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PostPosted: Sun Mar 20, 2016 11:39 am 
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Joined: Fri Mar 18, 2016 6:43 pm
Posts: 12
Hello, I have a Crosman 766 that was my dad's I replaced the valve with the closest valve I could find to buy, Here's the change:

Image

And it works!! :D :D :D

The only problem is that its not nearly as strong as I'm pretty sure it should be, and its unable to pierce an pop can (at 10 pumps)
i've changed this valve and the all seals I could find, and am not sure as to why the power just isnt there. please help!


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PostPosted: Sun Mar 20, 2016 4:07 pm 
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Joined: Tue Oct 13, 2009 1:27 am
Posts: 2514
Location: Vancouver
I'm not familiar with that model, but at a guess it seems likely the shorter replacement valve isn't allowing nearly so much compression as the original, longer valve. This is a pumper, as multi-stroke pneumatic I take it? Ah yes, watching a Youtube clip shows basically how it works. So yeah, my guess stands, it seems most likely that you're getting a lot less compression with the shorter replacement part. I'd consider cleaning up the original and making it work, along with any interior polishing or other measures to make sure it's sealing properly everywhere.


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PostPosted: Sun Mar 20, 2016 7:03 pm 
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Joined: Tue Mar 17, 2015 7:43 pm
Posts: 168
Location: Estrie, Québec
I think that if you kept the original piston with your shorter valve, there is some chance that the piston does not make its way up to the valve and push just a little bit of air in it at each pump.

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PostPosted: Sun Mar 20, 2016 7:36 pm 
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Joined: Thu Jan 08, 2009 4:20 pm
Posts: 262
Location: Markham , Ontario
Would it not be possible to rebuild the old valve ?


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PostPosted: Sun Mar 20, 2016 7:39 pm 
PGAir wrote:
I think that if you kept the original piston with your shorter valve, there is some chance that the piston does not make its way up to the valve and push just a little bit of air in it at each pump.


That's what I'm thinking. I know when I did my flatop pistol/valve on another airgun I needed to adjust the piston length. Sounds like its too short and compressing air.


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PostPosted: Sun Mar 20, 2016 8:11 pm 
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Joined: Tue Jun 03, 2008 5:46 pm
Posts: 2815
Location: Canada
Will agree....an adjustable piston is needed. Something like this...I don't have any more, but would suggest you contact DerekVinyard on the forum...

Image

Al


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PostPosted: Sun Mar 20, 2016 9:26 pm 
Gippeto wrote:
Will agree....an adjustable piston is needed. Something like this...I don't have any more, but would suggest you contact DerekVinyard on the forum...

Image

Al


But with the cup end like factory. Flat top pistol won't do well on that valve.


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PostPosted: Sun Mar 20, 2016 10:43 pm 
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Joined: Fri Mar 18, 2016 6:43 pm
Posts: 12
An update: I went back to the old valve with the insides of the new one, however, on the old one theres that bit that jets out which is which leaks, but if I'm fast enough pumping and shooting it fires and oh my is it ever strong, ive never fired a bb gun before and have only used airsoft, and holy sassy molasses is it cool.

On EricTheRed's post from some time ago, he had the same exact problem, and he filled where the detune thing connected with jb weld, and it seemed to work for him, im just wondering if thats my best solution, or if some other stuff would work better


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PostPosted: Mon Mar 21, 2016 8:51 am 
Encii wrote:
An update: I went back to the old valve with the insides of the new one, however, on the old one theres that bit that jets out which is which leaks, but if I'm fast enough pumping and shooting it fires and oh my is it ever strong, ive never fired a bb gun before and have only used airsoft, and holy sassy molasses is it cool.

On EricTheRed's post from some time ago, he had the same exact problem, and he filled where the detune thing connected with jb weld, and it seemed to work for him, im just wondering if thats my best solution, or if some other stuff would work better


I would get the old valve repaired. I don't think your going to get the other valve to work without a longer piston. If it works better with the proper valve and it leaks well. Thats better than a valve that wont even punch thru a tin can because it cannot build up enough air.


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PostPosted: Mon Mar 21, 2016 10:57 am 
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Joined: Thu Sep 01, 2005 1:41 pm
Posts: 997
Location: GTA
Unscrew the blow off valve and look for a seal. I just checked a valve in my parts bin, it looks like it has a home-made seal. I think it's supposed to be an oring, or an oring should work.
You could also try a bit of Teflon thread tape on the thread to see if that seals it up. Just don't put any on the first few threads, you don't want bits of tape coming off and getting in the valve.

That blow off valve is how they detuned the gun to keep it under 500fps for Canada. If you plug it you will need your PAL, or risk breaking the law.


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PostPosted: Sat Mar 26, 2016 7:33 pm 
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Joined: Fri Mar 18, 2016 6:43 pm
Posts: 12
So if i wanted to seal the hole, what would be the best stuff to use? Thanks for all the info


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PostPosted: Sat Mar 26, 2016 8:27 pm 
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Joined: Tue Oct 13, 2009 1:27 am
Posts: 2514
Location: Vancouver
Tap threads into the hole and Loc-tite in a set screw. Just did that on a valve for Barfman (has his PAL) on a multi-pump rifle he picked up on a great sale. Worked a charm, bringing velocity right up to the velocity he was after.


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PostPosted: Sun Mar 27, 2016 12:05 pm 
Encii wrote:
So if i wanted to seal the hole, what would be the best stuff to use? Thanks for all the info


It's not the blow off. Its your valve is too short.

Rebuild your old valve. Than try. Your not getting enough air.


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PostPosted: Sun Mar 27, 2016 6:24 pm 
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Posts: 12
RobertMcC wrote:
Encii wrote:
So if i wanted to seal the hole, what would be the best stuff to use? Thanks for all the info


It's not the blow off. Its your valve is too short.

Rebuild your old valve. Than try. Your not getting enough air.


Thats where I'm at right now. The old valve has been "rebuilt" (new seals and exhaust stem) all thats left is the blow off which leaks air


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PostPosted: Sun Mar 27, 2016 9:20 pm 
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Joined: Sat Apr 23, 2011 10:13 pm
Posts: 201
If i remember right, i measured the hole, looked at my tap drill chart and find the closest tap for that hole size. Tapped it and used loctite on the proper sized bolt. Cut it off and filed it round like the body of the valve. That was many years ago on a 760, but looks the same. HTH.

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