Apologies to Sheridan Aficionados - forgive me

[threesuns]

Spent a fair bit of time the last couple days trying to get this SKB reseal sorted out. Making some progress.

1rst up poppet seal … not too difficult resizing a standard size faucet washer to fit.

2nd and a bigger problem was the valve gasket as I didn’t enough of the original to get decent measurement from and wound up making some shims. They are the same size as the OD of the brass valve body and the same ID as the step. Stacked with an O-ring against the valve body as the seal.

Never was able to get the check valve seat out. It appears to be a rubber gasket sandwiched under the smaller valve nut. Not sure if it’ll be any good, as now air bleeds past the pump cup near the end of the closing stroke. Some pressure is building in the valve and it does fire. But I m going back it to see what I can do with the cup seal.

[threesuns]

Well I did expect an over-molded cup!

[threesuns]

Finally used an item from the Sheridan reseal kit, I had on hand.

The Sheridan cup cone is deeper than the lip. Removing the button would leave a hole and figured I might be able stretch it over the retention plate on the SKB pump, if I could reprofile the cone to allow adequate seal compression under the plate as I squeezed it into the compression tube.

After adjusting the pump link. The pump is working beautifully!

Since I have a new cup and poppet seal I decided to tackle the check valve and kind of glad I did. I couple taps with a regular screw and the seal crumbled. Cutting a sliver from the Sheridan cup button to use as the new check valve seal, I m now in a quandary. It doesn’t seal! I have great compression on the first pump stroke but neutral out when the cup passes the vent on the second stroke.

It does hold over nite. So I know my cup and poppet are good. Anyone have and ideas?

[TerryM]

  What do the springs look like?  Might you need a slightly stouter check valve spring?

[threesuns]

I have wondered since getting inside if the 2 inches of compression on the hammer spring fatigued the valve spring over time. It definitely overpowers it and the rifle must be cocked before pumping.

I know I don’t have any cone type springs laying around. I will have to check google.

Or maybe even a different seal material? or thicker cut, would reduce volume sightly, but allow the spring to exert more force on the little brass check valve disc?

[threesuns]

Update … Check valve just does not want to seal. Softer rubber gasket didn’t work nor did adding small spacer to increase preload on valve spring with both gasket materials.

Sensing my frustration, my wife suggested I might need professional help.

And after restless nite I had to admit, she might be right! Grabbed a small bag of goodies and headed out to talk with a local machinist. I lied and told him I not in a hurry BUT … I m confident that this SKB will soon be shooting again.

Stay tuned

[threesuns]

My modified check valve for the SKB is done!

Sacrificed a 13xx valve, as I only want the check valve seat, and removed the nose rite B4 the screw hole and had the remainder threaded to match the SKB part, which happens to be 15 x 1mm. Had it threaded long so I could cut to length as needed. I know I lost a little volume but since this is .177 cal not sure it will make a huge difference. Also figured the O-ring seal would be more positive than the rubber gasket.

[Goose]

Nice work! 

Happy to see you making progress with it.

J~

[threesuns]

My check valve mod worked and I finally was able to shoot the SKB. Standard weight pellets at 6 pumps, leave the muzzle at 650fps. 10.65gr Barracudas, I’ll say 600fps as a memory aid, but are actually average 590. So 8FPE for both.

I couldn’t do more as after 6 pumps it would start leaking out the barrel. And wouldn’t even hold 1 pump after that. Thinking it was my poppet seal, I ventured back inside but nothing looked amiss. Reassembled without any changes and same issue again, seal failure after 6 pumps! Going back inside, once more I see no evidence of what/why this is happening.

My education continues. Only working till noon so will be back at it this afternoon.

[threesuns]

Made a top hat today to replace my shim stack. Since the exhaust 1/2 of the valve is threaded past the TP down to the step for the check valve, got to thinking 1 O-ring to seal on the step and another to seal the body of the valve would more closely duplicate the original thick seal.

Also put the hammer spring on a diet, shortening it 1 inch.

Initial pumping just after valve reassembly seems good. Time to finish assembly and send some lead over the chrony.

[threesuns]

Before I get to some addition performance data - loosing 1 inch off the hammer spring appears only to be positive.
1) reassembly was easier 2) trigger pull has improved. Atleast it seems better to me.

Spent the first few shots sighting in at 6 pumps and did not notice a change in fps. 8 pumps recorded just shy of 700fps with standard weight pellets. Max power, heaviest pellets I have at 10 pumps.

Noticed 1 pellet that this SKB really likes. I’ve got a vintage Galaxy 4x15 scope made in Japan that needs a home. Wonder which intermount will fit?

[threesuns]

Forgot the 3rd + with loosing 1 inch of hammer spring; the rifle no longer needs to be cocked B4 pumping 👍

There is still 1 issue I am intending to address, and Jirushi had a similar issue with his rifle. Some shot pressure escapes via the threaded portion of the tube, for the valve nut, around the valve body and out the alignment hole. Just plugging the hole won’t be enough for significant performance gains, though I intend to do that. Notice the stains on the stock and the smooth area where that pressure has affected the original rough texture of the bedded area.

Added: Well I m proved wrong again! 1rst shot with 16.2 JSBs and 10 pumps resulted in a 30fps gain! Just shy of 12ft lbs now.
            10gr Baracuda’s are over 610fps with only 6 pumps! I m very happy with that.

            Gotta look for those intermounts.

[oldair]

threesuns, many thanks for documenting your SKB saga.  I acquired one of these a year ago, and have put off a re-seal job mainly due to the forward valve body seal shape and buried check seal (may try a stainless ball for that).  My hammer spring is unduly strong, same as yours & Louis's.

Don R.

[threesuns]

YW Don. That is one reason I really like this forum. Knowledge is not shared for profit or gain, just the promotion of this great hobby we enjoy.

There is so little info on the SKB air guns be sure to post your progress and performance results.

Reflecting back on my experience the poppet seal is very similar in design to the my kessler and early crosmans. I bet a the 109, 110, 105, and 106 “check valve seal” (I think the poppet seal would be too small) could be used with little to no mod. JG Airguns still sells them. I thought about a ball for the check valve too, my kessler uses 1, but I didn’t have an appropriate size to try. Lastly because the piston head is threaded on, 1 of Tim’s delrin flat top heads could be made to fit. Thats what I did with my Kessler.

[threesuns]

Crosman intermounts fit perfectly. The Galaxy 4x15 scope, made is Japan, is I believe about the same age as the SKB and is a good fit.

[TerryM]

 Zowie, what a cool gun!  Thanks for sharing!