the trigger. Is a good bet that if the soapy water trick shows no leak at the muzzle or gas tube, then it's the valve's o-ring.


Unfortunately, when we work on these guns, have to be very careful to leave them super clean on the inisde...one bit of grit, a stray metal shaving, or some abrasive dust on the inside, and it's got a good chance of cutting the soft valve stem seal when it gets blown through the valve.

[Splash]

Thanks Rib, the last time I put it together I didn't hear a leak until I cocked the bolt. Then it was a steady hiss.

[ribbonstone]

Got four  choices:
Archer sells the whole valve...does not sell just the valve stem.

Mountain Air does who custom Delrin valve stems....but he's on vacation right about now.

Best Airguns does show just the valve stem being offered for sale....that's the part you want.
http://bestairgun.stores.yahoo.net/qbvastas.html

AB Airguns will rebuild valves...and can convert them to a differnt (stronger) type of valve stem...but he is real busy right now and only does the work on valves you send in.
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MR. Archer.  Would much prefer to deal with your company....but buying a whole valve when all you need is a valve stem isn't real cost effective (for the consumer).

[Splash]

Thanks again Rib. I didn't really modify anything, so it should be a seal issue. All I did was polish and remove the packing, from the old style valve.

[Stephen Archer]

There's one other thing I would try (if you haven't done this already). That's the "Pellgun Oil treatment".

Before buying anything, I would put a drop of Pellgun Oil into the gas hole in the tank block of the gun. Then connect the paintball tank and blank fire the gun 20 or 30 times. Next remove the paintball tank and leave the gun to stand for 24 hours. Now re-connect the tank and test for leaks again. If you still have a leak repeat these steps and wait another day. Test again. If you still have a leak, buy some parts!

I find that many "mysterious" leaks on these guns will self-heal with this treatment. If the leak is not too serious, this will often fix it. The Pellgun Oil swells the O rings and seals after it's blown through by the blank firing.

Normally, if the valve stem seal is leaking - and this is the likely culprit - you will be able to hear a slight hissing or "bubbling" sound with gas pressure "on" and the open breech held up to your ear. Often an examination of the face of the valve stem seal will show either pitting or dirt/debris when the valve is in pieces. Sometimes, the dirt/debris can be carefully removed and the valve will then work.

ribbonstone, thanks for your comment about our QB78 Valve Kits. Yes, I agree with you. Best Airguns had a good idea also sourcing valve stem assemblies only. I'll need to see if we can do this too...

Stephen Archer
Archer Airguns Inc.
http://www.archerairguns.com

[Splash]

Thanks Stephen, I'll give that a try. If it doesn't work I'll be ordering a valve and a few other goodies, from you.

[ribbonstone]

Am keeping 4 QB's running, so having a spare valve or two is fine by me (have already got them from you) and have gotten pretty good at making Delrin replacements.  So I can recommend having one complete functioning valve on hand...it's just easy to replace the whole thing and work on the busted one when you have time.

But if you could sourse just the stem, it would make people with one (or even two) QB's a lot happier.  The valve itself (other than the o-ring) is pretty hard to screw up unless you start polishing/grinding, so just the  valve stem would be a big help.
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BTW: Pushed the button (OK...did it by phone, but the same effect) on a 5mm 25" 15mm barrel blank.  Have two .22 QB's, one of which will become a .20...which will give me a .177, 20, 22, and .25.  Am thinking the converted QB78 (the oldest one of the four) would be the best candidate.'

This would be .22 /  .177 / .22 (bout the last .22 will become a .20)


And this .25 came late to class photos:

[Splash]

I replaced the valve and still got a leak. Soapy water on the muzzle, blows bubbles. I'm sure I voided the warranty on the new valve, cuz I opened it up, after it was still leaking and found a burr inside the valve. Can I polish out the burr and possibly get it to seal, or do I need to try another? TIA

[howie1a]

After seeing the problems you are having I am thinking of leaving my tf78 stock it seems to shoot fine sinice I shoot paper at 10 m I think maybe I'll leave it alone for now howie

[Splash]

Howie, I don't know what I did wrong, but I'll get it figured out, one day.

[Stephen Archer]

Hello Mike,

So I'm assuming the "Pellgun Oil treatment" didn't work for you with either valve???

If you purchased the replacement valve from Archer Airguns, please send me an email and indicate your order number. We sell many, many replacement QB78 valves with a very low rate of problems.

Stephen Archer
Archer Airguns Inc.
http://www.archerairguns.com

[Splash]

Stephen, I'm going to try the oil again, if it ever quits raining. I'll send you an email, with the # if it doesn't work. Thanks

[howie1a]

Splash you are very capeable if you have a problem I don't know if I want to go their . One of the problems is some of the discrfiptions of the mods give discriptions ( names) of parts that are not the same as the blow up plans of the rifle , and I think I will wait till I know the rifle better, It's a great rifle.howie PS where are you getting pel gun oil noe one in my area has it the only way I see to get it is on line I guess I have to add it to a order for some orther stuff or the shipping will make it like gold.

[Curioguy]

Mike, get her up and running soon and maybe we can do some trading. My ordering finger is starting to twitch and I don’t want to miss out on the summer sale that Archer Airguns is having on the QB79.