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Thread: hw77 piston sleeve help

  1. #1
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    hw77 piston sleeve help

    Just gave an old 1986 hw77 what seems to have been it's first service, anyway its now back from the dead and shooting nicely it's just got a bit of a twang so was thinking of making a piston sleeve to help quieten it a bit.

    Could anyone tell me the size to make the sleeve? I have a sheet of shimming material so can easily use that.

    Thanks!
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  2. #2
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    Have you fitted new top hat and spring guide?

  3. #3
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    Fitted a spare nylon top hat but using the standard spring guide. it seems a good fit for the spring i used which was shorter than the original. It's putting out just under 11 ftlbs and has quite a nice firing cycle, much better than what it used to be, it's just the twang that needs taking care of.
    I just don't know the best size and length of sleeve to use?
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  4. #4
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    is the original guide metal? normaly the bulk of the twang is down to the guides, iv never looked inside a 77 but coincidently im due to pick one up this weekend to restore/tune.
    I generaly fully sleeve the piston so i cut the material about 5mm longer to allow a bit to fold under the top hat to hold it in place and i use the thickest material i can fit between spring and piston wall

  5. #5
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    Try this: I have fitted sleeves to many '77s.
    MAKING A PISTON LINER

    Piston liner; I do not have dimensions but here is a quick guide to how I make them: Empty beer can, tall type i.e. taller than the piston is long. Cut sides off to form a sheet. Make sure sides and ends are square to each other. Get sheet of paper and roll into a tube ... put in piston and mark where sides overlap and the correct depth of the piston. Measure and transfer measurements to the steel sheet. Cut sheet but add 5mm to the length. I now have a bit of plastic tubing that fits over the piston rod but goes inside the piston. Roll the sheet around this tube and insert into the piston, but not all the way: leave about an inch out as you need to remove the sheet in a minute: Mark the sheet if the sides overlap. Remove and trim to size so the sides do not overlap. Now mark a line 5mm in from one end and cut crenelations (beautiful word that, fancy word for tabs) along the end and down to the line ... I use ordinary scissors for the cuts. Cut out every other tab out so the end looks a bit like a castle battlement. Put sheet around plastic tube again and fold the tabs down 90 degrees. Place tube and sheet into piston with the join away from the piston linkage slot. Push to bottom of piston, remove plastic tube. I now add a steel/delrin washer inside the piston to sit over the tabs. Add this and push into place with the mainspring. Job done.

    You could of course ignore using the paper sheet and go straight to using the steel sheet for the first measurement ... but you may still need to make a fine adjustment for the final product.
    And you get to drink the beer.

    Cheers, Phil

  6. #6
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    I've made two in the last few weeks using Phils method and it works well. Unfortunately I used PTFE sheet instead of steel and the spring has eaten one and I need to check the other. I'm gonna replace them with steel if I can find someone to drink the beer for me?
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  7. #7
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    I thought hw's had piston liners as standard? Seems daft putting another steel sleeve inside.

    Most of the twang will be from the guide imo.
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  8. #8
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    Quote Originally Posted by p.sharp View Post
    I thought hw's had piston liners as standard? Seems daft putting another steel sleeve inside.

    Most of the twang will be from the guide imo.
    Nope, sleeve not standard. Well worth doing. Its primary purpose is to stop any lube from migrating towards the compression area, but its secondary benefit is to reduce twang slightly.

    I would agree that reducing twang is more down to properly fitting spring guide and top hat. If this rifle has the old metal one, you could switch that for the later, nylon one. This will reduce twang. However, custom fitting ones will make it even better.

    You could buy a different spring with matching top hat and guide, but then if you have recently forked out on a new spring, you may be reluctant to spend again.

    If you took the exact ID measurements of the spring, I'm sure UK Neil, Bigtoe or Welsh Willy would be happy to oblige.....Assuming here that you haven't the facilities to turn your own up.
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  9. #9
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    Thanks for the replies, I will have a go at making one as Phil describes and see how it goes.

    The guide fits the spring quite well, it's not loose at all but doesnt seem too tight. It goes on with a bit of a push so Im not sure how it could be responsible for the twang? hopefully this will sort it though. Thanks again for the help!!! and cheers TonyL for the names, if this doesnt work Ill see about getting some guides made up.
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  10. #10
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    Quote Originally Posted by tinbum View Post
    I've made two in the last few weeks using Phils method and it works well. Unfortunately I used PTFE sheet instead of steel and the spring has eaten one and I need to check the other. I'm gonna replace them with steel if I can find someone to drink the beer for me?
    I did try 0.5mm ptfe (I think) once in a 25mm piston 77 but found that the spring was too tight a fit on the ptfe ... it would just fit the spring with a bit of a push but I felt it would get too tight with a compressed spring. So I reverted to a 'beer can' or maybe it was a coke can, liner. I have never had one fail me yet.
    Cheers, Phil

  11. #11
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    ohhh BTW, carling cans are steel and not ali. Just thought Id mention that as have just checked
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  12. #12
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    I recently tuned a HW 35 , i found that a standard HW80 liner with the length cut down fitted a treat, anyone know if the same would apply with a 77?

  13. #13
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    80 and 35 employ a 30mm bore, 77s will be either 25 or 26 so, in standard form, no, it will be too wide.
    You could cut it to suit, but if you're having to trim both the length and the width, maybe as well to make one yourself using Phil's tips.
    Alternatively, I think Knibbs will sell a ready to fit one, but won't be cheap.
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    Mylor is good to try,and robust.
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