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Theoben Evo He

Discussion in 'Technical' started by Ian Mawdesley, Jan 21, 2020.

  1. Ian Mawdesley

    Ian Mawdesley Well-Known Member

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    Hi all , will a HW90 gas ram fill adaptor, fit a Theoben evo only getting 8.8 fps out of the evo would just like it to be up a bit thanks
     
  2. drolraw

    drolraw Active Member

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    Pretty sure it won"t. If it was pre HE I would say yes.
     
    Ian Mawdesley likes this.
  3. Blackmax

    Blackmax Forum Rude Guy

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    Probably just needs recharging with a pump. Recommended fill pressure for HE is around 40 bar +/- depending on calibre.
     
  4. robs5230

    robs5230 Oversprung

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    Best fittings sell a fill adator that has both the HW90 and Theoben threads ( you remove one part to reveal the other thread).

    However, I'd be looking to find the reason why power has dropped.

    If the piston seal has started to deteriorate, adding more air will only further worsen this.

    It could be a failed schrader valve. It could be any of the internal seals.
     
  5. Ian Mawdesley

    Ian Mawdesley Well-Known Member

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    Thanks for the replys the gun has been in an atic for 10 years so ot been used took it to local rfd and they have pumped up the gas ram and currently doing 11.3 so some improvment going to chrono it again in a few days just to see
    Regards Ian
     
  6. Blackmax

    Blackmax Forum Rude Guy

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    They all leak at some point. By checking the fill pressure to see if it’s correct at least he won’t have to strip it all and it may well just be a loss of pressure.

    If the power is low with the correct pressure then he does need to look elsewhere.
     
    TORNADOS7, Ian Mawdesley and robs5230 like this.
  7. The Squire

    The Squire Engaging Member

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    Hopefully that will sort it then if it’s been left for a good while. Beware though if the muzzle energy drops off again quickly, could be a deteriorating piston crown (seal) which are quite expensive compared to the same component on a springer.
     
  8. Blackmax

    Blackmax Forum Rude Guy

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    Not easy to source either, I think Impact have the only stock.

    I wonder if the Zephyr crown really worked anyway?
     
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  9. TORNADOS7

    TORNADOS7 Top Poster

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    If you decide to get the adapter and use a stirrup pump to do the job then be very "very" careful as it don't take much to overfill them, when I did mine I just primed the pump, lent on it until the air inside compressed and then gave it a little squirt, about a quarter of a stroke (in fact probably less) was more than enough, in fact if I remember rite I had to let a little out as it was too high and it took me a couple of attempts to get it right...
     
    Blackmax likes this.
  10. Blackmax

    Blackmax Forum Rude Guy

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    This is how I’ve done them, because you have a gauge for reference.
     
  11. hmangphilly

    hmangphilly Posting Addict

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    zephyr.jpg theoben slr.jpg

    No idea what that's supposed to achieve
     
  12. Blackmax

    Blackmax Forum Rude Guy

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    The upper photo is the Zephyr and along with machined channeling in the cylinder it's supposed to direct air to the transfer port making the gun more efficient. Not sure it was ever scientifically proven and it's had its doubters.

    The mounting design looks pretty close to some BSA seals I got off Cloverleaf so I wonder if you could use them.
     
  13. robs5230

    robs5230 Oversprung

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    For what it's worth, I think the Theo seals are terrible.
    Totally too hard in my opinion.

    I've removed those Zephyr seals and its clear to see they have been spinning around on the piston. Plenty of evident marks to show that from TP imprints / combustion.
    They'd only be efficient if they didn't rotate.

    The should have fitted a seal like the parachute seal HW uses, or even the old Venom Powr Pulse seal.
     
    The Squire and Blackmax like this.
  14. hmangphilly

    hmangphilly Posting Addict

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    It looks like cobblers to me

    but I’m in a funny mood
     
  15. Blackmax

    Blackmax Forum Rude Guy

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    Me too! :laff:
     
    hmangphilly likes this.
  16. The Squire

    The Squire Engaging Member

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    So it sounds like the forum has decreed that the Zephyr philosophy is waffle and flim flam! Think I'm OK with that.
    The seals certainly aren't the best, and I'm sure that a few years back there was a particularly bad batch of Evolution style seals. I'd bought a .177 Evo by post (bad move) and the seller hadn't realised the seal was u/s :rolleyes:
    To cut a long story short I got a new one that lasted about 6 weeks, I thought I'd done something stupid so bought another and it lasted about the same. Fortunately I ended up speaking to someone with a common understanding at the supplier who sent me some replacements FOC, they were a lot more compliant that the first couple which had failed by the front face cracking through about 120degrees circumferentially.
     
  17. Ian Mawdesley

    Ian Mawdesley Well-Known Member

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    This is all getting very technical, I will chrono on sunday and see if the evo is up to the job.Thanks for all the help
     

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