Jeffrey Corton’s Diana Seal Tool

As you can probably tell, I’m in the midst of Holiday craft selling insanity and haven’t had time to play with the Rochesters or any other airguns lately.

A while ago I received the following pictures from Jeffrey Corton showing his extremely simple (as in, "why didn't I think of that?"), no machining required version of the seal tool I made for the Diana pistol piston seals. Also scroll down to the bottom for a nice solution to the Crosman model 38 valve tool as well…

All pictures and text by Jeffrey Corton, thanks a bunch Jeff!

1. Parts: seal, electrical end cap (large end diameter slightly larger than piston crown), O-ring, 2" socket extension and socket (slightly wider than the electrical end cap).

2. Work seal over small end of cap.

3. Set end cap inside O-Ring. Press seal using extension/socket down to O-Ring. O-ring is simply present to prevent seal from sliding off the end cap.

4. Final position of seal and end cap.

5. Place end cap over piston crown.

6. Using extension and socket, press seal over end cap and onto piston. Picture has seal already installed and one set to go.

7. Seal pressed in place.

8. Remove extension/socket and end cap should be free.

9. Tada, mission complete.

As promised, a bonus for the Crosman Model 38 valve:

"Don't have a cool lathe like you, so I had to figure out another way to unscrew the Crosman 38T Valve. So: snap ring pliers. See attached pic. I just used the 90-degree attachment, didn't even attach the ends to the plier handles. Just set them in place and twisto-presto. Easy peasy lemon squeezy."

Thanks again Jeff!

Resealing a Diana Model 10, Part 6

Just the stepped washer to do.

With the washer held against the rear piston seal I checked the gap with feeler gages. I showed .021" of gap. Going by my work on the Diana model 6, I want that gap to be .3mm, or .012". So I need to remove .009" off the face of the stepped washer. On the Diana model 6 I made a whole new stepped washer, which meant I could use the old Diana 6 washer for this purpose...

I chucked up the old washer and tried to face off .009...yikes! Totally hardened. Even with carbide I was having a very hard time removing material and getting a smooth face.

So I went out to my surface grinder and ground the face down.

A lovely smooth finish.
I replaced the stepped washer, checked the gap (it was right on) and screwed the end cap back on.

I ran a bunch of pellets through the chronograph, the last 10 shots with RWS 7.0 gr. Meisterkugeln gave me between 491 and 503 fps. That's about what it should be doing.

How accurate is it? Much more accurate than I am...time to practice.

Resealing a Diana Model 10, Part 4

I made a special tool to put the seals on the pistons.

The tool is two pieces. A plastic rod 1/2" in diameter, with a taper on the end and the other end turned to be a slip fit in a piece of brass tubing. The brass tubing is polished on the end for about 5/8" of an inch. It's about 8" long because that's what I had in my box of brass tubing. I could have used solid plastic rod and just bored a hole to mate with the pointed piece.

The assembled tool.

The tool was lightly lubed with thin oil, and I pushed the seal on, backwards from the direction it would be installed on the piston.

The seal was pushed past the plastic tapered piece, onto the brass tube.

I removed the plastic piece and pushed the seal against the edge of the tube.

I held the brass tube against the end of the piston button, making sure it lined up.

I pushed the piston seal off the tube and onto the piston, where it settled with a lovely and almost inaudible click. This was by far the easiest piston seal installation I have ever done, and I will likely use a tool like this every time I need to fit a seal to a piston. I did the same for the other piston recoil seal/bumper.

Almost done...

Resealing a Diana Model 10, Part 3

On I go...

The pistol action is held in the compressor.

I removed the end cap screw, then the end cap and the sleeve. The sleeve is for contact with the hand.

I used a depth micrometer to determine the gap between the rear seal and the end of the tube, .008". I also measured the distance from the end cap shim and the end of the cap, .422".

The pinion cap screws. I removed them.

I loaded the spring slightly with the compressor. As on the Diana model 6 I used my handy tool, a file tang.

With copper sheet to protect the cap I removed the right hand (looking from the top of the action) cap and pinion gear.

The cap and gear.

The rear piston rack in position.

Twisted up to clear the left hand pinion.

I slackened the compressor and the rear piston came out with the spring.

I pushed the front piston most of the way out with a .125 dameter brass rod through the transfer port. Then I was able to pull it out.

I think the front seal is bad.

The end cap shim and synthetic washer.

The synthetic washer was not in the best shape either.

Resealing a Diana Model 10, Part 2

And on it goes...

The trigger.

I pushed the pin out, removed it and put the pin back in so I wouldn't lose track of the orientation of the spring.

The cocking link pin was knurled just as on the 6M.

I punched it out.

The pivot lock screw was removed, then the pivot screw.

There's a washer in there as well.

Heavy washer on the left side.

Thin washer on the right.

I removed this trigger component as well...

And the heavy spring.

At this point the sear clears the piston, so I played it safe and left the rest of the trigger group intact.

This piston cocking shoe would not slide out the front. So I just left it disengaged from the piston. I'm not sure if it's supposed to be able to come out this way, or if the entire trigger group needs to be removed and this inserted from the other end. But it doesn't matter.

Everything ready for piston removal...

Resealing a Diana Model 10, Part 1

As I said earlier, an exceedingly kind reader sold me a Diana Model 10 pistol.

As received, in the box, with manual, test target, pellet tin and screwdrivers. The only problem is that the seals are bad. So I ordered a set from Jim Maccari.

Just a beautiful pistol. The Diana 6M I resurrected shares some of the features, but lacks the styling, as well as the quality.

Grips removed.

The underside.

The barrel weight removed.

Using a ball end allen wrench to remove the spring setscrew.

Removing the shroud retaining screw.

The front sight.

The sight screws were removed, and I drifted it out.

The elevation screw on the rear sight was removed, which exposed the two mounting screws.

Removing the trigger guard screw.

The triggerguard lifts out, but there's a spring...

The spring stayed in place on the guard.

The housing around the trigger is pushed up and off.

The housing.

Still more to do...