Gem Pattern

[stevegv8]

Hi Steve,


Looks like another LZ/FLZ...

I does look like a machined fit piston (and damper washer, as you say in the end of the cylinder) so if it has a screw hole it will have been done by a previous owner sometime in its past...but are you sure it is actually a screw hole? ...as these some times had hole in the end of the piston as a by product of manufacture...

I had already decided on closer inspection the hole in the piston isn't very deep and has no thread so doesn't look like it has a conventional cup type washer involved.
I was assuming the possibility of tight tolerance washer less piston and an absorbing material at the end but didn't think the method really likely.
Looks like this is what it is though, I'm wondering if I could modify using a 23mm Diana type washer and tap a thread in the piston but why improve a crude design anyway? So I'll stick with the factory spec now I know what it should be.
The transfer hole in not central and the damper is, so the alignment isn't quite right, so I'll make a new one with a bigger hole in case it rotates. Now I have all the crud out of the latching groove it should solve that problem too.

Thanks Dave

[DCL_dave]

I had already decided on closer inspection the hole in the piston isn't very deep and has no thread so doesn't look like it has a conventional cup type washer involved.
I was assuming the possibility of tight tolerance washer less piston and an absorbing material at the end but didn't think the method really likely.
Looks like this is what it is though, I'm wondering if I could modify using a 23mm Diana type washer and tap a thread in the piston but why improve a crude design anyway? So I'll stick with the factory spec now I know what it should be.
The transfer hole in not central and the damper is, so the alignment isn't quite right, so I'll make a new one with a bigger hole in case it rotates. Now I have all the crud out of the latching groove it should solve that problem too.

Thanks Dave

No probs

Glad you are keeping it original, they do work surprisingly well as a friction/machined fit with just a scant wipe of grease to keep them sealed....but, be warned that if you were tempted to drill and tap it that these types of pistons are usually made from very hard steel and are known (to me atleast) to break bits and taps...

[stevegv8]

No probs

Glad you are keeping it original, they do work surprisingly well as a friction/machined fit with just a scant wipe of grease to keep them sealed....but, be warned that if you were tempted to drill and tap it that these types of pistons are usually made from very hard steel and are known (to me atleast) to break bits and taps...

I did notice though that the rear end of the piston is the sealing end as it is a fraction bigger than the front end so the front end must float to a small degree.

[DCL_dave]

I did notice though that the rear end of the piston is the sealing end as it is a fraction bigger than the front end so the front end must float to a small degree.

The rear end of the piston travels in the wider section back end of the cylinder, and is pinched up with the rear cylinder/end plug bolt. The front of the piston travels in the honed out but slightly smaller front end of the cylinder and this effects a good seal (unless it is worn beyond sealing) look inside the cylinder you should notice a slight ridge just before the sear mounting point and an ever so slightly smaller cylinder diameter at the front.

[DCL_dave]

Do you notice how the very simply design allows the piston to freely float/rotate as the torque from the spring unwinds...thus ensuring no torque steer to twist the shot off aim also allowing for even wear to contact parts, a trait the modern tuners aim for I believe...these bad boys were a hundred years ahead of their time!

[stevegv8]

Do you notice how the very simply design allows the piston to freely float/rotate as the torque from the spring unwinds...thus ensuring no torque steer to twist the shot off aim also allowing for even wear to contact parts, a trait the modern tuners aim for I believe...these bad boys were a hundred years ahead of their time!

Excellent info on the Gem, I thought the thread wasn't going to offer anything up now my questions are all answered!

[harry mac]

Itseems to me that these rifles are of relatively low value. Has anyone on here done a full renovation. Stock refinished, cylinder replated and barrel and trigger guard/cocking lever reblued?
I'd love to see just what one looked like when you unwrapped it from the grease paper, having brought it home from the shop of Mr Lincoln Jefries.