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Low power airsporter

Discussion in 'Anything Airgun Related' started by Meteor62, Mar 28, 2014.

  1. Meteor62

    Meteor62 Major Poster

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    Just fitted a new spring new tr Robb piston head and o ring and only achieving 7 ft lb in .177 is this all they are good for or is something wrong?
     
  2. gixxer

    gixxer Posting Addict

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    Did you check the alignment of pellet loading port in the tap?.these are oftern out resulting in damaged skirts and loss of power and accuracey.probable a little late now as it's re fitted unless you strip it again .
    generaly once stripped look down barrel whilst slowly opening rap ,what you are looking for is an equal almond shaped eye as you open it .in other words if one side of the opening isn't equal to the other it will need shimming ,I've used up to 4 shims on a mk 6 .very common.
    you can check pellet formation by shooting it into a deep tub of water so as not to dent pellet too.
    I've replaced o rings on BSA and air arms and lost fps in the process.i think sometimes they need bedding in .but it does sound low ish but I'm not sure they make full power easily.
    keep shooting it I'm sure it will pick up.i think I read an article of lubricating o rings .i have used pellgun oil on scorpions and air arms side leaver o rings which worked well but I'm not too savvy re o rings.
    it too could be pellet choice ,or tight o ring ,need for more spring pree load or even the fact the seal could have cut if the cocking slits weren't debured polished prior to install.
    Check your old o ring has the rounded edge gone flat at all.
    had Simular issue with a hi power air arms just a tight seal .
     
  3. oliver13

    oliver13 Donator

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    10 - 10.5 ftlb's is about right for an Airsporter in good nick, so they're not a powerhouse but 7 is low.
    What Gixxer said covers all the bases, there should be some shims on the loading handle side from the factory, when you check the fired pellets there should be an even shiny ring from the rifling, if the alignment is out it will be easy to see. If you do have a new 'O' ring in it will be sapping the power considerably, it's worth checking the piston without an 'O' ring on as well on old BSA's as they can expand over the years.
     
  4. SteveO

    SteveO Top Poster

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    Was the spring cut to size already or was it a full size that you've cut?

    Can you get any more coils in before it's coil bound on cocking?
     
  5. Meteor62

    Meteor62 Major Poster

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    It was a standard replacement spring from knibbs. And a terry Robb head and seal
    [​IMG]
    Will check spent pellets later for even rifling marks.
     
  6. Meteor62

    Meteor62 Major Poster

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    If I fire the rifle with the tap open should I when closing the tap feel or hear air being released? ATM it just sounds like I fired it with a pellet in it and no air released on opening the tap .
     
  7. gixxer

    gixxer Posting Addict

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    Just had a look on the net at Terry piston head kit it states it has several o rings so you can size which is better and buffer washer of different thicknesses.
    Use try the thinnest buffer and the o ring that feels loosest in the cylinder.
    If these arnt what you already fitted.
    Not a bad price for what you get.
    If you have a few washers that will fit into the piston base try a few in too to add weight and pree load .
     
    Last edited: Mar 29, 2014
  8. oliver13

    oliver13 Donator

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    It sounds like the tap is worn, there should be about half a second as the air escapes & the piston goes to rest, & if your quick you can open the tap & release it. Try putting some thick grease on & see if it's improved?

    You need to check a few fired pellets for alignment so you can rule that out, I use a bucket full of water with a hand towel folded up on the bottom. If the tap is worn it is quite a job to rectify, simply replacing the tap may not do it as the breech is probably worn too.

    It could be worse, if you had a Webley the tap is tapered so you would lose your air, & the alignment with the barrel.
     
  9. gixxer

    gixxer Posting Addict

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    I didn't know you can test the tap for leaking that way ,great idea I shall remember that and your folded towel as I never have a deep enough container of water.
    i bought a tin of ptfe spray from euro car parts ,it was a clear with a tinge of blue colour once dry in seconds.it dried quite hard and I have built up a few layers on piston internals .on inspecting shots later is doesn't appear show signes of easily being removed and air I doubt would remove it .
    i wonder if such would help reduce and gap if sprayed on to both surfaces.
    i did too spray my airs porter tap but just as a dry lube .
    i remember my old man had a grease by castrol called water pump grease ,gees this stuff was thick and firm .but I bet it's not available any more this tin must have been 40 years old.

    What does the under leaver feel like on cocking stiff or easy .
    stick with it I'm sure your going to crack it.
     
  10. Patrick

    Patrick Donator

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    NO,something is definitely wrong most Airsporter's put out about 10fpe in standard form from the factory and with a bit of fettling i.e strip down,clean and relube the muzzle energy usually increased slightly.Years ago the guy that done the air gun section for Guns Review wrote an article on basic tuning,no special parts or springs,just the O.E parts.some careful polishing etc and Abbey lubes and he was getting just over 700fps(.177) & about 550fps(.22) from a BSA Meteor.That Terry Robb piston head looks deeper than a standard one so you might be losing some volume,just a thought.
     
    Last edited: Mar 30, 2014
  11. Meteor62

    Meteor62 Major Poster

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    No I've compared it with the original head and it's actually gained some volume
     
  12. oliver13

    oliver13 Donator

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    Actually, with a big enough towel you can get away without the water, the witness marks from the rifling will be clear enough - but the towel will be somewhat stuffed...
     
  13. oliver13

    oliver13 Donator

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    I've just had a quick look inside mine which I bought a while back as fully refurbed & running well, which it was, but is still dieselling after nearly a tin of pellets.
    I find I've got an oversize 'O', the piston is a very tight fit in the compression chamber.

    [​IMG]

    Maybe the dieselling was cancelling it out but accuracy was terrible, the first shot was right on the money then the next shots were getting progressively higher & wider.
    I'll track down a smaller replacement & put it back together, with zero lube in front of the piston. I'll let you know what happens.
     
  14. gixxer

    gixxer Posting Addict

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    Now that piston head looks shorter than the one pictured earlier.or is it my eyes
     
  15. oliver13

    oliver13 Donator

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    It's modified to leave out the buffer washer & give more swept volume, you just have to redrill the hole for the locking pin, every little helps...

    In fact it may be on it's second or even third go around based on the holes it's got in it, notice the wear marks where it's contacting the cylinder wall as well, I'll take a little off it & tidy it up a bit before it goes back in.
     
  16. Meteor62

    Meteor62 Major Poster

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    You can modify the tr Robb ones and it came with instructions how to increase the volume but I don't have the tools to carry out the operation.
     
  17. oliver13

    oliver13 Donator

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    I think you just need the use of a cordless drill & the right size bit, you just fit the head without the buffer washer & drill through the existing holes in the head, but at right angles to the holes in the piston, for strength I suppose, but the pin should be free virtually floating.
    I'm not going to argue against Mr. Robb though, if you do try anything I say, for .'s sake check it first...

    Measure 3 times, cut once...
     
  18. Meteor62

    Meteor62 Major Poster

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    I have tried firing the pellets and they are not deformed at all and rifling marks are consistent all the way round. Shooting the airs porter today brought back memories from many years ago, they weren't the sweetest firing rifles of all time were they?
     
  19. Patrick

    Patrick Donator

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    Pin should be an interference fit in the piston head but a lose fit in the piston rod,if it's lose in the piston head as well it will move from side to side and could score the inside of the cylinder
     
  20. Meteor62

    Meteor62 Major Poster

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    Today I tried holding my finger over the end of the barrel whilst cocking and decocking the gun and I have to say there is no way it's leaking as my finger was being sucked in as the rifle was cocked and pushed out on the forward stroke, with sucking noises a la bike pump.
     

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