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Jumping fps on TX200 MK3

Discussion in 'Technical' started by Corbarwolf, Nov 30, 2016.

  1. Corbarwolf

    Corbarwolf Member

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    Need some assistance, struggling to identify the problem with my TX200 mk3. For no obvious reason she will jump 70fps for 20 or more pellets then back again and keep alternating. Tonight I took my target out to 27yrds and zeroed when running at 730 ish. Combro used to check every pellet. Inside she has the original air arms steel guides and top hat bur with the tbt short stroke kit fitted. This combo gave a nice feel and around 10.2 fpe. But this jump puts her around 12.5.
    As you can see the groups are consistent and at the 735 area lovely to shoot. What is going off? View attachment 148745
     
  2. hmangphilly

    hmangphilly Posting Addict

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    No 1 job
    make sure you can trust your chrono
     
  3. simonc_here

    simonc_here Engaging Member

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    I'm not sure the chrono will be making the group move like that.

    Something binding inside causing fake preload that goes away after a few shots?
     
  4. Corbarwolf

    Corbarwolf Member

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    putting the chrono aside for the moment, even assume it's completely useless, something is causing two poi's for alternating quantities say 30 then 20 then 20 etc
    I agree Simon it feels that way, but what could it be I wonder.
    is this symptomatic of dieseling?
     
    Last edited: Dec 1, 2016
  5. Poison Dwarf

    Poison Dwarf Engaging Member

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    You have installed a new kit. Spring guide OK?
     
  6. Corbarwolf

    Corbarwolf Member

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    currently the original steel guide (seems to be fine) and steel top hat is in as the delrin tuned guide felt tighter so tried to eliminate that as a problem but left the short stroke extension on the piston as this did feel better and gave a resultant 10fpe thereabouts.
     
  7. rich79

    rich79 Lovin the smell of cordite in the morning

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    Is it a square section spring in a TX? Might be catching on the end of the spring guide compressing it more between the guide & TH?
     
  8. Nickg

    Nickg Busy Member

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    Make sure the short stroke spacer is concentric to the piston and rear bearing, if not as the piston rotates it will hit a tighter area and slow the piston down , there is more to this tuning lark than meets the eye :rolleyes:
     
  9. Corbarwolf

    Corbarwolf Member

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    Not square section and round wire seems pick up free both ends.
    Couldn't make it any more concentric, but hey worth another look on both counts.
    Does the spring continue to rotate slowly in circles in a single direction or release back to the start of the rotation?
    When the seal is retracted does grease pass under the leading edge and when thrust forward does the seal leading
    skirt flare outwards against the inner bore applying more pressure
    collecting spare grease as it goes?
    all a school day eh:up:
     
    Last edited: Dec 1, 2016
  10. Corbarwolf

    Corbarwolf Member

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    Could breech seal failure cause this effect of 2 alternating POI?
     
  11. greyskull

    greyskull Busy Member

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    I would think if breech seals were iffy it would be lower on power all the time, if you need any, speak to 'Dag' on this forum about replacements.
    Regarding the piston seal "collecting spare grease as it goes", can I ask how much grease you have on the seal / comp tube inner wall, it only needs the lightest of smears, otherwise it could migrate to the front face of seal and maybe give dieseling?
    Are there any witness marks on the short stroke nose conversion?
    Would it be worth putting it back to standard spec as a test to see if your consistency returns.
    Not much help I'm afraid, but worth looking at all avenues I suppose, and the TX is so easy to pull apart and look inside.
    Good luck,
    Atb Nev :thumb:
     
  12. JoeHeugh

    JoeHeugh Beware the Springer

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    My guess is dieselling given the power jump so check for smoke / smell. Short stroking increases chamber pressure which increases temperature. Seems 20 odd shots might be depleting a fuel reserve which then replenishes itself slowly. I'd open her up, degrease and then give a light lubrication. You can examine the internals at the same time for any scoring or damage which might suggest another cause. Check the colour of the piston seal too, white ones will appear brown / yellow stained if there's any combustion going on.
     
  13. Brett80

    Brett80 Engaging Member

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    Try another batch of pellets. Perhaps you have a mix of head sizes?
     
  14. Oat

    Oat Very Active

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    Dieseling?
    Otherwise i would recommend a strip down, clean, degrease and regrease. Remember that more is less where grease is concerned.
    If still no luck i would put it back to standard spec and test it - that way you can rule out if the issue is with one of the modifications.
     
  15. waisted skirt

    waisted skirt Donator

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    There is no way that this would be responsible given the FPS we are talking about.
     
  16. Brett80

    Brett80 Engaging Member

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    Not head size, you're right! But I've mixed a tin of Diablo field and Diablo field express without realising and had this result. Managed it on Tuesday while not paying attention.
     
    Last edited: Dec 1, 2016
  17. Corbarwolf

    Corbarwolf Member

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    Last night I took photos of the internals. Too much grease ? Wiped away and reapplied Moly as shown this blob covered the piston seal and the 2 oil rings. No obvious scoring damage in chamber. Stroke extension as concentric as I left it and not loose. Breech seals looked in good order. (10 photos per post limit - 1st set)
    View attachment 148852 View attachment 148853 View attachment 148854 View attachment 148855 View attachment 148856 View attachment 148857 View attachment 148858 View attachment 148859 View attachment 148860 View attachment 148861
     
  18. Corbarwolf

    Corbarwolf Member

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  19. Corbarwolf

    Corbarwolf Member

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  20. Nickg

    Nickg Busy Member

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    I am talking about the piston rotating, freely
     

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