Eliminating Twang in Cocking Arm Spring HW97/77

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  • Eliminating Twang in Cocking Arm Spring HW97/77

    Quite a few of you guys out there would have gone through the process of tuning your Weihrauch HW97/77s to eliminate the Twang that you get just after you squeeze the Rekord trigger. Bit of time spent stripping, polishing, greasing, fitting & turning and re-assembling . The cocking action is smooth as is the entire cycle. The piston spring no longer twangs but there is still a distinctively spring resonance 'boing' on firing. It so happens that its the exact sound you heard when you disengage and reengage the cocking arm into the holder. We still have one spring to attend to.

    It's not an easy spring to get to either as the cocking arm retaining unit is held in the cocking arm via a punched nipple. For me, drilling was not an option.

    Steve Pope of V-Mach fixes stops the spring from resonating by actually drilling a hole in the arm approximately where the spring is located and injects grease into the cavity to clag the spring. The hole is tapped and a grub screw is used to seal the cavity. He doesn't recommend this practice for the DYI guys. That's me.

    I searched and found a novel way of getting grease in there without drilling and adapted it to what equipment was available to me. As I already had a 0.22 HW97K in pieces, this was as good a time to experiment.

    I had intended to attach two sound files to assist you in what you may be hearing out for the next time you shoot your 97 or 77.


    Below is the process I adopted.

    As the 22 cal HW97K was already dismantled, it was a matter of wrapping the cocking arm with copious amounts of kitchen towel and clamping it steady with father in law’s wood vice. Note the beautiful cocking aid. Airgun Wizard part #HW97K GCA (grooved cocking arm) [Matt975]

    A 5cm length of 13mm ID clear plastic tube is attached to the muzzle end of the cocking arm with a cable tie. It is clear so that we can see what was happening. Also note that the O-ring was removed before this process.

    The tube was then fill to 3 cm with CRC Molybdenum base grease which also has lithium and PTFE components.

    The original intention was to used a 5 ml syringe to pump pressurised air and push the grease through the gaps but alas, the ‘light bulb’ came on. As the OD of the syringe was approximately the same as the tube, I just used the entire unit as a plunger instead. Chopped off the pointy tip where the needle goes and Voila. Note the type of grease I used.

    Gentle and consistent downward pressure did the job. Really happy to see the level of grease dropping. Checked leakage around the cable tie, all good and with stood the pressure. As you can see from the above picture, a really thin film made its way up the side of the syringe.

    Cut cable tie, undid hosing and complete wipe down with kitchen paper. No one would have known that anything happend. Tested unclipping and clipping the cocking arm to confirm process. ALL GOOD. All I hear now is the click from the release button.

    I then decided that because it had been so successful, I started on Baby Blue 0.177 HW97K Laminate Stock. Cocked the rifle first and proceeded as per section 1 above. Airgun Wizard part not installed on this gun......yet.

    I think I have eliminated all the springy twangs that are on the two HW97s. Time to put them through their paces and have some fun.

    I hope the above info helps someone else in eliminating the dreaded Twangs.

    Believe none of what you hear and only half of what you see.

  • #2
    I can't seem to find the pictures working?