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cyberfish2 · Member

I'm rebuilding my Gamo Whisper. It's getting a GRT-III triger, a Crosman
Nitro Piston, and a new piston seal. I've honed the piston cylinder to remove the sharp burr(s) that damaged the original seal, and removed the
seal after heating it with a hair dryer.
What's the best way to get the new seal over that tapered boss that retains it? Also, should I use a thin shim to shield the long slots when I slide the new seal in place?
I'm new at this, and don't want to damage the new seal.
Ok, 2nd question: If I vary the preload on the new Nitro Piston by making a .xxx long spacer, will that adversely affect performance, or just change the FPS and cocking force? I suspect some of you have already tried this with springs?

SMP · Silver Status Member

LOL...Bottom to top

Preloading a gas piston wont give you any benefit. It's force is almost as high at the end of the stroke as it is in the middle.

Usually it is beneficial to debur the inside of the slots almost to the point of a radius profile. If you do that then you will only need to push down the lip of the piston at the end of the slot.

For putting the seal on I think the best way is a short soak in very very(near boiling) hot water. Then they just pop on. Put a thin coat of silicone oil on the seal area of the piston to allow the lip to slide into position