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Thread: Update on the Diana piston (would like some input )

  1. #16
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    To me , this looks like a direct copy of the hw piston set up , but they have forgotten the pin, if there was a pin you would see the top of it ( it has to be inserted from somewhere) I think the splines are only there to stop the rod turning while its being assembled .
    If Diana have been economical and got rid of the pin and associated operations , and are relying on the crimp, no way is the crimp ever going to deform into the rod groove imo the pressure invoved to do this would deform the piston head .
    Easy fix is to drill a 4mm hole throug it and pin it, hw use a hardened pin , walther in the lgu use a silver steel one, both similar set ups with the same diameter rod so take your pick.

  2. #17
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    Quote Originally Posted by bozzer View Post
    Now I'm starting to doubt myself.

    Looking at the video again there is absolutely no evidence that there has been any pins in that groove on that nose of that rod. I'd expect to see something where a failed pin had started to go and some wear around that groove. There's nothing.

    I know little about pressure bonding. Could those two large pressure 'crimp' dents put enough pressure on the steel head that part of the inside diameter of the head where the rod fits in is forced into that turned groove on the piston rod? Just enough so that it holds the piston rod in place. On the wobbly pistons there's been enough wear to give some movement but not enough for that ' pressed in ' areas of the inside of the head to let go of the piston and allow it to come out.

    It's an easy option re manufacture. You don't have to accurately drill/mill holes in the head for pins or make/buy pins and fit them. You just allow one high pressure crimping action hold the piston body to the head and the head to the rod ( the latter via that turned groove ).

    PS ... I think gc93 beat me to it whilst I was typing. Well done gc93 ... that's now my favourite option.
    Now I''ve read that I may have to agree with the both of you.

    As the crimping causes the piston to go slightly out of round (and yes it does) would any out of "roundness" cause pressure points to try and force the piston back "round " and thereby loosen the effect and integrity of the crimp ?

    Given that the suggestion is that the crimp may only just retain the rod, I think this is highly possible

    I for one take these high points off on all mine so hopefully no issues
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  3. #18
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    Nick

    I don't think you would see the pin head in the case that I was thinking originally.

    I think you would drill the head and then fix the rod in the head via the splines to keep it from rotating. Then you push the pin( s ) through the head and into the groove in the rod. Then you put the head and rod assembly into the main piston body and you crimp the body to the head. So the heads of the pins would be inside the body and hidden.

    A lot of people have reported pinning theirs when they are loose. They basically do as you say and drill through and tap in a hardened pin.

  4. #19
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    We've been through a couple of scenarios here now.

    This is just what makes forums like this so very good.

    Anyone fancy sponsoring me to cut one of mine open ? Gagging to see whats in there now
    B.A.S.C. member

  5. #20
    eyebull's Avatar
    eyebull is offline Even a stopped clock is right twice a day
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    Quick Q: Is the 54 Airking using the same set-up? If so I think I'll have to sort this before I next use it.
    Good deals with these members

  6. #21
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    Exactly.

    I'm 8 days into a 21 day gut cleansing diet and I'm sitting sipping on my morning Kale, Spinach, Blackberry and Coconut milk smoothie for breakfast.

    So being involved in a bit of an engineering air rifle conundrum is keeping me sane.

    Well done chaps!

  7. #22
    eyebull's Avatar
    eyebull is offline Even a stopped clock is right twice a day
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    Quote Originally Posted by robs5230 View Post
    Anyone fancy sponsoring me to cut one of mine open ? Gagging to see whats in there now
    If we're having a whip-round I'll chip in a fiver, in the interests of SCIENCE.
    Good deals with these members

  8. #23
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    Quote Originally Posted by eyebull View Post
    If we're having a whip-round I'll chip in a fiver, in the interests of SCIENCE.
    Oddly enough I think I'd have more chance of regrowing a gonad than getting a 280 piston.
    I cant seem to find anyone that has any , here or europe so my offer may have to be withdrawn
    B.A.S.C. member

  9. #24
    eyebull's Avatar
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    Quote Originally Posted by robs5230 View Post
    Oddly enough I think I'd have more chance of regrowing a gonad than getting a 280 piston.
    I cant seem to find anyone that has any , here or europe so my offer may have to be withdrawn
    Well if you do find one, start a new thread and I'll chip in.
    Good deals with these members

  10. #25
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    Quote Originally Posted by Barryg View Post
    ... and also one of the owners of a piston that has a separated stem ( rod ) seems to be saying that the the groove in the stem ( rod ) is not lined up with the crimp on the piston body.
    From Barry's original post in this thread.

    That, plus a couple of guys saying that the crimping would not be capable of transferring pressure through to the I/D of the head where the rod/groove is.

    I just think there is plenty of evidence for the crimping does all campaign.

    They have clearly tried to keep manufacture easy here.

    If they ( me ) were going to go to the trouble of drilling/milling the head and then machining ( turning ) a groove in the nose of the piston rod in front of the splines, so that a pin(s) could be fitted through the head and into those grooves ...

    ... then why bother with the crimping. Just don't bother machining the groove in the piston and don't bother drilling/milling the holes in the head AND crimping the body to the head. Surely one would just fit the rod to the head via the splines to prevent rotation, then fit the body ... then drill straight through the body, head, rod and pin the whole lot, like other manufacturers do. Doesn't make sense to machine slot ... drill/mill head ... pin head to rod ... then crimp body to head.

    I'm defo going crimping does the whole lot.

  11. #26
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    Quote Originally Posted by robs5230 View Post
    Oddly enough I think I'd have more chance of regrowing a gonad than getting a 280 piston.
    I cant seem to find anyone that has any , here or europe so my offer may have to be withdrawn
    Chambers listing them as being available, currently. £42.35 with seal.
    Last edited by Drew451; 12-01-2018 at 11:17 AM.

  12. #27
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    Quote Originally Posted by Drew451 View Post
    Chambers listing them as being available, currently. £42.35 with seal.
    That's cheap for a Gonad. I'll have two ... mine are b*ll*cksed.

  13. #28
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    Barryg is offline Registered ̶D̶i̶a̶n̶a̶ User
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    A few more pics to look at






  14. #29
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    Come on Barry ... Duff info.

    So there's a hole in the piston body and if you look close it looks like a hole in the inside of the piston head where the rod goes in ... so back to a pin. Are they all like that or is that one that someone has DIY fitted a pin into?

  15. #30
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    It could be a swaged on lump of metal onto the stem (latch rod) and then machined for the seal area and to the diameter for the rest of the piston.

    the lump of metal will squish in around the splines and the grooved reduced part .

    Like the same machine the Smooth twists barrels were made with .

    Last edited by bighit; 12-01-2018 at 12:16 PM.

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