STEP 9 AND 10.
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.