At least it is unlike any in the three or four gun I've had. The pics are also a bit blurry, but it looks like there has been a black disk added to the top of the piston as a seal support. Most LG55 pistons I have had have a beveled edge that terminates at the flat top of the piston. It looks like a 45 has been turned off the piston edge.
It's quite possible that you can remove this modification and apply a standard seal, assuming that the threaded post on top hasn't been changed.
Many of the threaded seal posts get bent due to being shot with a worn out seal. It's an odd thread that is almost impossible to find, so ost people conver the piston to use an R-7 seal by turning of the threaded post, then drilling the piston for a screw to add the HW seal adapter. JG airguns can make this mod for you, and it's well worth it in a gun that you plan to use as a shooter.
That might help. The old seal you have actually looks melted in the out-of-focus view. That may have been a homemade part, too, that wasn't designed to stand up to the beating it has to take.
Since it may indeed be customized (with that intermediary washer I can see that's been added to the original threads on the piston), maybe you can use an Apex or other JM seal and size the OD. The opening where it snaps on the piston will also need to match whatever is on there now.
The other plan would be to take off the homemade, custom-threaded piece and go back to using the original style seal from JGA. He also sells the threaded nut that holds the OEM piston seal onto the threads, IF they didn't re-size the threads, too.
Adding all of that up, you may have your work cut out for you there.
Ed, The Airgun Tune-Meister
"We can rebuild the squirrel. Make him stronger, faster...We have the technology"---Skyler M.
You can see in the LGV picture that the support plate is integral to the seal, but in the LG55 it is placed under the seal and the seal is then screwed down.
In the LGV seal the tab probably slides into a keyhole milled into the top of the piston. I say probably because I've never been inside an LGV. However, you may want to try soaking the piston in WD 40 overnight and then seeing if you can slide the seal support sideways on the piston to find the keyhole and remove it. Then it's a simple matter of replacing the seal. Your seal suppport may also simply screw off. It may be a design that was a limited run, setup to screw on to the piston head of the LG55. If so, it may be loctited on and you'll need to put some heat on it to get it off.
screw the metal thing off, turn the diameter down so it fits inside an R-7 seal, and screw it back on upside down using it as a Weihrauch seal adapter. You'll probably need some additional spacing washers to get that to work.
The tapered part at the front looks reversed from what I remember when rebuilding my LG55. I had to make a special forked wrench to grip that part with it's two slots in each side, kind of like a wide flat screw driver blade with a slot cut out for the threaded stem.
I think the taper was facing the piston, and widest part was facing the front, like you would expect a dovetail to work. I had a hard time screwing the dovetailed nut off the threaded stem but was able to save it. I got my piston seal from JG Airguns, and it was clear I believe. Screwed it back tight and all was well.
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