From: none@none.com99   
      
   On 5/10/2025 3:24 PM, Snag wrote:   
   >    Today at the yard sale I picked up a Crosman "American Classic" model   
   > 1377 for ten bucks . It doesn't pump , and I think it's probably the cup   
   > on the pump . Part is available for a few bucks and I'm wondering if I   
   > should replace the rest of the seals and o-rings too . Is there anything   
   > in there that I wouldn't have in a box of assorted o-rings ? I've also   
   > seen "big bore" sleeves for the barrel/pump connection , looks like   
   > something an enterprising old fart with a machine shop could duplicate ...   
   >    BTW , this pistol has the rotating sleeve instead of a bolt , cocks   
   > by pulling on a knob on the back end of the pump sleeve . I have no idea   
   > how old it is but it doesn't look exactly like the current model .   
      
   I resealed a 1st generation Model 1 in .22 I think they use the same   
   plenum and knock valve.  My son might have his grandads 1377.  Hold on.   
   Let me go look in his gun safe.  I think they all have similar internals.   
      
   Would you have the seals?  Its been a while since I had my Model 1   
   apart.  I don't recall.  I seem to think there might have been something   
   different, but its not hard to take apart and look.  I think there are   
   even some videos on YouTube doing it.  Got a cup with a lid or a zip   
   lock bag to keep things in?  Take it apart and look.   
      
   Yes, you should replace the seals and o-rings.   
      
   The cup is probably bad, but probably so are the seals on the plenum and   
   knock valve.  Works just like a PCP except it has a tiny little air   
   reservoir.  A spring loaded "hammer" slams into a pin opening the air   
   valve and dumping air into the barrel.   
      
    >> I've also seen "big bore" sleeves for the barrel/pump connection ,   
    >> looks like something an enterprising old fart with a machine shop   
    >> could duplicate ...   
      
   I have not seen that, but you absolutely could.  Things have to have as   
   good of a finish as a hydraulic cylinder, but its possible.   
      
   The problem with a large volume pump is that I don't think you gain any   
   power after a certain point.  Instead the air valve closes again without   
   releasing all the air.  In fact you can potentially get less power if   
   you over pressure the plenum because its harder for the hammer to open   
   the valve.  That's kind of how an unregulated PCP works in fact.  By   
   taking advantage of that principle.  Anyway if you have the arm strength   
   to spare it might pump to optimum charge with fewer pumps.  Or maybe I   
   don't know what you are referring to.   
      
   You can get more power out of a multi pump pneumatic if you increase the   
   strength of the hammer spring and/or enlarge the plenum.  Then more   
   pumps or larger pump "might" be give more usable power as long as the   
   plenum will hold it.   
      
   I just looked.  The one my son got from his grandad is a 2100, but I   
   think they have almost the same guts.   
      
      
   --   
   Bob La Londe   
   CNC Molds N Stuff   
      
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