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  1. #1
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    Hawk MK1 mainspring and fun

    Hawk Mk1 Ser. No. 21615
    Complete with .177 and .22 barrels, present from daughter. Cosmetically very good except for broken rear site. But performance was dire. I stripped it down ... the end block refused to move under spring pressure so I gingerly 'persuaded' it to move, expecting a surge as it broke free. Nope .. it wasn't moving because the spring was too weak to push it out. Spring was no longer than the cyclinder with no preload, and clearly collapsed Piston washer (ptfe) looked good, as did breech seal.
    At this point I had a Titan XS spring (No. 7) advertised as being for the Hawk Mk 1-3. From the start it was clear it was too long so I removed a few coils to give about 2" of preload. I could tell by trying to fit it that it was still too much so reduced it to 22.5cm long and 27 coils. Fitted with marked preload (about 1") but not too difficult. Firing was a marked improvement with performance about on spec, depending on pellet. But action was somewhat harsh and noisy. Cocking was OK but I could tell it was not perfect; spring had been a fair fit in the piston but I doubt if I could have fitted a piston liner.
    Then came Jim Tyler's recent AGW (August) article in which he fitted a Meteor spring as he felt the spring he had fitted was too strong. I had a Meteor spring (Titan XS again, No. 6) so stripped rifle down and fitted it. It was, again, clearly too long so needed cutting to fit to give approx 1 " preload again. I took the opportunity to make a form of spring guide ... but putting the guide in the piston, not a floating one as Jim used but a true guide fitting in the base of the piston. The guide was about 5mm shorter than the piston interior space.The end block acted as a top hat. Rifle is now much sweeter to shoot, much quieter and performs better in .177, reaching 650fps with Wasps but .22 has not changed. Just goes to show that a strong mainspring does not always equal more muzzle energy.
    While doing all this, I tested the piston for air tightness. It was good but out of curiosity I added some oil to the stock fixing holes, sealed the breech seal and pushed the piston in. Oil was expelled from one hole indicating a leak from the cylinder. I guess it was via the screwed in block but decided that I could ignore it as the stock bolt would provide a pretty good plug. I did ponder treating it as I would an HW35 but noticed that the bottom of the cylinder was profiled and that the PTFE piston seal was similarly profiled ... so I left it alone. I have come across such leaky breeches before ... the last time was a rifle where the hole for the stock bolt had penetrated the transfer port channel. But on the Hawk the transfer port channel is too far away to be 'in the line of fire' as it were.
    I mentioned the broken rear sight .. the part that incorporates the sighting notch had broken, although the main body was still present, pivoting on its pin. Remedy was to make a steel plate that I screwed and glued onto the body part ... a bit fiddly to fasten but it works. Elevation / depression is via the original thumb wheel with a spring underneath that pushes the new plate up. I do not think it has all the movement of the original but it works. The other fiddly bit is the small star washer that secures the windage screw ... I have yet to find a replacement in the same style but the old one is performing well.
    So ..... thanks Jim for the Hawk inspiration.

    Cheers, Phil

  2. #2
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    Hi Phil

    I thought I'd show you this --- I was given it by a pensioner last year while I was mending his son's JCB in his back garden (secondary developement).

    http://i1138.photobucket.com/albums/...2_05090186.jpg

    http://i1138.photobucket.com/albums/...2_05090190.jpg

    I haven't done anything with it yet, since I half expect the old chap's son to ask for it back when he finds it gone.

    I like to think it tells the story of a Father teaching his son to shoot --- and the pair of them building a case for the gun.





    I have also found the standard 20mm OD springs too tight in the piston and have used a 19mm OD Meteor spring in one Hawk.

    John Knibs now has an even better spring for both the Meteor and Hawk in spring No 11 which is 18.8mm OD and 3mm wire.




    All the best Mick

  3. #3
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    Quote Originally Posted by Phil Russell View Post
    Cosmetically very good except for broken rear site.


    I'd look for a spring around 2.9mm wire diameter, 19.1 - 19.3mm outside diameter, with between 30 and 33 coils (giving rates between 32 lbf/in and 29 lbf/in respectively) that gave a natural (without packing) preload of around an inch. That should be in the right ball park.

  4. #4
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    Quote Originally Posted by BTDT View Post


    I'd look for a spring around 2.9mm wire diameter, 19.1 - 19.3mm outside diameter, with between 30 and 33 coils (giving rates between 32 lbf/in and 29 lbf/in respectively) that gave a natural (without packing) preload of around an inch. That should be in the right ball park.
    Hi Jim

    The standard Meteor MK6 is about the nearest I can find to that spec after cutting but again the OD is only 18.8mm.

    Have you tried sleeving the Hawk transfer port down to 2.5mm yet (you'll need to use a Vulcan breach seal) ?


    I sleeved My HW35 down from 4mm to 2.3mm yesterday, the power hardly altered but the firing cycle was transformed and the chrono keeps reading dup.
    I still can't believe all that air could get through a 2.3mm hole.


    You really must try it on your Arnie




    All the best Mick

  5. #5
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    Morning, Mick.

    I think I almost certainly used a spring from an earlier Meteor in my Hawk many moons ago, and don't have the specifications, but it did suit the Hawk.

    I don't currently have a Hawk, but I understand how sleeving an over-sized transfer port can improve efficiency. I tried it on the 335, but that was before I discovered the bulge in the cylinder wall, which was effectively reducing the compression stroke to a fraction of what it should be, so the sleeving was to no avail. I really must get around to trying to cure that.

    Cheers,

    Jim

  6. #6
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    ggggr is offline part time super hero and seeker of justice
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    A couple of things here. always thought that meteor springs fit hawk pistons better than Webley ones. I took up a Hawk piston To MAG and asked for a meteor mainspring to fit. Alan, quite rightly, pointed out that it was a Hawk piston I had. I told him to try a Webley spring in the piston and then a meteor one (silver streak I think) and he agreed that the meteor was a better fit.
    I cannot understand why the Hawk mk1,2 and 3 have the same mainspring, when the mk1 has a shorter cylinder. They always seem oversprung with one of these fitted.
    On the subject of the sleeving the transfer port, I tried this after reading Mick,s comments on the B2 and the Hawk earlier this year. Not having a chrono or anything, and having a bit of time to kill one Saturday night, I found a rivet that would fit the breech seal hole on the cylinder and then put the breech seal back in. The pellet seemed to be hitting the backstop harder and the POI moved about an inch to the left and higher ( I think). I tried it on another hawk with the same result. The rivet then fell into the cylinder , prompting a quick strip down. If you are not an engineer, I suppose the easiest way of sleeving is to us some Ptfe rod or similar to make a breech seal and open up the hole a bit at a time.
    I also had the leaking cylinder thing with a hawk. I had to unscrew the cylinder end and jaws and use loctite to sort it. When chronoed for me, that had gone up from about 6.5 to 8.8ft lb.
    Cooler than Mace Windu with a FRO, walking into Members Only and saying "Bitches, be cool"

  7. #7
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    Quote Originally Posted by ggggr View Post
    If you are not an engineer, I suppose the easiest way of sleeving is to us some Ptfe rod or similar to make a breech seal and open up the hole a bit at a time.
    I also had the leaking cylinder thing with a hawk. I had to unscrew the cylinder end and jaws and use loctite to sort it. When chronoed for me, that had gone up from about 6.5 to 8.8ft lb.
    Hi Guy

    I doubt that PTFE would last very long as the hot air would erode it.

    I have been told that you can buy 4mm OD microbore brass pipe on the bay, this could be cut to length and worked in an electric drill to size it.

    I normally form the chamfered lead in by simply spinning the brass sleeve up and putting a Stanly knife blade up it --- works well.


    I wonder if the leaking Hawks could be sorted the same way as I did my HW35, with a little loctite 271 forced into the joint from inside the cylinder ?




    All the best Mick

  8. #8
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    Quote Originally Posted by ggggr View Post
    I cannot understand why the Hawk mk1,2 and 3 have the same mainspring, when the mk1 has a shorter cylinder. They always seem oversprung with one of these fitted.
    Hi Guy

    You're right again mate I've just put my MK1 and MK2 together and the MK1 has a completely different and shorter cylinder with no swelling for the breach block as the MK2 and MK3 have.

    My MK2 is an early one with the MK1 style stock, I always took it that Webley just used up MK1 stocks on the early MK2s --- but the stocks are completely different as is the cylinder and stroke (I'll try to stick a piccy up later).

    So it looks as though Jim's spring reccomendations in his excellent article on tuning the MK3 Hawk don't fully cross over to the MK1 as a shorter spring would be needed.


    Quote Originally Posted by ggggr View Post
    Cheers Mick Part of the thing I was on about was that the width and volume of the Webley breech seal should be taken into consideration in a calculation, but it looks like you have done that.
    Well while I was comparing MK1 and MK2 Hawks I noticed that the MK1s original seal has a 4mm hole through it and from the days when I used a Hawk as my main gun I vaguely remember the seal hole being fairly big and having to change it when it closed up, so perhaps they were always 4mm straight through ?





    All the best Mick

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