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Air Gun Home Forum Index » Rifles » Crosman 760 early varient
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Crosman 760 early varient 
PostPosted: Wed May 04, 2011 6:52 am Reply with quote
boatwiser
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Hello AirGunHome,

I was lucky enough to find the same Crosman I had as a kid back in the late 60's - a pre Coleman Crosman 760 in real nice shape at a local flea market. It pumps and shoots but only if you pump it real fast. When pumping it slow I can hear the air leaking out of the barrel everytime I open the pump handle to add another pump of air. If I don't open the pump handle for another pump the gun holds the air.

I took the whole gun apart and everything looks super clean including all O rings. The only thing I have not taken apart is the brass valve assembly because I don't want to damage the brass casing or if there is a plastic part inside by applying heat to it. Should I just put some oil on all the parts and put it back together?

Any suggestions would be greatly appreciated
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PostPosted: Wed May 04, 2011 10:07 am Reply with quote
AirGunEric
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You need to take the valve apart to determine what is causing your leak. Do not apply heat to anything- it's brass- you grab the two halves hard enough and twist and it will come apart.

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PostPosted: Wed May 04, 2011 5:41 pm Reply with quote
boatwiser
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I tried as hard as I can to unscrew the brass valve body and it won't budge. I thought I read the valve body had Locktite on the threads and heat was needed to unscrew it?? Any other suggestions - I really did not want to grab it with pliers and risk damaging the brass valve body. Thanks for any info.
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PostPosted: Wed May 04, 2011 8:39 pm Reply with quote
AirGunEric
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There's no loctite- just age.

Put it in a vise with rubber jaw pads and use a slip-wrench with rubber over the teeth (or visegrips with same).

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PostPosted: Thu May 05, 2011 9:43 pm Reply with quote
boatwiser
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Alright now - got it apart by putting the valve body in a vise with a soft piece of pine board on each side to protect the brass from the vise jaws. Then took a piece of old rubber tire tube and wrapped it around the other end of the valve body and gripped it with a set of channel lock pliers and it came right apart.

Everything looks good - cleaned up and put back together and still had a slow air noise coming out of the barrel after each pump - it was better than before but not fixed for sure.

The only thing I can guess is the valve cap at the rear end of the valve body is letting the air escape while in the closed position before the trigger is pulled - is there a seal inside that cap? What other seal could it be?
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PostPosted: Thu May 05, 2011 10:10 pm Reply with quote
AirGunEric
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There is a stem with a cap- if cap is worn you could have a leak. Also, if the valve spring supporting the stem is weak from age/fatigue it may be assisting with the leak. Replace both and you should be good to go.

Also, just in case it hadn't been pointed out, cock it before pumping.

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PostPosted: Fri May 06, 2011 6:34 am Reply with quote
boatwiser
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This is the 1966-1970 version of the 760. It is self cocking and there is no stem on the valve. Here is the picture from Crosman.

Inside the valve body from front to back is the plastic reverse flow button followed by an aluminum spacer followed by a spring. The back of the valve body has a nipple that a brass cap slips over. I think this brass cap is the air release valve when the trigger is pulled letting the air pass the cap and enter the transfer port to the barrel.

I tried to post a photo but it comes out so tiny you can't see it.

http://mywebpages.comcast.net/boatwiser/crosmanleak.jpg
http://mywebpages.comcast.net/boatwiser/crosmanvalve.jpg

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PostPosted: Fri May 06, 2011 8:34 am Reply with quote
Crosman140
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I'll follow boatwiser's lead.

Here are two files from Crosman you might find helpful.

This is the owners manual for a 1966-1975 from Crosman's website.
http://crosman.com/pdf/manuals/C760SC-OM.pdf

And here is the parts diagram from Crosman as well.
http://crosman.com/pdf/manuals/C760SC-EVP%20&%20PL.pdf

A little story: My first air rifle was a Daisy Powerline 880. This is Daisy's direct competitor for the Crosman 760. When I was a kid, I was torn between the two. I didn't have the money for both, so, looking at the power rating from each company, I selected the Daisy (they boasted more, but probably not true). But I have a soft spot in my heart for both models.

OK, one more story about the 760 in my life: When I was about 10, we lived on a farm. We had a real problem with angry crows that would dive-bomb us when ever we went outside. So, my parents had another kid from our church bring his Crosman 760 over to shoot them.

I was sooooo jealous. Shocked My parents wouldn't buy me a gun. My mom thought I'd shoot my eye out. So, to add insult to injury, they had this kid flaunt his fine piece of airgun craftsmanship right in front of me. Evil or Very Mad Crows were dropping and I had nothing to do with it. I just stood their drooling.

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PostPosted: Fri May 06, 2011 10:09 am Reply with quote
AirGunEric
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Forget that they "look" good- they could be hard and dry after 40 years.

The seals/o-rings are part numbers:

140-058
130-034
130-035

130-034 and -035 aren't likely causing your current issue- 140-058 could be. If the spring (111-026) is weak, then 140-004 and 1400A29 may not seat correctly. In all likelihood it is both the spring and 140-058 at this point.

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Crosman 760 early varient 
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