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Valve stem not long enough ?

Discussion in 'Anything Airgun Related' started by Hoodster, Mar 29, 2014.

  1. Hoodster

    Hoodster Engaging Member

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    I'm trying to fit a 2 piece anti bounce hammer to my s410 I fit the regulator a few days ago but I didn't bother trying to do anything with it until I got the new hammer.
    Now on the fitting instructions that came with it they say the valve stem should protrude 3.4mm approximately and the inner carrier of the hammer should be around 0.4 to 0.6mm from the valve housing, now my valve stem only protrudes by 2mm and so the inner carrier touches the valve housing.
    So at this point I would be grateful for some help with solving this problem :)

    Thx Rick.
     
  2. Akita177

    Akita177 The Absolute State of Britian podcast

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    you need to remove some metal from the end of inner brass carrier till you have the required gap between the carrier and the valve body/housing.
    I dont have access to any tools so i slowly removed the metal using wet and dry i used 360crit on a flat surface and did my best to keep the brass carrier as flat and straight os possible.
    Removing a very tiny bit at a time till i got i power upto 780fps with JSB exacts, i found having the valve spring tightened all the way in and venturi screw wide open and then getting the correct gap for your guns power the best way to gain efficiency with mine.
     
    Last edited: Mar 29, 2014
  3. Hoodster

    Hoodster Engaging Member

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    Thanks this was my thinking to start with but thought I best get the opinion of more experienced shooters first.
     
  4. Akita177

    Akita177 The Absolute State of Britian podcast

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    I email Rob Lane and he said you would have to fettle the carrier gap for your gun the 3.4mm steam and 0.45 to0.6mm is just there recommend starting place.
    My valve stem protruded 3mm so i guess you might have to remove a bit more brass then i did.
     
  5. terry1001

    terry1001 Major Poster

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    I've just spent half an hour finding and then reading through cloverleafs thread on valve head extrusion and I had remembered correctly he measured the valve protusion on some rifles and found them to measure about 2.0mm. This had been playing on my mind a bit when I saw the drawings of Rob Lanes 2 part hammer as I was sure that 3.4mm was more than had been found. I will measure mine next week and see how it compares but I'm sure it's going to be nearer 2mm than 3.4mm.
    I had put a new valve in my regulated S410 and found that it was reluctant to seal, presumably this is because it only has half the maximum air pressure acting on it to create some deformation and create a proper seal.
    One way to increase the protusion would be to face off the valve head but I would think that 1.5mm would be too much on such a small component and then it would need to be 'bedded in' to the seat.
    I will be making some modifications to my hammer next week, one of which is to slightly increase the distance between the inner part and the valve block by slightly shortening the front part. I'm also considering adding some mass to the inner part and adding some spring preload by increasing the length of the rear part plus some possible changes to the outer part of the hammer as well. At the moment I think my hammer is quite light although I haven't bothered weighing it until I get it spot on but I will check it next time the gun is apart. I would be interested to hear the weight s and dimensions of the Rob Lane hammer for comparison.
     
  6. Hoodster

    Hoodster Engaging Member

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    I was tempted to buy a new valve stem thinking that because my 410 is an early model maybe the stems are shorter than on the newer models but then realised it could equally be that the valve housing the thing that's different so felt that removing material from the inner carrier was the best way.
     
  7. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    To the best of my knowledge the relevant dims of the valve housing and valve have never changed over the rifle's production run. If you have one of the earlier white exhaust valves; don't swap it for a crappy later (black) one whatever you do!
     
  8. Hoodster

    Hoodster Engaging Member

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    I've done a bit of basic weighing and measuring.

    inner carrier 20g inner diameter of 8.2mm length 46mm (I've taken a little off the length)

    outer case 23.9g inner diameter of 10.6mm length 25.9mm
     
  9. Akita177

    Akita177 The Absolute State of Britian podcast

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    Just a pure guess but maybe with a reg fitted the hammer doesnt need to be as heavy due to the constant lower pressure agaisnt the valve, and lets face it the S4xx hammer is bit of a heavy beast to start with.
    It took me multiple goes at the removing very tiny amounts of the inner brass carrier to slowy bring the power upto 780fps as i didnt wont to over shoot and end up using more air.
    During this i tried using hammer wieghts and preload washers this didnt have any effect on the FPS just made the gun harder to cock, though in the future i may try again to see if makes anitbounce hammer work anymore efficient.

    I lost count how many times i stripped and rebuilded the gun as my valve had started leaking so i had buy a brandnew own, Julian Bond on AAOC is very helpful and a good price for spares.
     
  10. Hoodster

    Hoodster Engaging Member

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    I'm trying to achieve a ballance between the hammer & valve spring tensions and how much the hammer can push the valve to achieve the right power output I was surprised to find the original hammer lighter than the 2 piece.
    I'm now wondering what transfer port sizes people have on their regged s400's I felt mine was large enough at 3.7mm.
    And yeah setting up a regulator isn't for someone with no time I done in 2 tanks of air so far and I'm now waiting for a refill tomorrow.
     
  11. terry1001

    terry1001 Major Poster

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    This is why I put some aluminium fillers into the air tube, reduced the volume by about half. I used less air and fewer pellets in shooting strings and it didn't take anywhere near as long. I don't mind using air shooting but I hate dumping it just so I can get to the valve.
    From what I have seen and read 3.8mm is as large as you'd want to go and may be a bit too big. at the moment I've stuck with 3.2mm and 100 bar regulator pressure. You may be able to reduce your regulator pressure, the suggestion I saw from Rob Lane was that with a 3.8 port you could be looking at 80-90 bar.
     
  12. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    Good work - interesting numbers. Is the stroke the same as the old striker? Are you using the same striker spring?


    Yes; a valve held closed by a regged pressure of 80bar has around half the load acting on it that there would be at the midpoint in a well-setup unregged gun's ideal operating pressure range (around 150-160bar) so it's correspondingly easier to open :)

    While it could be lighter I wouldn't say the S400's striker is particularly portly - IIRC it weighs 45-46g; by comparison the striker in an HW100 is about 56g from memory. By contrast the strikers in "previous generation" rifles (AA 100 series and pre-Classic DS Huntsmen) are usually in the order of 100g+!

    Admittedly the strikers in earlier FX guns and the AA S200 are pretty light compared to the 400; though.


    Good work on the ally bars - similarly I use a TDR cylinder (200mm OAL) for testing for similar reasons. This gives a total "test range" of around 50 shots with a .22 Carbine barrel - would be good if I could reduce this a little further though ideally.

    The transfer port size, reg pressure and striker impact energy / momentum are all connected and affect the rifle's output and behaviour when coming off reg. A larger port is good to a point (arguments about irreversible mods notwithstanding ;)) however I suspect going too large will push the "ideal" operating pressure too low; meaning that you'll get a muzzle energy spike when coming off reg.

    I get the impression that striker characteristics can perhaps be altered to manipulate rifle behaviour - I suspect that striker impact energy is directly related to valve lift, while impact momentum is connected to valve dwell.

    Dwell is especially important to un-regged guns with choked transfer ports as the flow capacity of the port is maxed out at relatively low valve lift figures - so once open past a fairly low lift value the valve will not flow any more as the flow rate through the system is restricted by the transfer port. IMO in an unregged rifle valve lift is largely incidental and dwell is the controlling factor.

    Conversely in a regged gun the port is wide open and you're looking to pass a larger volume of lower pressure air through the system. The valve can open significantly further before the transfer port becomes the restricting factor; so lift becomes more important.


    Finally some thoughts on the 2pc Rob Lane striker - notice how the mass of the assembly as a whole (around 44g) is similar to that of the original striker (around 45-46g).

    All else being equal (stroke and striker spring characteristics) this striker should give a similar lock time (proper, striker release to valve stem impact) to the original striker running in an un-regged gun; however since one half of the striker (and around one half by mass) impacts the valve body its energy and momentum are lost - leaving only the "active" part to act on the valve.

    It's conveinient that the striker now effectively has around half the mass, energy and momentum of the original, yet since the valve only has around half the force acting on it the system still works sufficiently. In practice I wouldn't expect this relationship to be completely linear, but shouldn't be far off :)

    Of course this split in mass of the two parts of the AB striker is required since it's the ability of the "inactive" part of the striker to lose momentum and energy as it impacts the valve body on successive striker impacts that reduces their severity and limits air loss.

    If you want to play devil's advocate, knowing that the (regged) valve will now satisfactorily function with around half the striker momentum and energy, moving away from 2-pc anti-bounce strikers would allow you to reduce the stroke of the original setup (probably by around a third) or cut the mass of the striker in two - both of which would yield significant reductions in lock and shot development time. Of course you'd still have the very significant issue of bounce to deal with..

    As usual, there's no such thing as a free lunch :p
     
    Last edited: Mar 30, 2014
  13. XTX

    XTX Donator

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    The people who complain about the cost of fitting regs should read this. Sadly the setup that works well in one S4*0 will not work the same in the next one. They can be a royal PITA.
     
  14. Hoodster

    Hoodster Engaging Member

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    The two piece hammer compresses the striker spring by an extra 3mm and I didn't plan on changing the striker spring but I wouldn't rule it out.
    Just to note that my original hammer is only 40g have you got your hammer weights mixed up or is it my original hammer that's different?
     
  15. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    So you've got a bit more preload so are putting in a bit more striker energy then.

    I'm reasonably certain about the striker weight (which includes bearings / bushes) however I can't be 100% certain that this figure is correct. I'll try and remember to weigh one the next time I get the opportunity :)
     
  16. terry1001

    terry1001 Major Poster

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    I entirely agree, it takes a lot of time to get everything right, even for someone who knows exactly what they're doing which is not the category that most owners fit into!
    This does touch on the quality control issue as two seemingly identical rifles will almost certainly require different settings.
     
  17. Akita177

    Akita177 The Absolute State of Britian podcast

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    My findings where pre-load and hammer wieghts had no influence of the FPS with the anti bounce hammer i assume with how it works brass carrier gap with the valve body was the main factor on that side of the gun.
    The only hammer wieght i used was the oring that came pre-fitted on the anti bounce hammer.
    The TP port i had just the point on the end of the grub of the screw no thread showing in the TP i felt i lost compression other wise, but as XTX says S4xx are a pain in the rear end.
     
    Last edited: Mar 30, 2014
  18. Akita177

    Akita177 The Absolute State of Britian podcast

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    Has anyone considerd fileing the point on the venturi grub screw flat?
    Being flat you could have it flush with the wall of the transfer port so its fully open but not lose any compression?
     
  19. Hoodster

    Hoodster Engaging Member

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    I did look at the grub screw but figured with it fully retracted the small cavity left because of the shape wouldn't cause much disruption to the air flow.
     
  20. Akita177

    Akita177 The Absolute State of Britian podcast

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    With a cavity there could be some loss of compression, possible small loss in power/efficiency.
     

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