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Thread: S400 Tuning Info

  1. #1
    Protea Benchrest (Air) Team '17/'19

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    Default S400 Tuning Info

    Hi Guys

    I recently bought a S400 Classic with an extra long air cylinder.

    The rifle shoots very consistent with a spread of approx 15 ft/s.

    My problem is that it chrony's at avg 740 ft/s. This = 10.3 ft/lbs with JSB pellets. I have tried the grub screw adjustment on the right of the rifle, but it makes little or no difference to the power.

    Can someone please supply me with some tuning info/doc's, or point me to a web site where I can find the info required to up the power closer to the 12ft/lbs mark.

    I know there are guys that can tune it for me, but I would like to have a go at it first, if I can get the required info.

    Thanxs
    Kevin
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  2. #2
    Protea FT Team '08

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    Long story short.If it has the longer cylinder it should be tuned already.

    If it is running under power I would say the main hammer spring is getting a bit old.

    If you dont know what you are doing dont fiddle.

    Strech the main spring and I bet you will be back on target.Problem is if that fixes it it wont last forever.
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  3. #3
    Protea Benchrest (Air) Team '17/'19

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    Am I correct in the following assumption.

    If I increase the tension on the main hammer spring it will release with a bit more force and keep the exhaust valve open for a split second more. Thus more ft/s.
    I was thinking of doing this with a washer/shim at the rear of the spring or a nylon washer at the front between the spring and the hammer.

    Increasing the hammer weight or reducing the tension on the exhaust valve spring should also increase the valve timing.

    thanx
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  4. #4
    Protea FT Team '08

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    Quote Originally Posted by dutoitk View Post
    Am I correct in the following assumption.

    If I increase the tension on the main hammer spring it will release with a bit more force and keep the exhaust valve open for a split second more. Thus more ft/s.What I would do
    I was thinking of doing this with a washer/shim at the rear of the spring or Good plan a nylon washer at the front between the spring and the hammer.Dont do that

    Increasing the hammer weight or reducing the tension on the exhaust valve spring should also increase the valve timing.None of these

    thanx
    Thats the way I see it i am not an expert but mine runs like a dream
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  5. #5
    Sharp Shooter
    Doctor BAM

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    Kevin

    I am prepared to help...... A washer / shim at the rear of the spring will do the trick.....
    I will make it out of delrin (nylon) and it will probably be a 5mm spacer....
    I also have a chrony to check the velocity for you....


    malan
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  6. #6
    Inactive Member

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    Malan, the max of that shim on a Air Arms can only be 3.5mm. If longer it would not cock due to the travel of the cocking shaft be shorten.
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  7. #7
    Inactive Member

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    The way I do it is to fit a spacer of 3.5mm in front of the main spring, to do it at the rear the sping guide is a problem.
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  8. #8
    Sharp Shooter
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    You are right, Wally

    I have also learnt the hard way if the spacer is more than about 4mm thick...
    I would also have to assess the existing hammer spring if I am allowed to work on the rifle under discussion.....


    malan
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  9. #9
    Protea Benchrest (Air) Team '17/'19

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    Hi Guys

    Thanx for the input but I have found the cause of my problem.

    It goes by the name of "DON'T SCRATCH IF IT DOES NOT ITCH, AND MORE SO IF YOU DON'T KNOW WHAT THE F$#@ YOU ARE DOING"

    I bought this rifle second hand and I can't point fingers at the previous owner as it has changed hands before he had it. (but I do have my suspicions)
    Some one in its previous life decided to modify the rifle to beyond FAC with a few MINOR changes.
    The transfer port in the Firing valve body as well as the bolt housing was drilled and hollowed out to approx 5mm.
    The hole in the firing valve body is so big that the adjuster grub screw just turns into empty space.
    The Brass fitting on the barrel had its port soldered close and a new port drilled and reamed on the opposite side.
    The firing valve was damaged by the drilling of the transfer port and finally the hole in the brass pot has been reamed.

    All of the above was enough for me to throw my toys out of the play pen and I just stopped short of smashing the rifle against the wall.

    Thanx to Louis and Rudi who will hopefully be supplying me with the required parts, and with some advice from a few fellow airgunners, I should be able to restore the rifle to original.

    So Guys, if you get the itch, make damn sure you know where to scratch. I can't keep replacing broken toys in my play pen.




    Last edited by dutoitk; 28-10-08 at 18:34.
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  10. #10
    Sharp Shooter

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    Sorry to hear mate,

    I would like to know who did such a nasty job to the rifle and then sells it in that condition!!!!!!
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  11. #11
    Inactive Member

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    Aijaiiiii!!!!! Thats no good, are you getting the parts for free? Install your new parts and tune.
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  12. #12
    Protea Benchrest (Air) Team '17/'19

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    Wally

    I am Married,...... Nothing is free.

    I just transferred the funds to Louis and he is sending the spares via Speed Services.
    Hope to have it up and running by Saterday.

    Ian

    I bought it threw the CapeAds for a good price (R4500). I grabbed it because it has a long air cylinder. I have never had a bad deal before but there is always a first time. Should have stripped it down before taking it.
    Another life lesson.
    With new spare's it is still a good price and a wealth of S400 knowledge was gained.

    Kevin
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  13. #13
    Sharp Shooter
    Doctor BAM

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    Kevin

    The offer still stands..... Let me know if you want help to chrony it......
    The AA S400/410 does not have a fancy tranfer port as such, and the fact that you were getting good consistencies with tampered parts shows it is a good design.....

    malan
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  14. #14
    Inactive Member

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    True, very true Malan.
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  15. #15
    Protea FT Team '08

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    Glad you found out now.

    I am sure the new parts well restore your guns performance.
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