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PostPosted: Sat Oct 05, 2013 7:59 pm 

Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
It seems that Ace has a keen eye. I posted an answer to Plinkercases concerning the problem he had with his Walther lever action rifle and one of my reply had a picture of my O-ring kit. Beside the box, he noticed the piston and he sent me a PM to know the size of o-ring that would go on a Crosman 2289 piston.


He was very close, the piston on the picture was for a 1377 which is similar to the 2289.

So this question decided me to complete this post that I had been neglected for some time.

It started with my 1377 that was not building pressure anymore. I suspected that it was a problem related with the cup seal.

After removing it, I could’t find anything wrong with it. It seems to still be flexible and I couldn’t see any nicks on it.

Being a cheap miser who didn’t want to spend any more money than needed, I decided on a home-made fix.

I looked in my O-ring kit (from princess Auto) and found that a 7/16 x 5/8 might be the ticket.

I jammed it behind the cup seal and inserted it back in the the tube. When I pushed I could feel a resistance. Good news. On the return trip for the second stroke… bad news. The cup stayed stuck inside the tube because the thickness of the o-ring prevented the positive locking of the cup to the piston.


Now I had to dismantle everything.

What is the size of Allan key to remove the small breech screw???

Why I was thinking that it would be a metric size, I don’t have a clue, but after trying all I had (it was either too small or too big) I discovered that it is 50 thou. or .050 inch. Luckily I had a set that with the right key.


So to solve the problem, I had to make a groove to accommodate the o-ring behind the head of the cone seal, that way the cone seal bulge at the back could firmly locked in the end of the piston as it was intended to be. The result was that the o-ring was now captive in-between both.




I re-assembled the pistol and, bingo, it was working again.

I hope this cheap fix would be useful to some other peoples.

R-Gun Pete

PostPosted: Sun Oct 06, 2013 12:18 am 
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Joined: Mon Feb 11, 2013 12:46 am
Posts: 4389
Thanks for the post Pete and the return pm. :wink:
I messed up my 2289 piston on a mod i was doing. And H2P was cool enough to sent me one that he had siting in his parts bin thanks again H2P :wink:
But the cup seal rubber looks to have gotten hard or something and doesn't seal as it should. So i had the idea to stuff an o-ring as you did but the one i had was a little to thick and wouldn't fit when i tried to insert it in the tube. then i seen your reply to plinker's post and it couldn't of been better timing :)
I'll get the size you mentioned and give it a shot thanks.

"A candle loses nothing by lighting another candle"


PostPosted: Sun Oct 20, 2013 3:47 pm 

Joined: Mon Sep 03, 2007 7:56 pm
Posts: 174
Location: Sidney, BC.
You realize that those pump cups are easy & cheap to replace try Scopes & Ammo...KEN.

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