Airgun World - - Fettling The Hw57 -

Mea­sure out the length you need – in­ter­nal length of pis­ton. Next, mea­sure the in­ter­nal di­am­e­ter of the pis­ton, and mul­ti­ply by three. This will give an ap­prox­i­ma­tion of the width, al­though you will need to fine-tune this a bit.

The thin metal can be cut with kitchen scis­sors – be­ware of the sharp edges. When you have the right size, cut some V-shaped notches at one end, bend them over, and this will help to an­chor the liner in place.

The liner can be rolled around the spring

and pushed into the pis­ton. Al­ways make sure the gap in the liner is op­po­site the slot in the pis­ton.

It is likely that the guides will come with a washer to drop in­side the pis­ton to an­chor the liner and form a bear­ing sur­face for the top hat.

It is al­ways worth smooth­ing any burrs or rough edges. These are par­tic­u­lar­ity preva­lent in the cock­ing slot and the end of the cock­ing shoe. En­sure that you clean and flush out with de­greas­ing spray.

Whilst apart, it makes good sense to check the pis­ton seal. Any dam­age to the lead­ing edge around the cir­cum­fer­ence will con­trib­ute to air leak­age and hence lack of per­for­mance. Re­moval is a mat­ter of lev­er­ing off with a wide-blade screw­driver, and hot water can make things more pli­able.

Re­assem­bly is the re­verse process; lu­bri­cate spar­ingly, a smear of moly paste on the edge of the pis­ton seal, a lit­tle on the pis­ton skirt. A very small amount of moly grease may be ap­plied to the spring.

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