I'm getting around to the rebuild, and I thought someone might be interested in what I'm doing with this leather sealed gun.

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In the picture above you can see the seal as it came out of the gun. The seal itself is in great shape. It's firm, and still retains some of the original lubes from when it was new. However, note that the retaining screw has a circular mark on it from continuously impacting the transfer port. There should be enough leather proud of the retaining washer to keep this from happening. So, I took it apart to check it out. Here's a pic of the seal off the piston.

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Take a look at the leather backing washer. Note that it has been bent from firing, and consequently the leather has been pushed back to the point where it now sits flush with the retaining washer, causing the impact imprint on the screw. If left unresolved this could lead to thread damage.

You'll also note the picture of the seal. It has a new green backing washer installed and it was screwed tight to give you an idea of how much leather might be proud of the piston. You'll also note that the green backing washer is off center. It seems the guy who built the piston ended up with a pilot hole for the washer retaining screw being drilled slightly off center. Upon further examination, I realized that the leather was almost flush with the piston side allowing for metal to metal contact during the firing cycle.

After pondering how to solve this ( as in fill and redrill/retap the hole) I decided to convert to synthetic. Below you can see the new seal and adapter. The adapter was built in a single piece and the installed on the piston head. It was then chucked in the lathe for final shaping to insure that the adapter would be concentric with the piston head. A seal was then turned on the lathe and fitted to the adapter, and then it was turned down to a tight fit. Final shaping and sizing will occur after about 100 rounds have been put on the seal.

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This solution will allow me to return the gun to a full OEM condition some day, flaws and all, if that's what I choose to do once I'm done.

Well that's it for now. The power keeps going out here, so I'll get back to this later & save the battery on my laptop for some work I need to do.

Regards

Keith Knoblauch

and nice pics of your solution....my 27 was quite a bit rougher inside, and lacking lathes & such I opted for a JG seal and new spring. It's better, but still shows it's age!

thanks for all the detail, and for sharing.

Matthew

You turned the piston seal yourself? What material is that?

Great work.


Nick,
From ruralburbian Philomath.
anotherairgunblog.blogspot.com

http://straightshooters.com/chat/viewtopic.php?t=4835&sid=2ee83a19547aae7359e3b96cf30a24b1

I looked over your blog regarding the Slavia seal. There's a lot of similarity. First adapt the seal material to the piston head, then cluck it up and shape it. Looks like you've got fancier gear than I do though.

I'm going to watch the rolled shoulder on the piston. It could reshape the seal over time causing it to compress back the same way as the leather did & I may need to switch to an adapter with a supporting shoulder, or get some stiffer seal stock somewhere.

Regards,

Knobs

I'm going to get in some harder urethanes to play with, 80 seems rather soft for anything with real power. Of course what I really need is a rubber hardness tester so I can check existing seals and reverse engineer...

Urethane rubber is wonderful stuff. I'm always amazed at the beating it takes in my hydraulic die forming, squishes to a fraction of it's original thickness and flows across the whole face of a die, yet comes right back to near the original form. It does degrade at the 10-20 tons of pressure I subject it to, which must be many orders of magnitude greater than the experienced as a piston seal.

From your straightshooters post:
"So.....the nutty part of all this.....I've probably got close to $2500 into my lathe, 5C chuck and collet set, and measuring gear......so I've got a $2500 adapter and seal here!! LMAO"

Yeah, it's funny how much money I have tied up in my shop, considering the little jobs I do. Then again I do use the shop for a whole bunch of other purposes, so it does ultimately pay for itself. Of course as I also sell machines, I often have to convince people that rather than buying a $2000 CNC mill to make $10.00 replacement parts for their hobby, they might be better off just buying the dang part. But when it comes to unobtainable airgun parts (or other rare items), it is lovely having the capability, isn't it?


Nick,
From ruralburbian Philomath.
anotherairgunblog.blogspot.com

......you'll stumble around for a few tries and then the light will come on. If you pay attention to what you think will happen, and then look for indications of whether you are right or not, you should be able to build your experience level and be able to select appropriate materials and make adjustments to how you make the part. There's more than one way to skin a cat.

It's ought to be obvious that no one seal material fits all uses. The flip side is that just because your seal looks like something that is sold off the shelf doesn't mean it will perform the same way. For example, I'm not sure that the lube groove will be deep enough as it now exists to avoid being bulged into the side of the receiver tube under firing compression. I also don't know if the parachute groove will work as intended. I may be better off putting a shallower groove closer to the edge, or even possible hogging it out like the old power pulse seals were done. All stuff to look at.

Yes it is nice having the equipment. I'd like to get a mill, but I don't really see a need to blow 4-5K on a mill and tooling to set up with a decent DRO and tooling. You can drop 20K on tooling in a heartbeat, and that's for gear that'll keep you within half a thou............but that's all I need.

Knobs

Based on Knobs's excellent material in these posts, over the last few days I undertook assembling a sort of "Frankenplinker" from the remains of two abused Diana model 27's. One is a German-market .177 from the mid-1950's, with faded blueing and a horrifically refinished stock; the other a sight-less, rust-bucket .22 Winchester from the early 70's, with a busted trigger blade.

No machined seals or anything from my clumsy hands, mind you, but the newer one had a particularly fresh-looking piston seal and spring. After re-conditioning the leather, and a bit of metal polishing, they went into the older hull together with a fresh breech seal and the usual dose of JM lubes. The result has exactly the same power as both my pet 80's-vintage RWS 27 and recently JM'ed R7 (650's with Hobbys, 590's with Superdomes) so I'm calling it a win.

Knobs was absolutely right about one thing: after years of reading about the horrors of the feared ball-sear trigger, I have to say that taking apart and re-assembling these little guns was really a total anti-climax.

That being said, I did find a spring compressor to be a necessity--not because of any earth-shaking forces, mind you, but just so you can go slowly and keep everything aligned. But basically it's just a matter of stacking up the bits and shoving 'em straight in, nothing to it. Dudes....if I can do it, ANYBODY CAN DO IT. Really.

Now to get to work on that old finger-groove stock....I can't possibly make it any worse!

You're the Man!! LOL

Yeah, I use a bar clamp to put 'em back together. Makes for easy work.

Knobs