Quick Fix--The Smith & Wesson 78G from the Findlay Show

Fifteen minutes after getting back from the Findlay, OH airgun show, the S&W 78G sprang a leak. The seller had just gassed it up last Thursday and it was still holding two days later.

I've been looking for a clean 78G on and off for about a year. Mostly off. Friday night before the show, I put this gun at the top of my list. There were probably half a dozen S&W 78/79Gs and Daisy 780/790s there. This one looked well cared for and the price was very reasonable. I assumed when buying it that I'd need to replace all the seals anyway--that's just par for the course when buying a vintage CO2 gun.

Nick has brilliantly covered 78/79G rebuilds before here. Sorry for the redundancy, but maybe a few new pics will help someone--besides, the grip project I'm working on isn't quite ready for prime time.

Unscrew the threaded end plug below the barrel--S&W calls this the "sleeve retaining screw"and remove the "power adjustment extension" rod.

Removed the casting assembly screw.

Had some difficulty getting the extension sleeve out. A #2 pencil--eraser end first--pulled it right out.

The orientation.

The extension sleeve looked slightly peened on the ends. Perhaps this caused the difficulty in removal. With the lathe, I took a few thou off each end.

pulled out the bolt stop pin. It was a very slightly bent. I gently straightened, then polished it.

While the bolt was out, I replaced the bolt o-ring. Forgot to write it down. I think I used a #6 viton.

Removed the valve body screws. One on the left side,

Another pic.

Two on the right.



Brass valve assembly pulls out. This one was a bit stuck. Decaying o-rings sticking to the die castings.



S&W calls this the "cartridge connector". Uh, OK.

When I pulled out the valve body plug, the source of the leak was obvious.

The o-ring had the consistency of a gummy bear.

Took a bit of time to scrape it all out of the groove.

Another pic. Used a #12 viton o-ring as a replacement.

Might as well replace these, too. Used #6 viton o-rings on the "cartridge connector".

The valve stem seal looked fine. A bit of Crosman pellgun oil on all the o-rings and it was back in business. Refer to Nick's original posting series for reassembly. There are no surprises or tricks. It's a very straightforward design.

Soon: match grips for a Daisy 7X7.