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Thread: just upgraded my leather HW35 to synthetic...

  1. #1
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    just upgraded my leather HW35 to synthetic...

    I should say first up, that mine had the small (2.9mm) port. If yours has the larger (3.5mm+) port, this may need sleeving.

    I machined a shoulder on the piston face to form the reduced diameter section for the synth seal's shoulder to sit on. Then I machined up an ally disc approx 24.5mm dia 3mm thick to form the "mushroom button" that retains the seal. trimmed off the M8 threaded piston rod to suit, threaded on the mushroom with a bit of loctite, job done. The stroke is extended by 4mm (I could have squeezed 5 before hitting cocking slot issues, but 4 was easier). I grabbed a tatty used Hw80 seal from the parts bin and sized the rear edge down a tad (leaving the front lip untouched).

    Before starting, power was bang on 11 FP with leather... with this setup, I had to remove 2 coils to get it legal, back to 11.4. Importantly, it is so much smoother - because it is less snappy - and it has a better air cushion (no doubt also due to the stroke increase). The reduction in preload also means the piston is more cushioned in it's landing. It was quite nice before, but this has transformed it.

    Thoroughly recomended if you have a small port (or can sleeve it).

    HTH - JB
    Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.

  2. #2
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    Top result and excellent information, JB.

    They really are nice, aren't they?

    My old "war dog" of a '35, a quite nasty looking thing cosmetically and bought for £30 ten years ago shoots beautifully. It has the Knibbs convertor, so will probably have an even shorter stroke than standard and V-Mach spring, top hat and guide and is very, very smooth. Bet it's not as nice as yours, though, as it still runs the larger diameter TP.

    Mick has also posted in the past detailing fitting the later factory piston intended for the synthetic seal. So, for those unable to perform the work involved or having no access to a friendly engineer, fitting the later piston enables the use of the synthetic seal (obviously), increases the stroke (4-5mm I think) and is also lighter.

    Love the 35. An old classic design with excellent barrel lock up, superb trigger and excellent balance, especially on opens. Not daft money new and often available at positively bargain prices secondhand.

    Day off tomorrow......hoping to get the war dog out!
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  3. #3
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    '35

    Informative post there shed-tuner. I've long been an advocate of swapping from leather to synthetic (but not in the way some people think)
    As Walter eluded to in his airgun book you have to wonder what the Original 45 could have been capable of back in the day had M&G not had a rush of blood to the head and fitted the guns with leather piston heads. As mentioned above with the HW 35 you can pick up the steel converters to swap over but your work here seems even more productive. Like you I've always thought along the lines of reducing spring input after swapping from leather to make the most of the more efficient seal. You've demonstrated it admirably here. I do wonder if this also brings benefits of reduced wear (to a degree) since cocking effort and strain on pivot points is reduced slightly.
    I know there are guns that perhaps it's best to stick with the factory leather particularly when needing to keep a collectable gun 100% original, and of course there will always be those who would class you as a heretic for swapping to synthetic. But from my experience it pays dividends in the vast majority of cases.
    Again, thanks for the informative post.
    Dave
    Last edited by jonnyone; 13-07-2019 at 08:53 PM. Reason: Typo

  4. #4
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    A few have also used 'O' rings to very good effect.

    I have had the absolute pleasure of trying a few thus converted by Mick, T20, and they have all, without exception, shot beautifully.
    THE BOINGER BASH AT QUIGLEY HOLLOW. MAKING GREAT MEMORIES SINCE 15th JUNE, 2013.
    NEXT EVENT :- May 17/18, 2025.........BOING!!

  5. #5
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    Good read. Thanks for sharing. Which calibre please?

  6. #6
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    cheers chaps...

    It's a .22 E - if you had a .177, this is defo the way to go to get 11+

    Incidentally, I see a synth sealed piston on the bay right now - a good drop in replacement (sale is not mine, but I think it may be a chap on this BBS).

    The 4-5mm stroke makes for a lot of extra air on a 30mm comp tube, plus the reduced friction and enhanced sealing.
    Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.

  7. #7
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    I haven't looked on "that" sales site, Jon, but even new from Chambers they're excellent value......£35.60 for piston complete with seal. Bargain!
    THE BOINGER BASH AT QUIGLEY HOLLOW. MAKING GREAT MEMORIES SINCE 15th JUNE, 2013.
    NEXT EVENT :- May 17/18, 2025.........BOING!!

  8. #8
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    Quote Originally Posted by TonyL View Post
    I haven't looked on "that" sales site, Jon, but even new from Chambers they're excellent value......£35.60 for piston complete with seal. Bargain!
    yeah, that's decent value for the benefit. Esp if you sell the old one inc leather for £15-£20.
    I think the one on the bay was about £30 all inc (used).
    Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.

  9. #9
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    Quote Originally Posted by shed tuner View Post
    yeah, that's decent value for the benefit. Esp if you sell the old one inc leather for £15-£20.
    I think the one on the bay was about £30 all inc (used).
    sportswaffen €24.50 + p&p

  10. #10
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    Quote Originally Posted by CapitalBee View Post
    sportswaffen €24.50 + p&p
    Nice.
    THE BOINGER BASH AT QUIGLEY HOLLOW. MAKING GREAT MEMORIES SINCE 15th JUNE, 2013.
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  11. #11
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    Sunday didn't happen but today did.

    A lovely little session at ten yards down the garden. Open sighted simple, springer pleasure.

    Love this old gun.

    Just realised that it's actually about 11 years since build, so might treat the old girl to a strip and relube soon.

    Any maybe the later piston?
    THE BOINGER BASH AT QUIGLEY HOLLOW. MAKING GREAT MEMORIES SINCE 15th JUNE, 2013.
    NEXT EVENT :- May 17/18, 2025.........BOING!!

  12. #12
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    I would like to try this mod on my 1977 Hofman Premier

    Hi

    I have bought a synthetic seal piston assy to put in my hw35. I had opened to 4.0 mm (silly me!)
    I was never happy with the results as it never felt right. I then went back to leather.

    I am now tempted to do this modification and I am prepared to insert a piece of brass tubing to reduce the port to 3mm
    I am not too sure about what you said: "trimmed off the M8 threaded piston rod to suit" . Do you unscrew the rod to cut it shorter? I have access to a lathe.

    Thanks

  13. #13
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    nah, when you unscrew the piston washer and holder, you get an m8 threaded rod sticking out. if you machine back the shoulder of the piston face, to increase the stroke, as i mention above, leaving the central section around 22 mm fo fit inside the tighter section of the seal, then screw on a machined ally disc 3mm thick to form the mushroom that retains the seal, around 6mm of that m8 rod will be left pocking through... just chop it off flush.

    i did take a piccy, will post in up over the weekend.

    defo sleeve down the port.. just loctite the tube in.
    Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.

  14. #14
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    Quote Originally Posted by Shed tuner View Post
    nah, when you unscrew the piston washer and holder, you get an m8 threaded rod sticking out. if you machine back the shoulder of the piston face, to increase the stroke, as i mention above, leaving the central section around 22 mm fo fit inside the tighter section of the seal, then screw on a machined ally disc 3mm thick to form the mushroom that retains the seal, around 6mm of that m8 rod will be left pocking through... just chop it off flush.

    i did take a piccy, will post in up over the weekend.

    defo sleeve down the port.. just loctite the tube in.

    I do it a bit differently, Jon.

    I measure the stroke and cocking lever gap and do a quick calculation before I start machining.

    Then I machine the front of the piston back by the amount needed to end up with a 71mm stroke, naturally this leaves more of the latch rod exposed.

    After threading the newly exposed latch rod I screw on an alloy or delrin arbour to take the synthetic seal.

    A quick tickle with a Dremel on the rear of the cocking lever slot in the piston to give a 1mm clearance on the cocking lever and it's good to go.


    Doing it this way removes more weight from the piston and gives more threads inside the arbour, but saying that, this still doesn't get the piston down to the weight of the factory synthetic sealed piston.





    All the best Mick

  15. #15
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    Quote Originally Posted by T 20 View Post
    Doing it this way removes more weight from the piston and gives more threads inside the arbour, but saying that, this still doesn't get the piston down to the weight of the factory synthetic sealed piston.

    All the best Mick
    yeah, I get you.. I was slightly worried about only 3mm of threads in there, but then again, it's not really under any force. What is the weight of the factory synth piston ? I reckon I probably only saved 10g max over std leather.
    Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.

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