The Gem piston washer

[Phil Russell]

Having been a 'Gem virgin' until a few days ago I will soon post my experiences in getting an old 'Gem' style rifle back into shooting condition. But one aspect surprised me ... the piston washer seemed to be rivetted to the end of the piston. It was about 10mm thick, with the rivet being about 8mm diameter and peened over a steel washer to hold the leather (?) washer in place. This Gem has no maker's name but I had not seen a piston washer like it ... are all Gem's the same and do they strip in the same basic fashion?
Cheers, Phil

[Benelli B76]

Did not think Gems had any washer at all. Just a metal piston.

Baz

[Phil Russell]

Hi Baz ... that is interesting and I am in no position to disagree as I suspect it goes to show that there are several designs within the generic Gem family. This was definitely of a leather type material ... approx 20mm diameter (the cylinder bore) x about 9mm thick with an 8mm hole through which the piston rivet went. The piston itself has no piston rod, the trigger sear acting on a raised flange on the front of the piston body. The cocking lever pushes against a flange at the rear of the piston body. There is a spring guide fastened to the end block in the stock, about 3" long and maybe 10mm diameter. As you can imagine, there is plenty of clearance around the spring inner diameter.
Cheers, Phil
PS sorry about mixing imperial and metric ... comes naturally!

[Benelli B76]

Phil, I made the mistake of thinking one was missing from mine and fitted a polyurethane one which did not help as it took up swept volume. There is a blind hole in the end of the piston and I think some guys fit their own washer. Read further down on Dannys website. Perhaps a few had washers but never seen one..


https://forum.vintageairgunsgallery....isenwerke-gem/

[ggggr]

Having been a 'Gem virgin' until a few days ago I will soon post my experiences in getting an old 'Gem' style rifle back into shooting condition. But one aspect surprised me ... the piston washer seemed to be rivetted to the end of the piston. It was about 10mm thick, with the rivet being about 8mm diameter and peened over a steel washer to hold the leather (?) washer in place. This Gem has no maker's name but I had not seen a piston washer like it ... are all Gem's the same and do they strip in the same basic fashion?
Cheers, Phil

I've only seen a couple of Gems Phil and I dont like them. On one of the little ones (forget model number) there was a piece of leather down the cylinder with a hole for the transfer port. Now I cannot really see that movng one it have been fired a few times, but I drilled and tapped the end of the piston and fitted a leather cup washer.
I guess many years ago someone could have rivetted one. DCL Dave might be able to tell you more as he had a lot of bits for them at one point.

[johnbaz]

Having been a 'Gem virgin' until a few days ago I will soon post my experiences in getting an old 'Gem' style rifle back into shooting condition. But one aspect surprised me ... the piston washer seemed to be rivetted to the end of the piston. It was about 10mm thick, with the rivet being about 8mm diameter and peened over a steel washer to hold the leather (?) washer in place. This Gem has no maker's name but I had not seen a piston washer like it ... are all Gem's the same and do they strip in the same basic fashion?
Cheers, Phil

Hi Phil

I picked this old Gem up cheap with a spare .25 barrel which I can't use as it's not a T bar barrel lock!!



There was no stock filtted but I found one at Melbourne for a fiver!! (Off Mel, I was going to make one from the block of walnut until I found the one off Mel!)
It was really pitted and in a state, The thing was so siezed that the cocking link/Trigger guard snapped when I tried loosening it!, Luckily the other barrel had one that nneeded minor modification



The piston seal was missing but should be held on with a large flat head bolt as in this pic, Had a fair old job removing it as can be seen from the damage at the edge!!



I used a 30"x1" linisher to grind through the pitting down to good metal on the curved parts and a file (Draw filed) on the flat lands of the barrel!, Tried cold blueing them both but as usual, Came out crap!!





Never did get around to finishing it, Anyhow, Here's a nicer one that I also got from Melbourne later than when I picked up the stock




John

[Phil Russell]

Not sure that the mystery deepens or not. I got the butt plate off my Gem and the stock even has the rifle number on it, stamped into the wood under the plate ... in this case the number 48. The stock is clearly held on by a through bolt from the end of the action, similar to BSA rifles of old. I did not remove the stock from the end block that screws into the cylinder.
Looking at all the photos, I am not sure I have seen a rifle like mine. On top of the cylinder is a sprung lever maybe 10cm long that you depress to raise the breech unlocking end. The breech itself has a bar protruding with a rectangular cut out which engages with a matching shallow (c. 1mm) dovetail on the cylinder, the sprung lever acting to disengage it. Maybe I should try to get a photo as I find it difficult to describe. It is not a T bar.
The issue of lost volume occured to me when I came to fix a new piston head so ... purists stop reading ..... I cut a bit off the end of the rivet rod so that when the new head was in place the overall length of the piston plus head was as before.
Maybe my Gem had been modified in the past? There is certainly evidence of someone else having been inside ... vice marks or whatever on the cylinder are a giveaway and the spring is round section whereas I am led to believe that Gem type springs are flat section ... or are they all? There was clearly some sort of 'finish' to the cylinder and trigger block when the rifle was in its prime. Unfortunately this is long gone, or rather what remains of it, which is not much, has become somewhat corroded.
Cheers, Phil

[Phil Russell]

Well well, having worked through the superb photos in the link provided it appears that my rifle is, or very similar to, the Eisenwerke Mod 13 ... the barrel catch is just like that shown.

Thank for all the help.
Cheers, Phil

[Phil Russell]

More opportunity to look at pictures. I wonder if I have a Model 13A? The pictures I saw show the rifle with a black stock. My rifle had remnants of black paint on the stock and I assumed, maybe incorrectly, that someone had painted it. Where the paint had worn away (most of stock) the timber showed a nice walnut (?) oiled (?) finish.
Cheers, Phil

[Benelli B76]

I may be wrong, but looking at the piston design and the lovely finish on the piston surface I would say that the johnbaz piston has also been modified to take a washer. In some cases this can drop the power output.

Baz

[Huttles94]

I had a nice little GEM a while back, has since left my collection but that one did not have a piston seal. I mean it worked fine and the only reason I took it apart was to see what it looked like on the inside (something I do with all antique guns I buy, even if they seem to shoot like new, I always take a look).

Kind of made me worried so I got a random leather washer out of my spares box, carefully sliced it in half (So I had two thin washers) and carefully placed it down the cylinder to act like a cushion. Granted that was probably not going to do it any favours but at the time it seemed like a ok thing to do

[Benelli B76]

That is the most common thing I have found, no piston seal but a very thin leather washer as cushion at the end of the compression chamber with with hole for transfer port as also mentioned in ggggr post above.

Baz

[DAVALI]

hi Phil,
Both of my gems have no piston washer only a thin leather “Buffer” fitted at the end of the cylinder, the one you saw at LV last Saturday being one of them,
Dave.