Tuesday, June 2, 2009

Disassembling an early Crosman Model 760, Part 3

As I said in the previous entry, there was a bit of an air leak around the barrel/transfer port.

One problem was that the setscrew hole in the transfer port that holds in the barrel was stripped. So I dug out some 10-32 helicoils, the proper drill and Helicoil tap.

A helicoil tap is identical to a regular one, just larger in diameter.

The helicoil, you can see a small bent tang that allows the tool to screw the helicoil into the hole.
Afterward this tang is snapped off with a pin punch.

The helicoil is inserted in the tool and the mandrel threaded on, and all threaded into the tool body. This help maintain the proper spacing/tension.

The tool is placed against the hole and the helicoil threaded in.

It was a little long...

Ground off flush with the transfer port.

There was also about .01" play between the barrel and the port diameters. So I wrapped the barrel with a few turns of teflon tape.

And poked a hole where the port is.

Assembled snug and tight. There is no more air loss here.


Josh said...

Why don't you make the transfer port/valve body channel to .140? Mine was at apprx.125- i think that would give it a velocity boost.

Felice Luftschein said...

I just wanted to get it going again. I might put a 1760 barrel on it in the future and if I do I'll mod the ports, etc.