Page 1 of 2 12 LastLast
Results 1 to 15 of 21

Thread: More woes with my sumatra carbine :-(

  1. #1
    Join Date
    Jan 2011
    Location
    Swansea
    Posts
    3,973

    More woes with my sumatra carbine :-(

    After tinners advice when my sumatra power locked last year i bought a predator hammer spring. After reassembly the gun was down on power but i knew how the adjust it to get the power up as it was only 9ftlb in the chrono but could not be arsed to stip it again so just used it for garden plinking fun. Gun had been working ok up until i last used it 3mths ago. Today pulled it out to use and the bugger is not firing again. Feels like it is power locked again. But why though as the pressure om rifle guage is on 190 bar which is fine. The hammer spring is not that old either. Plenty of heft in the spring as the gun is heavy to cock compared to the standard spring. Is this a common fault on the 707/sumartra rifles? At a loss what has caused this to happen again.

  2. #2
    Join Date
    Feb 2012
    Location
    gateshead
    Posts
    12,116
    not good mate,i hope some one on here can help you out

  3. #3
    Join Date
    Jan 2011
    Location
    Swansea
    Posts
    3,973
    Quote Originally Posted by rapidresponse1 View Post
    not good mate,i hope some one on here can help you out
    Cannot understand it mste. The predator springs do not corrode so it cant be that. It was working a few months ago. Spring is plenty strong enough as it has been a bugger to cock as this spring is harder than the last.

  4. #4
    Join Date
    Apr 2002
    Location
    Near Wimbledon, SW London
    Posts
    22,193
    take the stock/ shroud off, remove end cap and spring, check power adjuster is not buggered.. or just unscrew the course threaded collar and remove. if it still won't fire get a large puch and a small hammer and the tap the vale stem directly.
    I'm currently looking for: pair of scope mounts to suit a 13mm BSA rail, a tx200 cd trigger unit top sear, and any cheap, interesting, knackered project guns. Thanks, JB.

  5. #5
    Join Date
    Jan 2011
    Location
    Swansea
    Posts
    3,973
    Quote Originally Posted by Shed tuner View Post
    take the stock/ shroud off, remove end cap and spring, check power adjuster is not buggered.. or just unscrew the course threaded collar and remove. if it still won't fire get a large puch and a small hammer and the tap the vale stem directly.
    If it is the valve stem what could have caused it to happen? Maybe it was not the hammer spring last time then jon? Would fitting the uprated valve stem cure it if it is the valve stem jon?

  6. #6
    Join Date
    Apr 2002
    Location
    Near Wimbledon, SW London
    Posts
    22,193
    need to see what the problem is first.

    if the valve stem is getting stuck, it could be the profile of the mushroom head, somehow settling into and jamming into the valve face itself. But that would be unnusual, unless it's been previously modified, or made from a dodgy batch.. the material is delrin like. Maybe it could save some grease of something sticking in there ? Or an excessively heavy valve return spring. It's quite weird.. see if a few taps frees it up first.

    Then again, maybe it could be as simple as a bent stem.. trouble is, if the stem was that bent, I wouldn't expect the head to seal. and those stems are thick / heavy duty as standard.

    Puzzling.
    I'm currently looking for: pair of scope mounts to suit a 13mm BSA rail, a tx200 cd trigger unit top sear, and any cheap, interesting, knackered project guns. Thanks, JB.

  7. #7
    Join Date
    Jul 2004
    Location
    cardiff, south wales.
    Posts
    3,105
    Is it possible that something has come adrift at the valve return spring end, a strip down seems the only way to get to the bottom of it in my opinion.

    John
    Law of any kind only affects those willing to abide by it.

  8. #8
    Join Date
    Jan 2011
    Location
    Swansea
    Posts
    3,973
    Quote Originally Posted by Shed tuner View Post
    need to see what the problem is first.

    if the valve stem is getting stuck, it could be the profile of the mushroom head, somehow settling into and jamming into the valve face itself. But that would be unnusual, unless it's been previously modified, or made from a dodgy batch.. the material is delrin like. Maybe it could save some grease of something sticking in there ? Or an excessively heavy valve return spring. It's quite weird.. see if a few taps frees it up first.

    Then again, maybe it could be as simple as a bent stem.. trouble is, if the stem was that bent, I wouldn't expect the head to seal. and those stems are thick / heavy duty as standard.

    Puzzling.
    I changed the hsmmer spring to a predetor heavy duty one last year as fitting a heavier hammer spring fixed this problem on tinbums gun as it had the exact same problem but makes the gun a bugger to cock. Has been working fine up to now. Am i right i. thinking the hammer runs dry as in all other pcp's jon? Is it the hammer or valve face delrin jon as you confused me a bit. Chris

  9. #9
    Join Date
    Jun 2010
    Location
    leeds
    Posts
    465
    Could it have had the valve messed with in the past and now it takes a real heavy spring to open it and the transfer port is doing itís job of restricting the power back down to sub 12 levels?

  10. #10
    Join Date
    Apr 2002
    Location
    Near Wimbledon, SW London
    Posts
    22,193
    the valve is steel. the hammer is steel. the mushroom head on the valve stem is synthetic (delrin ?), encased in brass. the (inner) valve face is steel.

    so the only way it cannot fire is if the valve stem delrin mushroom is not being knocked away from the sealing face of the valve. generally, the only things that hold it in place are air pressure (hence you pressure lock situation) and the valve return spring.

    this is why I suggested the power adjuster (which limits and can block) valve stem travel be checked first.
    I'm currently looking for: pair of scope mounts to suit a 13mm BSA rail, a tx200 cd trigger unit top sear, and any cheap, interesting, knackered project guns. Thanks, JB.

  11. #11
    Join Date
    Jan 2011
    Location
    Swansea
    Posts
    3,973
    Quote Originally Posted by rovercoupe View Post
    Could it have had the valve messed with in the past and now it takes a real heavy spring to open it and the transfer port is doing itís job of restricting the power back down to sub 12 levels?
    Gun has not been messed with i know that.

  12. #12
    Join Date
    Jun 2010
    Location
    leeds
    Posts
    465
    Hmm,just a thought but does it have a plastic restrictor on the valve stem? Could this have swollen and itís stopping the hammer from getting to the stem?

  13. #13
    Join Date
    Apr 2002
    Location
    Near Wimbledon, SW London
    Posts
    22,193
    Quote Originally Posted by rovercoupe View Post
    Hmm,just a thought but does it have a plastic restrictor on the valve stem? Could this have swollen and itís stopping the hammer from getting to the stem?
    or somehow jammed.. yeah, good point.
    I'm currently looking for: pair of scope mounts to suit a 13mm BSA rail, a tx200 cd trigger unit top sear, and any cheap, interesting, knackered project guns. Thanks, JB.

  14. #14
    Join Date
    Jan 2011
    Location
    Swansea
    Posts
    3,973
    Quote Originally Posted by rovercoupe View Post
    Hmm,just a thought but does it have a plastic restrictor on the valve stem? Could this have swollen and itís stopping the hammer from getting to the stem?
    What does the restrictor look like as i hsve no idea what i am looking for.

  15. #15
    Join Date
    Jan 2011
    Location
    Swansea
    Posts
    3,973
    Quote Originally Posted by Shed tuner View Post
    or somehow jammed.. yeah, good point.
    I have removed the hammer before. How do i get to the valve stem jon? Is that restrictor on the valve stem or the valve?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •