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Thread: HW90 Issues

  1. #1
    Marksman

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    Default HW90 Issues

    I recently bought a second hand HW90. It looked in excellent condition but on closer inspection there are a few issues I need to sort out and Iím hoping someone can point me in the right direction.

    On first inspection I noticed a few small, possibly insignificant issues.

    1. Small locking screw on front trigger guard missing
    2. Valve covering screw and o-ring missing
    3. Metal scraping sound when cocking.
    4. Tiny screw inside actual trigger blade missing (not bigger screw directly in front of trigger)


    First issue I have, trying to cock for first time, sear wonít latch. I discover that the safety button is either in or out (not sure which way around it was), pushed it in, gun latches. After taking a few shots with it, I noticed that it was a little under powered @796 fps with JSB exacts 8.44gr which is around 11.88 fpe. I took it into a gun shop for it to be pumped up a little. Settled on 921 fps around 15.90 fpe. Shoots very nicely at this speed.

    On Saturday I decide to inspect why there is metal scraping when being cocked. The two screws on either side that hold the gun to the stock are quite loose. The large screw that holds the trigger guard that should have the small locking screw is also quite loose. Remove stock and I notice some light scuffing under the cocking lever. I do a google search and find an exploded diagram that shows there should be a plastic glide on the lever. Iíll have to either fashion one out of something or order it off the site I found with the exploded diagram (https://www.gunspares.co.uk/products/24574/HW90 for those who are interested, they keep all the little bits I need).

    When I put the rifle back together I tighten all screws that were loose. Try cock gun, very difficult to break barrel, also wonít latch again. Loosen two front stock crews and the breaking is immediately easier. Push safety button (which is now extremely hard to do) and eventually get it latch. Try pull off a shot but trigger wonít release sear, I can pull it all the way back but thatís it.

    I decide to take gun apart again but as Iím loosening the front trigger guard screw, the sear releases and a wild pellet shoots into the wall next to me! So I realise this screw needs to be looseÖ.can someone explain to me why please, apologies if this is a dumb question? Also, why do the two front stock screws need to be loose so that it doesnít make the barrel impossible to break?

    I have put it back together again and will order all the little bits missing, if anyone knows where I can get these parts locally Iíd appreciate it, otherwise I will order off the UK site, not ridiculously expensive.
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  2. #2
    Sharp Shooter

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    Hi Barman,

    I think the cocking/latching/front stock screw issues are due to the missing plastic glider BK073.
    Attention please - this piece will certainly get broke if you try to cock the gun out of stock.

    So I suggest you to get the parts firstly (I bought from Chambers for my own HW90 project to my full satisfaction) and get them installed.
    Then come back here anyway.

    Concluding from your comment you don't have problems loosing air pressure.
    If you're going to order from Chambers anyway I'd reccommend to order the following parts right away to have them ready for future service of the GasRam:
    OR066 / OR070 / PW128 / PW129

    Please take care for proper refitting of trigger guard!

    Here some links for more information - hopefully helpful:
    ARF Library: HW90_Gas_Ram_Removal
    hw90 - Weihrauch Owners Club
    hw90 strip-down-guide for ya'll ...

    I have done a little strip down guide for the hw90. There are a couple of things 'amiss' so to speak..... 1/ the rearmost trigger guard screw on mine is non standard [so dont be alarmed if yours looks different]... and 2/ i have modded my inertia weight a little, so again it will look different to your own,,,,,, all other aspects are the same.

    first up> grab your hw90 and prepare some work space, remove your scope if one is fitted>

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    now remove the stock screws, 2 up front>

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    remove trigger guard screws, the tiny one is actually a "lock bolt" to stop the big one vibrating loose...... you will see>

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    trigger guard off >

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    now the action will lift out of the stock [yes my stock is different, i ghost-blacked the inletting, and made a nice recess/fastener to tidy-up an old sling-hole >

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    now remove this pin, its the trigger assembly retaining pin >

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    voila, trigger unit slides out rearwards >

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    now undo the little grub screw in the rear block [this locks the main locking bolt in situ] >

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    here it is removed >

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    now the main retaining bolt/pin is free to come out, but FIRST we need to de-pressurise the ram, so undo the upper-most screw and inside lives the schrader-valve >

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    gently tap the end of the valve with a punch or similar, you will hear the air escaping >

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    NOW that main pin can be removed >

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    next tap the pivot-pin out of the front of the cocking-arm , and slide-out the cocking arm and its shoe >

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    remove the ram and piston [most likely the rear-ram will come out, then you will need to get the piston out after [use an allen key in the cocking slot to push the piston out>

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    next remove the nylon scraper ring and the 2 o-rings from the rear of the piston body then you can withdraw the inertia weight [i tap on the rear of the piston with a rubber mallet until the weight is all the way to the rear, then fish it out with a small hook-tool inserted down the central port-hole >

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    heres me modding the inertia weight >

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    the inner-nose of the piston is recessed further forward than the outer head...... this means that when the inertia weight is in the forward-most position within the piston, it is actually 14.5mm away from the inner face....... so i drilled/sleeved/thread locked some tube [i drilled it to 3.2mm internally the same as stock bore ID] and loctited it inside the [drilled to accept] inertia weight hole with 14.4mm protruding ...... i then ported both end of the "transfer-tube" to smooth airflow during transition....... the main idea being that should the weight ever hit the end of the piston this protruding port-tube will act as a buffer to 'choke' the final few mm of travel, thus giving a softer "slam" >

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    heres the inside of the piston with the end-most recess i was describing >

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    now then, time to rebuild, no point showing the same pics in reverse, just put it back the way it came apart ....... i use a blob of rubber grease on my fingers and "fondle" all o-rings prior to insertion....... then i mix some 'molyslip' with some good engine oil and squirt 2-3ml inside the ram to slosh around keeping everything smooth ... refit the piston [ive fitted the new style Weihrauch seal] , then refit cocking arm / its pin / the ram / ram retaining pin / its locking grub screw / trigger unit and its retaining pin >

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    now its time to pressurise the ram , i like to do it before stock re-fitting as it will push the piston forward for you as you pump, and the piston need to be in the forward position in order to 'cock' the trigger, in order to fit the trigger-guard >
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    i fill mine to about 200 ish psi as a start point , [once the stock is fitted you can tap the valve again to drop the pressure a bit at a time until you arrive at your chosen power/fps] >

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    refit the trigger unit and its retaining pin [note the position of the safety latch in its natural position]>

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    now 'cock' the trigger safety latch into the forward position [this is necessary in order to allow the guide to locate properly later] >

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    sit stock over the action >

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    now place the trigger-guard in position...... you will need to push the safety-button about half way in to let the guard "sit down" >

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    also you will likely need to push the trigger-blade rearwards a little >

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    replace all stock-screws and squeeze the trigger to uncock it , here's the new breech seal [easiest to do this when the ram was depressurised, no risk of anything nasty happening] >

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    now shoot a good few pellets over the chrono, and remember to gently tap the valve to drop pressure if needed >

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    re-fit the schrader-valve-cover-screw not forgetting its little o-ring seal now wipe clean your pride and joy and re-fit scope etc........ >

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    some points of interest.....
    the new style piston seal is good, more efficient than the old style once bedded-in, i'm noticing fps variations have dropped to almost single figures and that 'mod' i did to the inertia weight is good too....... i have a feeling that this mod is not only making the final bit of inertia weight travel 'softer' but may also be contributing to the single figure fps readings . maybe some of the improved feel is the new o-rings, the new piston seal or the inertia-weight-mod ive done, ive changed too many variables at once to be 100% conclusive.. but........ whatever is happening is all-good, the shot cycle is maybe a tiny bit faster [due to new style piston seal] ...... but the recoil is a little softer , win-win.

    Good luck.
    Andy
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  3. #3
    Marksman

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    Thank you pelletcaster, appreciate the response.
    Tony
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  4. #4
    Sharp Shooter
    WP HFT/Springer Champ '15

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    I know Jacowp is very good with HW90s. Try him
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  5. #5
    Marksman

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    Quote Originally Posted by Mr H View Post
    I know Jacowp is very good with HW90s. Try him
    Thanks, I have mailed him
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  6. #6
    Marksman

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    Anyone have any advice on removing the cocking arm pivot pin? The only info I can find is to knock it out, mine won't budge though. Is there a specific side or does it come out from either side. I'm scared to bang it too hard and destroy something!
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