TO CONSTRUCT THE LINER:
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.