79G won't hold air from handle ?



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Offline cbinfl

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79G won't hold air from handle ?
« on: August 01, 2017, 01:49:11 PM »
For background, I bought this gun in 1972 and it has worked great since then, until an hour ago !  Went to shoot and it was empty of air.  I was shooting on Sunday and all was well. Since new it has held air often for months at time.  Put a new cartridge in, smacked the butt and all the air came out the plunger in the butt. Wiped everything down and tried again and all the air came out the handle butt again.  Seems like the plug is not screwing in all the way.  There's about a 1/8" gap, but there always has been, I think ?  Without a cartridge the plunger cap screws all the way in flush with the handle.  Air seems to be coming from the plunger.  Wasted 4 cartridges, so I thought I'd ask the experts.  Also a recommendation for a good rebuild guy, if that becomes necessary.

Many thanks for any advise or suggestions.

Charlie
  • Clearwater, Florida

Offline the fuse

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Re: 79G won't hold air from handle ?
« Reply #1 on: August 01, 2017, 02:09:40 PM »
There are actually two orings that seal the piercing cap. One big one that is obvious and on little one that seals off the piercing pin as it moves back and forth in there. Either could be your culprit and neither requires special tools or much know how to replace.  Below is a link to how it's done. BTW You own a 45 year old Co2 pistol that has never been resealed. Wow!!
http://anotherairgunblog.blogspot.com/2011/07/simple-fix-for-leaking-s-78g-piercing.html
  • Carmel, NY
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Offline cbinfl

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Re: 79G won't hold air from handle ?
« Reply #2 on: August 01, 2017, 02:29:34 PM »
Thanks for the quick reply.  I'll study that link and order a set of seals tonight.  Here's a photo of the SW.  It was a Christmas present to me in '72.  $29.95 if I remember right.  Gotta sign off for now.  Again thanks.
  • Clearwater, Florida

Offline cbinfl

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Re: 79G won't hold air from handle ?
« Reply #3 on: August 01, 2017, 09:18:26 PM »
Went around this afternoon, Ace hardware, Home Depot.  Found some O rings that looked good, 1/4" x1/8" x 1/16" and a 3/4"x 9/16" x3/32" material unknown,   Leaking slower, and not out the butt cap, but still leaking. I can get 3-4 shots before empty.  They first 1-2 sound fairly strong. I wondered abut how tight for the small slotted nut ?   Might be time for a full rebuild.  I find 3 sources for kits;  Baker airguns,    Dan Kueng,  doesn't include a valve, O rings only, but half price,  and  MAC 1 but the kit is out of stock.

Let me say, I simply shoot paper targets at home.  I've always been happy with the power of the gun and often shoot at low power / 5 meter targets, so high power kits are not necessary. The kits that include a new valve all mention higher power. I really just want the gun repaired and another 40+ years of use.  Ha Ha. 

Any suggestions about repair services or the kits above would be appreciated. 
  • Clearwater, Florida

Offline the fuse

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Re: 79G won't hold air from handle ?
« Reply #4 on: August 02, 2017, 11:19:09 AM »
After 45 years of good service, it is time for a complete reseal. Or you will fix one thing and another will start to leak next month. If you want it cheap and cheerful, buy only the valve stem. You can get one from Dennis Baker or from John at JG airguns or from Allen at AB airguns. I'm sure there are others but they are who I have always worked with. Whenever I can, I send them my bad valve stem and they send me a rebuilt one. Sort of a trade in. Cheaper that way. You will probably be able to get away with cheapo orings inside the gun. They are probably made of buna or viton. Both expand when exposed to Co2. That's OK inside the valve area. Expansion will help the seal. The big oring that seals the piercing cap wants to be 90 urethane or every time you go to replace a Co2 cart, you will find an oring there that's five times as big as it should be. I buy all my orings in bulk from a quality online source. If I were you, I'd go to your local paintball game center. They will have most if not all the orings that you will need. Paintball guns and airguns are sort of similar. The 78G is a very easy gun to work on. The same blog site I gave you for the piercing cap reseal has  complete reseal tutorial for the 78/79G pistol. Probably more than one.
Good luck
  • Carmel, NY
I've got a touch of hangover, bureaucrat. Don't push me.
Rifles
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Offline cbinfl

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Re: 79G won't hold air from handle ?
« Reply #5 on: August 02, 2017, 12:16:30 PM »
Fuse,  Thanks for the info.  Last night I checked MAC 1 about 8 o'clock and the SW sets were listed in stock, so I placed an order.  Good to know about the other sources. I'll see how it goes, and report back.  I still wonder how tight to make that slotted screw on the puncture pin ? Seems it would need to be pretty snug ?

Thanks again for the help,  Charlie
  • Clearwater, Florida

Offline the fuse

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Re: 79G won't hold air from handle ?
« Reply #6 on: August 02, 2017, 02:11:30 PM »
Never more than hand tight on any airgun fitting. Good luck.
  • Carmel, NY
I've got a touch of hangover, bureaucrat. Don't push me.
Rifles
Crosman 160, 180, Model 1
Daisy 822, 922
QB57
Pistols
Smith & wesson 78G
Crosman 38T, Mark I, SA6
Daisy 722, 717, 1200, 118

Offline cbinfl

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Re: 79G won't hold air from handle ?
« Reply #7 on: August 05, 2017, 10:46:32 PM »
Just an update for anyone interested.  I received the kit fro MAC 1 today, and just finished getting it back together.  A few false starts, but I've no extra pieces so I guess we're ready to go tomorrow. I wonder about the mention of heating up the gun, in the MAC website description, before pressurizing it ?  I can leave it in the sun here in sunny Florida for an hour or so?  It's 90'+ every day lately. Any advise is welcome. 

Charlie
  • Clearwater, Florida

Offline the fuse

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Re: 79G won't hold air from handle ?
« Reply #8 on: August 06, 2017, 04:13:55 PM »
Heat makes the seal on the valve stem more pliable so it makes a nice nesting mate with the valve........I think. Sitting in the Florida sun should do it. Don't want to melt it. I'm curious about the Mac kit. Do you have a chroney?
  • Carmel, NY
I've got a touch of hangover, bureaucrat. Don't push me.
Rifles
Crosman 160, 180, Model 1
Daisy 822, 922
QB57
Pistols
Smith & wesson 78G
Crosman 38T, Mark I, SA6
Daisy 722, 717, 1200, 118

Offline cbinfl

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Re: 79G won't hold air from handle ?
« Reply #9 on: August 06, 2017, 04:52:38 PM »
OK, So I set it in the sun for about 15 min. Got nervous as it was hot to the touch. Put a cartridge in and success !  Put about 50 pellets through it, mostly on half power, and it's great.  Very loud on full power.  I've got the power screw at about midpoint.  Sorry no chrony. I think about getting one every once and awhile, but I'm a pretty casual shooter.  Any you recommend ?

Charlie
  • Clearwater, Florida

Offline the fuse

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Re: 79G won't hold air from handle ?
« Reply #10 on: August 07, 2017, 08:29:00 PM »
I am a casual shooter as well but I do all my own work and tinker a bit here and there. I want to know whether what i'm doing is improving the gun or not. And I want to know how a gun I buy is shooting compared to stock values. I therefore wanted a chrony and did not want to spend a fortune for one. I bought an F1 Shooting Chrony for bout $80. They cost a bit more now. There are cheaper ones. Do some shopping but for about one 100th of the cost of my guns I feel it's well worth having one.
  • Carmel, NY
I've got a touch of hangover, bureaucrat. Don't push me.
Rifles
Crosman 160, 180, Model 1
Daisy 822, 922
QB57
Pistols
Smith & wesson 78G
Crosman 38T, Mark I, SA6
Daisy 722, 717, 1200, 118

Offline cbinfl

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Re: 79G won't hold air from handle ?
« Reply #11 on: August 08, 2017, 12:00:28 AM »
Fuse,  I appreciate all your info.  I'm very happy with the MAC 1 kit. Judging by sound the gun is definitely shooting stronger.  I have about 80 shoots on the first cartridge since yesterday, and it is holding air fine.   Except for 4-5 shots all have been at half power.  There are more shots to go on this cartridge, so shot count is fine.  Attached are two photos of the old valve piece.  It seems OK to me, but I installed the new one anyway.  There was a little rust on the spring inside the valve, but no replacement spring was in the kit, so I simply cleaned and oiled the old spring.  Hopefully it will be OK.
« Last Edit: August 08, 2017, 01:26:23 PM by cbinfl »
  • Clearwater, Florida

Offline the fuse

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Re: 79G won't hold air from handle ?
« Reply #12 on: August 08, 2017, 11:16:18 AM »
Yeah the old valve stem seal looks shot to me......or nearly so. If you shoot your 79g regularly and always put a couple drops of ATF or non-detergent motor oil on every cart. it should shoot well for decades. Have fun.
  • Carmel, NY
I've got a touch of hangover, bureaucrat. Don't push me.
Rifles
Crosman 160, 180, Model 1
Daisy 822, 922
QB57
Pistols
Smith & wesson 78G
Crosman 38T, Mark I, SA6
Daisy 722, 717, 1200, 118

GTA - What's been your success with air gun target practice?