Monday, February 24, 2020

Some notes on a reseal & customizing a Crosman 1377

A local friend asked me to look at his 1377 which was not holding pressure. He also wondered if it could be made more accurate. Some notes on what's an established process that doesn't need great detail (disassemble, clean, reseal, assemble).

The valve assembly was crusty.

O-rings had given up any hint of elasticity.

Something new? The 1377 piston had a pin retaining the pump cup. I had not seen this before and the cups I have do not have a hole.

I can only guess that they found that the cups were popping out of the plastic retainer - possibly due to the design changing or the injection mold wearing?

I have a new ultrasonic cleaner that is almost big enough.

While parts were soaking I set about adapting a spare sight to a spare Crosman steel breech I had on hand.


Filed and formed. It's a tight fit, but slightly tighter one way t'other.

Sight mounted. It's held by two screws, one into the breech and one into the brass.

Taig now offers a 5C lathe headstock. It's a bit spendy but just the ticket for doing barrel work.

Lapping the crown. Not match grade lapping but enough to remove any burr from the lathe ops.

Finished. A longer barrel, a 760 plastic front sight and barrel band. I raided the parts boxes for this one. Friend was delighted and finds it much improved.