GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: Methuselah on March 14, 2024, 12:28:35 AM
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So far I'm thinking I'm outmatched. It was bought for the front stock to put it on a 1377, but I wanted to see if it was salvageable first, because, seemingly, I like pain and torture...
So first thing I did was misinterpret how the roll pin "fluff" came apart. I thought it the lighter colored end was the pin from other side, but turns out it was peened metal from the pin overextending through. So "fluff" probably destroyed. Perhaps it was sacrificial to begin with. Hopefully I'll post a pic so youze guys can see what I'm talking (rambling) about.
Blunder #2, Murphy is my bestist buddy. Like in the whole world even. Knocking out the roll pin, it had to fall 1" to the table. Nope, it left the planet, by now even Elon Musk would go bankrupt trying to catch up to it. It's just gone. Yeah, I know, plastic bag over it, right.
Perhaps blunder #3, I "fumbled" the valve coming out of the tube, and of course it spun. Oh man it spun, you would have thought it was a gyroscope. So no idea orientation to put it back, or which way the (threaded) hole points. Hi again Murphy.
Last part to disassemble is gonna be the valve. Man I really tried. Curved jaw locking pliers with a rubber sheet jar opener, other was strait jaws. Strafed the brass pretty good, but it don't wanna unscrewith. I thought I heard Murphy inside it, laughing... Anyway, it wasn't marred to the point it doesn't easily slide back into the receiver tube, so hopefully not totaled (yet).
I'm trying to unscrew that valve normal right hand thread, anybody know if that's right? Maybe I should just spray into it with soap and water, then alcohol, and not open it. I'll have to ask Murphy, then do the opposite ;)
I found a diagram similar to the parts, not exact, or maybe I've just got some parts missing. Serial# is 476300952.
I'll post some pics from my phone after this post from the laptop (I needed the keyboard so I didn't spend three days typing this).
O-ring 140-058 at the valve and some kind of end cap ... that one wasn't there.
Oh, yeah, the pellets in the parts bin, they were jammed in the barrel. It held a pump or two for an hour.
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Pics
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Well, OK, was envisioning the valve backwards, I see how it works now. Also, I'm thinking it's all there, and the check valve, well, I suppose there's a good chance it's OK. The brass threads are pooched a little, but I can chase them with a tap and wire brush the mating screw.
All that leaves, hopefully, is o-rings?
There was pretty good suction, pulling out the pump cup/arm, and that assembly looks difficult to rework, so may leave that too. Felt is there, matted, but quite frankly I'm doubting the innards have ever been replaced before.
So that leaves o-rings. One on the outside of the check valve, one in the little cup that the hammer hits to uncover the transfer port, one on the outside of said cup that seals the transfer port sleeve (whatever one might call it). Also some short hose section looking slide-over for that transfer port. I didn't see a gasket for where the transfer port rests on the sleeve - maybe I lost it without knowing, and I suppose silicone grease there might just be all that's warranted (?).
This thread had some great advice on disassembling the check valve. I still may have to do that.
https://www.gatewaytoairguns.org/GTA/index.php?topic=187559.0
For the o-rings and transfer port "hose", is there a kit matching the variant of this rifle? I don't see any valves pictured suggesting the parts I saw on ebay will work for this rifle ... so asking. Maybe a Danco equivalent exists for the o-rings?
Also notable, the forearm is wood, buttstock plastic, barrel is smooth bore, and there is a chamfer for a crown. I'm thinking this might just do good with bb's? If it does, I may be trying to find a home for this rifle with a kid needing his first air gun...
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Hey Steve,
I feel ya on this one. I did find a link to a pretty good video on assembling this rifle. It should help. The guy really likes painters tape.
https://www.youtube.com/watch?v=Ww29Z65BTWo
Cheers,
J~
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Your 760 is from April 1976, by serial number and is the last of the auto cocking variants. The valve O-ring is common and the quad seal can still be had from a number of sources, and was likely the reason it was not working to start.
I agree with you, BBs are the ammo of choice for your rifle, and surprisingly accurate.
I am confident you’ll be plinking away in no time.
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I have a bunch of those #8 quad rings if you need one.
I ordered a pack of them a couple years ago for a self cocking 760 I was working on and ended up with 2 packs of them.
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I have a bunch of those #8 quad rings if you need one.
I ordered a pack of them a couple years ago for a self cocking 760 I was working on and ended up with 2 packs of them.
Can I send you postage? I have need for a few...
Cheers,
J~
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I have a bunch of those #8 quad rings if you need one.
I ordered a pack of them a couple years ago for a self cocking 760 I was working on and ended up with 2 packs of them.
I don't know yet what it's going to take to fix the 2nd one, so in the end I could be looking for 2 + who knows what else. The 2nd one is a 1979 serial numbered gun.
This one held a couple pumps, so maybe doesn't need the pump cup or Teflon (?) "stopper" in the check valve.
I wrote Crosman customer service with a parts list to see what they have because kits can be pricy if they include the transfer port seal...
I appreciate the offer and might just take you up on it - thank you David!
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I have a bunch of those #8 quad rings if you need one.
I ordered a pack of them a couple years ago for a self cocking 760 I was working on and ended up with 2 packs of them.
Can I send you postage? I have need for a few...
Cheers,
J~
I misplaced one pack but still have 14 left and can definitely send a few to you, I should have no problem just putting them inside a letter to mail 'em on 1 stamp.
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I have a bunch of those #8 quad rings if you need one.
I ordered a pack of them a couple years ago for a self cocking 760 I was working on and ended up with 2 packs of them.
I don't know yet what it's going to take to fix the 2nd one, so in the end I could be looking for 2 + who knows what else. The 2nd one is a 1979 serial numbered gun.
This one held a couple pumps, so maybe doesn't need the pump cup or Teflon (?) "stopper" in the check valve.
I wrote Crosman customer service with a parts list to see what they have because kits can be pricy if they include the transfer port seal...
I appreciate the offer and might just take you up on it - thank you David!
From 1980-2012 I believe the only compatible parts would be the stocks roll pins and stock bolt, and Crosman stopped offering parts for the old guns a long time ago so you'll be SOL there unfortunately.
If you do need a couple just send me a PM.
I actually don't even need them so I'll be happy to send a few to anybody who does.
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All the cheap kits with o-rings are sans transfer port, the rest that include it are $20 - $30 price range with stuff like pump cup and felt or new check valve (for incarnations later than 1976).
From looking at the front of the pump cup I can tell it's been replaced, and it was in good shape. So all I'll need is the o-rings and transfer port if I get the valve apart and it's serviceable.
Transfer port has a metal (brass) insert and what appears to be malleable plastic tubing over it. Dimensions suggested by miking the brass insert are;
.1651" ID
.2593" OD
.151" Height + extra "crush" length of about 1/32"
Still haven't asked Elon to see if any of his crew noticed a UFO looking like my roll pin...
WIP, hopefully will hear back from Crosman today though, and am wondering if the same tubing used for this 760 is on other models too (in case I order the o-rings from Crosman)...
I'm thinking Lowe's or an R-C store for some tubing?
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Opinions?
https://www.homedepot.com/p/UDP-1-4-in-O-D-x-0-170-in-I-D-x-25-ft-Natural-Polyethylene-Tubing-T16007001/304185139
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Used refrigerator icemaker tubing.
I didn't see a spring for the bb feeder thingy on top and I lost the roll pin :-[
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That's awesome, Steve. Glad to see it back in service!
Do you need me to mic a roll pin to see what size you need? Ace hardware probably stocks them.
Cheers,
J~
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That's awesome, Steve. Glad to see it back in service!
Do you need me to mic a roll pin to see what size you need? Ace hardware probably stocks them.
Cheers,
J~
Thanks Jeff :D
5/32 punch made a good pivot before I stuck the cotter pin in there.
It's a smooth bore, I may try other bb types, but maybe I need to try pellets in it too.
No Ace Hardware around here anymore, but I might have a kit lying around somewhere from HFS a couple decades ago...
The second 760 serial number suggests 1979 --- probably won't have the same difficulty getting the check valve apart.
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Yesterday, CPH, 10 pumps, 380, 399, 390.
15 pumps, 424 fps
As I said above, changed (only) 4 o-rings. Some cleaning, including the sacrilegious barrel scrub. There was "suction" when the pump plunger withdrew, and no attempt to headspace. I should have deburred the holes for the pin but didn't. The end of the retaining ring for the front seal made it obvious the pump plunger cup had been replaced at some point, which I figured since it looked ok, was an attempt to fix it without success. I left it as-is. Felt was OK, matted, not "fuzzed".
It held 2 pumps overnight.
My $.02 is worn pump tube and seal "taken a set" (not springy, not pushing well against the tube...). I suspect a new urethane seal would up the fps.
Five shots taken, not particularly careful to do my utmost - just to see if it did better with pellets. BTW, the pump arm holds tight against the receiver for a few moments but drops, I'm thinking a new pump cup would fix that, yes?
Oh, yeah, 20 fps spead, I didn't tissue test (probe fit?). I did put some plumbers silicone grease on the bottom and outside surface of the transfer port, as well as the o-ring between valve halves. Sadly, forgot to rub some pelgunoil on the plastic checkvalve piece.
Dented a tin can, didn't penetrate it.
(Oops, filename correction, April 1976)
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That's awesome, Steve. Glad to see it back in service!
Do you need me to mic a roll pin to see what size you need? Ace hardware probably stocks them.
Cheers,
J~
Thanks again Jeff - turns out I had a "kit" of one each various sizes and found a perfect fit. I can mike that one and grab it at leisure. AAMOF, 0.193" X 1". The extra friction of the pin is now holding the pump arm firmly. Interesting!
It's still missing the spring for the top thumb switch that loads BB's into the top "magazine", and the decorative caps that have a little pin running through the roll pin. It gets peened on the ends and you have to destroy it to remove it. JGAirguns sells it I believe but I may not bother.
I've stretched the range to almost 15 yards with those wad cutters, it's pretty accurate.
Someone may have asked if I heard a hiss while pumping ... I'm too deaf for that, but I don't think so as FPS and pumping difficulty increase as expected with number of pumps.
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Stretched to 25 yards - still hits where it's aimed. Found a link to the original manual too --- maybe it's shooting par, as they used lighter pellets than I did and the numbers weren't a lot higher.
Neighbor is having a birthday party for their son, guestimate 4 or 5 years old and I caught the dad outside. Asked if his son could have it and got a yes, so it's got a new home ;D
I'm gonna get a tin of pellets to gift later this week that it shot accurately with, feels good not to rape it for a forestock (for the 1377), a 1976 Crosman 760 deserves better than that.
Next one that came with it is a 1979 model 760, also better condition than I thought it would be, maybe I get that one working too, the forestock on it isn't compatible with the 1377...