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Thread: Gem Piston Washer Replacement

  1. #1
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    Gem Piston Washer Replacement

    Can anyone give me some guidance on how to replace the piston washer/s on a Gem piston.
    Currently looks like two leather washers separated by a thin metal washer with another washer on the end all held in place by I assume a screw with the head ground down.
    Many thanks in advance
    Steve

  2. #2
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    Never seen one with a piston washer fitted. They have a thin leather washer at the end of the cylinder to act as a buffer. The steel piston is a good fit to the cylinder to produce pressure. Years ago, like you I thought it needed a piston washer and I made a nice fitting polyurethane one and the power went down.

    Baz
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  3. #3
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    Gem piston washer

    I worked on a Diana gem type recently. The piston seal was made from string and grease which was disintegrating and it was not powerful enough to launch a pellet. I replaced it with a 3/4 inch tap washer with a 15mm hole punched in the middle as I had one to hand. It fits well and shoots nicely at 3 ft/lb.

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  5. #5
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    Quote Originally Posted by Stefran61 View Post
    I think that is not a piston washer assembly per se,but a sandwiched leather disc intended to be oiled and act as a reservoir of lubricant for the cylinder.

    The steel disc acting as the piston crown appears to be riveted on and not the remnants of a squashed screw head.

  6. #6
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    I think that one of the key indicators is that most Gems have no facility on the end of the piston to fit a washer, no hole with screw thread. My Gem had a centering dimple from the manufacturing process. I tapped it myself to fit a washer which was not needed.


    Baz
    Last edited by Benelli B76; 20-09-2020 at 02:18 PM.
    BE AN INDEPENDENT THINKER, DON'T FOLLOW THE CROWD

  7. #7
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    That's interesting as I have another stripped down and it too has a leather washer/buffer bonded to the end of the piston so seems common that these are fettled to try to improve output.
    In both cases the leather is very well compressed, I have had them soaking in Neatsfoot for a week and there doesn't seem to be any softening of the leather.

    Steve

  8. #8
    micky2 is offline The collector formerly known as micky
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    I have had a Gem with a leather washer glued to the end of the piston. but what as been said above they are just a very tight fit metal to metal.

  9. #9
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    It seems to be mostly Diana and Langenhan types of Gem pattern that may have a piston washer of some type fitted, have seen the usual cup washer types as fitted to the later Diana 6 as well as the more unusual stacked leather disc type and the greased hemp string type as well in some LZ/FLZ Gems too.

    EG and Marck Gems are usually a machined fit metal to metal and they work surprising well if not too tired and worn...

    If you have a lathe its quite easy to cobble something up, but if not and the seal is knackered then you have to improvise as best you can...if you want authentic then cut off the old crap off the piston, punch out some oversized leather discs, punch centre out and put a few slits in the leather radiating out from centre hole, soak it in warm water for 10 minutes or so and see of you can stretch it over the piston head, if successful repeat...once you have all the stacked discs on the piston dip it in boiling water for 30 seconds to a minute to shrink the leather back on the piston head leave it to dry and shape to final size...
    blah blah

  10. #10
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    Quote Originally Posted by DCL_dave View Post
    It seems to be mostly Diana and Langenhan types of Gem pattern that may have a piston washer of some type fitted, have seen the usual cup washer types as fitted to the later Diana 6 as well as the more unusual stacked leather disc type and the greased hemp string type as well in some LZ/FLZ Gems too.

    EG and Marck Gems are usually a machined fit metal to metal and they work surprising well if not too tired and worn...

    If you have a lathe its quite easy to cobble something up, but if not and the seal is knackered then you have to improvise as best you can...if you want authentic then cut off the old crap off the piston, punch out some oversized leather discs, punch centre out and put a few slits in the leather radiating out from centre hole, soak it in warm water for 10 minutes or so and see of you can stretch it over the piston head, if successful repeat...once you have all the stacked discs on the piston dip it in boiling water for 30 seconds to a minute to shrink the leather back on the piston head leave it to dry and shape to final size...
    Good advice from an expert!
    I have a couple of FLZ gems with the stacked discs and what I have done is carefully ground the end of the riveted stub and removed the steel and leather washer stack. I then fitted the cup washer from a primus stove pump with a leather tap washer to reinforce the centre. then fitted a steel washer and re riveted the piston. All works ok

  11. #11
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    Quote Originally Posted by WebleyWombler View Post
    Good advice from an expert!
    I have a couple of FLZ gems with the stacked discs and what I have done is carefully ground the end of the riveted stub and removed the steel and leather washer stack. I then fitted the cup washer from a primus stove pump with a leather tap washer to reinforce the centre. then fitted a steel washer and re riveted the piston. All works ok
    Sounds like a good plan if the steel on the piston stub is workable/ can be peened over again. Sometimes the steel used in some gem pistons is extremely hard and difficult to drill/machine (possibly case hardened?) if memory serves, that is usually the machine fit piston types though.
    blah blah

  12. #12
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    Quote Originally Posted by DCL_dave View Post
    Sounds like a good plan if the steel on the piston stub is workable/ can be peened over again. Sometimes the steel used in some gem pistons is extremely hard and difficult to drill/machine (possibly case hardened?) if memory serves, that is usually the machine fit piston types though.
    Yes they are very, very hard.

    Baz
    BE AN INDEPENDENT THINKER, DON'T FOLLOW THE CROWD

  13. #13
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    Many thanks for all the responses.
    Steve

  14. #14
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    Thumbs up

    Hi

    I have a Gem that had a big screw holding a rotten leather cup washer when I eventually got it apart!

    I've cleaned them up here, Had a hell of a job removing the screw as it was siezed in place!


    The gun was a heck of a mess, Paid a tenner with the .25" spare barrel, Was going to make a stock but found one on Mel's table at Melbourne for a fiver!!




    I snapped the trigger guard/cocking link whilst tring to get the piston to move, Luckily it came with a spare on the other barrel (Can't use that one as it's not a T bar Gem!)..



    Plenty of emery cloth, Draw filing on the flats of the barrel and I got it shiny!!




    I then messed it up trying to cold blue it!!




    I should finish it really, Can't even remember where it is now


    John
    for my gunz guitarz and bonzai, see here
    www.flickr.com/photos/8163995@N07/

  15. #15
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    You can see how the piston head is ground and polished for a perfect fit in the cylinder. Not usual for a piston with seal fitted .

    Baz
    BE AN INDEPENDENT THINKER, DON'T FOLLOW THE CROWD

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