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Thread: Fitting new Gem spring -ouch.

  1. #1
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    Fitting new Gem spring -ouch.

    Picked up one of the nicest Gems I have seen. Looks don't always say much about the internals, and this one had no piston seal attached and a broken spring. Turned up a nice fitting polyurethane piston seal and bought spring from Protek. Had absolutely no chance of fitting the full size spring using all my strength and ended up taking off 3 coils to compress it enough to get the thread to start. Is there some method without special tools to get these springs in ?

    Baz



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  2. #2
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    Sealed up

    Don't think many had seals .
    Think they spent ages on the fit ?
    Did you drill and app a thread to take the new seal ?
    Mate said 'yes' to your affirmation that they are a total pain to get back together !

  3. #3
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    Quote Originally Posted by Jimny4x4 View Post
    Don't think many had seals .
    Think they spent ages on the fit ?
    Did you drill and app a thread to take the new seal ?
    Mate said 'yes' to your affirmation that they are a total pain to get back together !
    There was a mashed up leather washer in the end of the cylinder and the piston had a hole drilled in it for a screw so it looked like it originally had a seal. I drilled the hole deeper as it was shallow, the steel was very hard, in fact the whole rifle is good quality not like some other Gems I have seen. Think I have lost a little swept volume with the large seal I made but it shoots well and produces very small groups even with a smooth bore. Also fitted a new breach seal.

    Baz
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  4. #4
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    Question

    I can't open Flickr, Is anyone else struggling or is it just my computer?

    I couldn't view Baz's new Gem so I tried getting in to my own link in faves to the page but it says exactly the same-

    'This site can’t be reached

    i.imgur.com’s server DNS address could not be found.'


    EDIT- All OK now, Had to disconnect from my server and reconnect as everything I clicked on had the same effect!!



    John
    for my gunz guitarz and bonzai, see here
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  5. #5
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    Thumbs up

    Baz, I have one that's very similar to yours, The spring is a flatwound one and may be original to the gun (It's such a mess!!)

    It's the bottom one of these two



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

  6. #6
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    A lot of Gems never had seals they relied on a good fitted piston and the use of oil, I have come across many that have a leather washer in the bottom of the cylinder to minimise metallic contact when fired, the fact that the piston was hardened probably meant that no seal was ever fitted.
    Instead of fitting a seal to the front I've found that grinding a groove behind the head and fitting an "O" ring
    Improves the usability somewhat.

  7. #7
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    Quote Originally Posted by johnbaz View Post
    Baz, I have one that's very similar to yours, The spring is a flatwound one and may be original to the gun (It's such a mess!!)

    It's the bottom one of these two



    John
    Sounds like the broken spring I removed from mine. Protek do standard round section replacements £24 for two posted, but these are not easy to install without making up some kind of jig, (unless you are built like Arnie !).

    Baz
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  8. #8
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    Quote Originally Posted by DAVALI View Post
    A lot of Gems never had seals they relied on a good fitted piston and the use of oil, I have come across many that have a leather washer in the bottom of the cylinder to minimise metallic contact when fired, the fact that the piston was hardened probably meant that no seal was ever fitted.
    Instead of fitting a seal to the front I've found that grinding a groove behind the head and fitting an "O" ring
    Improves the usability somewhat.
    Thanks for that, it makes sense. I wonder why there is a hole drilled in the piston head, unless it was used to centralise in manufacture. Mine was only doing 330 fps when I bought it so I think the leather buffer I removed was blocking the transfer port. Much smoother to cock and shoot now, and I am amazed at the tight groups for the smoothbore. Going to have fun with some darts (plastic covered type).

    Baz
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  9. #9
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    Buffer

    Am guessing that if you used heavy pellets the pressure build-up would be greater so the piston would be slower and the recoil or impact of metal on metal less ?
    Using a Hobby at less than 8gr would rattle your teeth but a Bis Magnum

  10. #10
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    Quote Originally Posted by Jimny4x4 View Post
    Am guessing that if you used heavy pellets the pressure build-up would be greater so the piston would be slower and the recoil or impact of metal on metal less ?
    Using a Hobby at less than 8gr would rattle your teeth but a Bis Magnum
    Heaviest .177 pellets I have are JSB Exact Monster 13.43 grn, think they will fly in quite an arc from the Gem.

    Baz
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  11. #11
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    Seal

    How you managed to get that nice new seal into the action without scuffing it to bits on those threads . . . piece of plastic sheet or coke can wrapped around to protect ?

  12. #12
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    Quote Originally Posted by Jimny4x4 View Post
    How you managed to get that nice new seal into the action without scuffing it to bits on those threads . . . piece of plastic sheet or coke can wrapped around to protect ?
    No need, the compression chamber is a smaller diameter than the thread, similar to the Bonehill Brittania. A problem when you are trying to find an accurate diameter for the seal.

    Baz
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  13. #13
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    Quote Originally Posted by Benelli B76 View Post
    There was a mashed up leather washer in the end of the cylinder and the piston had a hole drilled in it for a screw so it looked like it originally had a seal. I drilled the hole deeper as it was shallow, the steel was very hard, in fact the whole rifle is good quality not like some other Gems I have seen. Think I have lost a little swept volume with the large seal I made but it shoots well and produces very small groups even with a smooth bore. Also fitted a new breach seal.

    Baz
    I bought one of the small ones (cannot remember which model) a few years back and that had a broken flat wire mainspring. It didn't have a piston washer, but just a leather disc at the end of the cylinder. The piston had a hole in the end, which looked like it was for the lathe tailstock. I decided to drill and tap it and fit a leather washer and do away with the disc in the cylinder. I cannot remember whether I made a shallow cup washer or just cut a disc of something thicker. I decided to try the mainspring out of a Webley pistol in it and it worked! Low power but easy to cock. I found the thing shot quite large groups with my preferred classic pellet, the Milbro Caledonian. However, the groups tightened up a lot using Bulldog or Smk Spitfire (the same pellets). I put this down to them having a thichker flange behind the dome.
    Cooler than Mace Windu with a FRO, walking into Members Only and saying "Bitches, be cool"

  14. #14
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    Quote Originally Posted by Benelli B76 View Post
    Picked up one of the nicest Gems I have seen. Looks don't always say much about the internals, and this one had no piston seal attached and a broken spring. Turned up a nice fitting polyurethane piston seal and bought spring from Protek. Had absolutely no chance of fitting the full size spring using all my strength and ended up taking off 3 coils to compress it enough to get the thread to start. Is there some method without special tools to get these springs in ?

    Baz



    I own a nice little GEM in .177

    Mine does not have the washer or a hole on the piston for one.

    They have a leather buffer at the end of the cylinder that acts a cushion for the piston. Mine also had remnants of leather in the cylinder so I just got a 1inch leather washer and cut it in half with a Stanley knife so it would fit correctly. Before doing this the piston would not be held back by the trigger sear...I found this out the hard way and almost broke a finger!

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