was fooling around with a couple of PC77 Crosman Pump pistols,
and as I was looking over a valve I noticed there was some
flash remaining from a driling/reaming operation at the factory.
took the valve apart and decide to try a couple of things
to make it easier to pump and perhaps increase the power a
profiled the valve head to offer less shrouding of the valve
trimmed down the inlet valve to give a bit more internal volume.
flash in the port was removed and a new port angle reamed
with a 1/8" end mill.
a bit off the end of the valve body inlet to try to use the
air that is trapped between the parachute seal and the valve
body tip. Careful here ... too much and the pump arm will
flop upon firing. (I think a better way to achieve the same
result would be to drill tiny holes fron the sides of the
inlet cone through to the inlet hole.
assembly, I replaced the valve spring with one from a 2240
and stretched it out a bit. The softer spring makes it easier
to "crack" the inlet valve while pumping, but the
gun must be "half-cocked" to be pumped.
.... Much easier pumping, and less noisy....
PC77 will get a new TKO design flat top pistol ... (zero headspace,
with minimal space between valve sealing o-ring and piston