STEP 9 AND 10.

Airgun World - - Fettling The Hw57 -

This is when we in­spect the com­po­nents and rec­tify is­sues that con­trib­ute to­ward vi­bra­tion and un­due noise.

Check the fit be­tween the main­spring and its guide, like­wise the fit be­tween the spring and the in­ter­nal part of the pis­ton. Do ei­ther ap­pear loose, with too much clear­ance?

If the an­swer is yes, it will ben­e­fit from some cor­rectly fit­ted cus­tom-made parts.

We need a spring guide which is a close fit in­side the spring with­out be­ing overly tight. The ad­di­tion of a front guide or ‘top hat’ will also help to keep the spring straight when un­der ten­sion and help it to turn eas­ily when be­ing com­pressed.

If there is ex­ces­sive clear­ance be­tween the spring and pis­ton, it is worth look­ing at a pis­ton liner, which ef­fec­tively fills the small gap be­tween spring and pis­ton, re­duc­ing vi­bra­tion; not only that, but it will also stop grease mi­gra­tion from the main­spring. Any grease get­ting in front of the pis­ton seal will re­sult in diesel­ing – com­pres­sion ig­ni­tion of oils.

It is un­likely that many of us have metal turn­ing lathes, which is the re­quired tool to en­gi­neer the new spring guides. Typ­i­cally, these are made of Del­rin – en­gi­neer­ing grade syn­thetic ma­te­rial – and thank­fully, many In­ter­net-based com­pa­nies of­fer a ser­vice whereby you send your spring and they will en­gi­neer a per­fectly fit­ted guide for a rea­son­able sum of money. I know a lo­cal airgun en­thu­si­ast who pos­sesses the nec­es­sary equip­ment, and skill, and was able to turn a guide set out in record time. Thanks, Shaun.

The pis­ton liner is eas­ily fab­ri­cated at home by us­ing an empty drinks con­tainer. I would rec­om­mend us­ing a steel can rather than alu­minium be­cause it will be more hard­wear­ing. If in doubt get a mag­net out to check.

9 10

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