AirGunTech: Re Engineering Spring Powered Air Rifles for smoothness, consistency, and to better suit UK power levels.

HW85 Part 4, the piston and inner sleeve/rear bearing

Had a little more spare time so its onto the piston on the HW85, the spring I will be using for this tune is the Titan Xs No5, it has an OD of around 19.5mm and 3mm wire, this means I can bore the sleeve using a 19.5mm drill and it will be a nice slide fit as the drill actually leaves a 19.7mm hole.

What basically happens is I shorten the piston skirt by 4 to 5mm, in this case 4mm. I then make up a sleeve with a  rear bearing section that slides inside the piston for a glue fit. In the pics I have not machined the rear bearing section from the Acetal tube, this is done when its glued in place and I just chuck up the piston and carefully size the bearing down.

Check the pics for progress, the glue needs a day to harden fully so its a waiting game now before any more machining is done…








The 2 pics show the piston and machined sleeve, its a snug slide fit and is washed/degreased along with the piston prior to gluing in place.


  Here we have the piston skirt, I did not do a before/after shot here, all that is done is 4 to 5mm is take off the skirt, this has to be done very very carefully and slowly as the skirt is induction hardened to form a bearing.






Next up the bearing glued into place…I use Industrial super-glue along with a Loctite activator for metal to plastic, this has proven pretty much bomb proof as long as you give the glue time to harden properly.

Once hard the new plastic skirt is machined down to 5mm  height and the OD reduced to a nice glide fit in the rifles compression tube, the inner edge is rounded slightly and polished with 320’s so the spring will not bind on it.





Next to machine after this is the front TopHat bearing and slipper washer then size the spring….hopefully the rifle will be under test by the weekend.








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