Canadian Airgun Forum

Well, I don't know if anyone still plays with these old crosman guns anymore. One of my favorite pastimes from years gone by (lol I'm gettin old), is modding pellet guns.
I think Doug would have liked this one. Though I'm sure he has had many tricked out airguns through the years.
The plan is to take a crosman 140, run a 1377/2289 valve, in .177, have it shoot around 900 fps with 10 pumps or less.
What do you boys think? Can it be done?
We will see.

Sounds like a project that needs lots of pictures.

Phase 1 or 2 rear cocker seems a natural if you have the parts...what were you planning to do for a trigger?

Al

Besides the difference in valve sizes, there is also the different trigger setup. How do you plan on adding the sear and hammer?

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Jonathan

Moderator

Yeah the trigger and hammer is where I've been spending all my time. I actually lost the original metal trigger group. Spent the last few days turning the place upside down with no luck. My only other option is to use a 1377 grip.
The hammer, just a piece of steel attached to a pin to cock it. Pretty simple. Rear cocker. I will get some pictures up once I get the mess cleaned up.

Alright well here it goes.
Spent some time tinkering and here is what I'm going with so far.
Here's a shot of all the parts for general scale.

https://drive.google.com/file/d/1kBZ7RM ... p=drivesdk

One thing you'll notice right away with the 140/1400 tube, is there Is about 3/8" extra room for a hammer to slide around in.
Here I decided to drill a set of holes at the very back end, same as you would see on a 1377 or 2289. This way I can capture the rear of my grip frame, and set the sear back that extra 3/8".

https://drive.google.com/file/d/1k-8Fey ... p=drivesdk

Here is my rear cocker hammer set up. I actually had it made by someone here on the forum, many moons ago anyway it looks a little unrefined in it's old age. It is well used. I repurposed it for this build. The hammer you see here used to be the cocking knob... But it all fits together this way.

https://drive.google.com/file/d/1jtD1w6 ... p=drivesdk

Here's a shot of the front end of the valve. Another oddity of the 140, the stud treads into the valve which in turn holds the stock. Simple enough right? Why didn't they put a shoulder on that stud to fit the hole in the tube properly? I took care of that. And the second step I cut into it captures the front of the grip frame as well. For the time being it works at least during mockup.
Take note, you can't just go and throw a 1377 valve into the 140 tube. The inlet is actually drilled off center to allow for the extra depth of the mounting stud. Well maybe you can drill out a 1377 valve but that's asking for trouble. Pretty sure I made that mistake somewhere along the path.

https://drive.google.com/file/d/1jprDME ... p=drivesdk

Now, my secret weapon. Maximum pump efficiency. Aside from using good seals and a nice flat top piston, you want to reduce pump head space as much as possible. The tiny air spaces between the piston face and the face of the check valve, may seem insignificant. At maximum pressure these spaces will eventually equalize in pressure to what is in your valve. At that point, the valve stops taking air and you're pumping for nothing.
Since I am not a machinist, I can't place the check valve directly against the piston head. In my mind that would be ideal. Correct me if I'm wrong. Instead what I do is install a tiny brass tubing sleeve into the inlet. Use epoxy or JB weld, solder if I'm using a brass valve. Being careful to not make a mess...
It works. Try it you'll like it.
Sorry for the pic quality.

https://drive.google.com/file/d/1jp2Z7Y ... p=drivesdk

Some issues that need addressing... The valve, since I'm using a 140 front half and a 1377 back half, the mounting stud and the exhaust port don't line up properly, requiring me to unscrew the valve a half turn. Can't see that working out as I'll pop the oring.
So I'm using the original exhaust port as another valve securing screw point. I'll drill a new exhaust port to my liking.

If you look at the 140 tube, in the pump linkage slot where the piston hits TDC there Is a little channel impressed into the inside of the tube... I'm guessing they thought it would keep out dirt or something. Anyway with a flat top piston, the oring sometimes likes to get sucked into that little channel and not aspire any air.
Now I haven't checked yet if it'll work, but I think if I remove some material from the pivot block at the front of the gun, it'll allow me to draw the piston back that extra inch. If I could somehow fill or smooth that channel out, I'll have an extra inch of usable pump stroke. In the past I have drilled a pin hole just so the piston can breathe.

Any insight is much appreciated.
Stay tuned for more.

none of those links work for pictures...need access to view

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"A candle loses nothing by lighting another candle"

Should work now. Settings were private.

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"A candle loses nothing by lighting another candle"

So, I had the gun put together to see if everything was working and I ran into a pretty good road block. The tube is rusted on the inside where the valve would seal. Looking down the tube from either end it's nice and shiny except for a little ring where the oring sits. It just looked like some residue build up so I ignored it basically. Anyway there you go.
Now I guess I have to order a piece of tubing and make a new one... Unless someone has an idea that might work. I was thinking maybe epoxy or JB weld to get a smooth surface? All I got at this point.

A piece of dowel with sandpaper. Cut a slit in the dowel and insert the sandpaper. Use a drill to hone the inside of the tube.

_________________
Jonathan

Moderator

I thought about trying that. My concern is that I might oversize the tube and it won't seal. It's pitted up pretty deep. I'll try it though and see.

It works! The valve is sealed somehow. I don't get it the rust has to be just behind the seal or something.
Anyway... It's really ugly.
Show off some half arse machining work here.
You can see the transfer port is brass tubing, ID of .161 all the way to the back of the pellet, using a flow through bolt that is a friction fit, kept the oring just in case. Pinned the barrel into the receiver with some set screws.

Double pinned the valve...

I didn't mess with the valve, no custom material addition or subtraction to adjust volume. Just filled the bleed off hole with a set screw, drilled the exhaust port and that's it.
Using the original 140 piston it seems to build pressure fast.
10 pumps even seems too much. I'm setup for total dump valve. No retention.
Enough ranting. Have to set up the chrony.

https://drive.google.com/file/d/1lTxw-W ... p=drivesdk

https://drive.google.com/file/d/1lSwO13 ... p=drivesdk

https://drive.google.com/file/d/1lOEDOq ... p=drivesdk

https://drive.google.com/file/d/1lGLzEl ... p=drivesdk

https://drive.google.com/file/d/1lMFk9r ... p=drivesdk

You have been warned. Not for the faint at heart.

https://drive.google.com/file/d/1lUKidC ... p=drivesdk

Looks good.......An older member that used to frequent this forum Doc Frankengun would of loved this creation.

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Jonathan

Moderator

I remember him, wasn't he a moderator at some point?