Saturday, February 7, 2009

Resealing the Smith and Wesson Model 79G, Part 1

Now to fabricate the valve stem seal. When I did the Crosman 167 I tried to punch the seal from sheet but didn't have good results. This time I decided to try a different type of punch and fabricated my own.

Drilling some tool steel before reaming a 1/8" hole.

Drilling the other end 19/65"

Reaming to 5/16"

Turning a 10 degree taper on the end. A file was used to clean up the end and put a secondary bevel on the cutting end. I did not harden the punch, but may in the future.

A 1/8" dowel pin provides a removeable pilot.

Some 1/8" thick 95 durometer urethane was punched with an 1/8" hole.

I inserted the dowel pin in the hole.

And slipped the punch over it.

Using the arbor press I was able to make a nice concentric seal.

Inserted in the exhaust valve.

The stem was slipped in and then pressed all the way home. I have no idea why I forgot to take a picture of it pressed all the way in, I guess I got excited. The replacement seal stands a little proud of the brass body, I'm assuming it will compress a bit from use.

The large valve o-ring was replaced with a viton one.

The two small o-rings were replaced with viton ones.

The valve reassembles in reverse from disassembly.


Anonymous said...

Wow I have been wondering what goes in the valve body. Was trying O-rings and they just don't work. I have a model 78G Ser # 0055798. and have it 99.9% rebuilt except for that darn valve body. Can relate to your trigger spring woes.... been there !! LOL !
Got mine brand new in 1974 and havn't shot it in 25 + years. After buying a Beeman P 17 pistol recently, I got motivated to fix the old pistol. I have changed the six o-rings but that flat washer seal was a mystery to me. All my O-rings were all like Cheerio's. And that washer was nothing but a gray mass of mush. When I got my pistol back then I also got a case of 50(10 boxes of 5) S&W 12.5g co2 powerlets. Still have 5 boxes left.!! I assume that you have to fabricate the washer??? What Durometer hardness rubber did you use ?? Will be waiting to see something on the blog. This is a great blog !!

Felice Luftschein said...

As I said in the post, 95 durometer urethane rubber sheet, 1/8" thick that I punched out. You can get a new seal kit I believe from Bryan and Associates or other airgunsmiths if you don't want to repair the valve stem yourself.

Bill Marsh said...

This is excellent,very helpful and accurate.
My only suggestion is to mention that the barrel set screw should be loosened before separation of barrel and frame and then carefully tightened after final assembly. This will help make a good seal between valve and barrel.