Resealing Older Airguns

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Diamondback

Diamondback

Member
Nov 29, 2017
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Tx, United States
Anyone have the oring sizes for Crosman 150/157, 112, 160, 180?


How about the S&W 78G & 79G?


Had this info in a computer that died.


I realize some seals, like the Crosman seal around the piercing pin at the valve / powerlet union in a 2240 / 2250 / 2260 is a factory part, as well as the seal on the valve stem.


FWIW I found seal info for the Crosman MKI & MKII:
"I’m not promoting the use of substandard seals but these standard o-ring sizes are what I found to fit and function in the Mark pistols, at least temporarily.
- Bolt seal (Mk1) = ¼”OD x 1/8”ID x 1/16” thick
- Valve body seal = 5/8”OD x ½”ID x 1/16” thick
- Piercing pin seal = ¼”OD x 1/8”ID x 1/16” thick
A quick email to Tim at Mac-1 resulted in the correct o-ring sizes for the Mark pistol seals. Tim recommends mil spec 90 durometer urethane seals for all applications, although a softer seal will work on the bolt.
- Bolt seal (Mk1) = 006 softer seal (005 with hard seal)
- Bolt seal (Mk2) = 004 softer seal (003 with hard seal)
- Valve body seal = 014
- Piercing pin seal = 005
- Piercing body seal = 113"
 
S&W 78-79 O-ring sizes

part 11041 #006 3 needed

part 11047 #012 1 needed

part 12226 #113 1 needed

all should be urethane and all can be found at The O-ring Store, should be duro 90

of course you need to make something for the valve and I have been using leather punches and 1/8 urethane sheet goods

any co2 gun, if the gas touches the O-rings try to use urethane always
 
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Resealing & Orings for Smith & Wesson 78G & 78G Pistols, & Daisy 780, 790 & Model 41

Here is some general info with oring sizes for resealing these air pistols. I included the sources where I found the info at the bottom of the page.

The piercing cap has two O-rings, a large outer Oring and a smaller inner oring that sits inside the piercing cap
assembly, around the piercing pin.
The large outer Oring is a -113 = 9/16″ ID, 3/4″ OD, 3/32″ C/S.
The smaller oring inside is a -006 = 1/8″ ID, 1/4″ OD, 1/16″ C/S. Please note you will have to make a special tool
which fits inside the piercing cap to get to the smaller seal. It's basically a flat screwdriver of the correct size with a notch taken out of the blade tip to protect the piercing pin.

The main valve has three O rings.
The larger seal around the valve assembly is a -12 = 3/8″ ID, 1/2″ OD, 1/16″ C/S.
The two smaller seals on each end of the small pipe that connects the valve to the frame are -006 = 1/8″ ID, 1/4″
OD, 1/16″ C/S.
The Oring on the larger 22 caliber bolt probe of the 78G is a -005 = 3/32″ ID, 7/32″ OD, 1/16″ C/S.
The Oring on the smaller 177 caliber bolt probe of the 79G wasn't listed, but another online post said a soft oring
sized 004 should work in a Crosman MKII 177, and that a 003 should be used if using hard seals. I'm guessing these
sizes would be a good place to start with the 177 caliber 79G bolt probe.

The main seal inside the valve, on the valve stem, is not an oring, and removing and replacing this seal is
probably beyond the capabilities of most home gunsmiths because you need a press and some fittings to press the
valve stem out of the seal housing without damaging the valve stem or seal housing.

In case you’re interested, I found another online post where the poster used 1/8" thick 95 durometer urethane sheet to
make this seal. They took a piece of this urethane sheet and punched a 1/8" hole in it. Then made a punch / cutter
that they sized to 5/16" and punched out a seal. The finished seal had squared edges with an inner hole of 1/8", an
outer diameter of 5/16", and was 1/8" thick.

Finally, the transfer port from the CO2 chamber to the barrel is a factory part with a metal-to-metal seal. Some
people have used an oring or orings for the transfer port and supposedly got better performance, but I didn't find
the size. Also, I don’t know if an oring or orings were put on the ends of the factory transfer port part, or if
the factory part was replaced with an oring or orings. Maybe ice maker tubing would work, like on QB and Crosman
22XX airguns?

Sources:

https://pistolplace.wordpress.com/2014/09/21/vintage-air-pistol-review-smith-wesson-78g-and-79g/ 

http://anotherairgunblog.blogspot.com/2009/02/resealing-smith-and-wesson-model-79g.html
 
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S&W 78-79 O-ring sizes

part 11041 #006 3 needed

part 11047 #012 1 needed

part 12226 #113 1 needed

all should be urethane and all can be found at The O-ring Store, should be duro 90

of course you need to make something for the valve and I have been using leather punches and 1/8 urethane sheet goods

any co2 gun, if the gas touches the O-rings try to use urethane always
Click to expand...

Thanks for your contribution Marflow, much appreciated.

I found some info on them too, so I included it as well.

Many Thanks to MMCM13, biohazardman, and far_shot for your help too.

Kind Regards, db
 
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