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1377C modified piston cup

October 29 2009 at 10:44 AM
  (Login icarus402001)
Crosman Forum Member
from IP address 96.245.74.2

 
As you all know, SEARCH is useless. I remember seeing a pictorial and write-up
on modifying the piston cup to fit more closely to the valve. Not a flat face, but still conical. I'll be damned if I can locate it again. Can anyone direct me?

 
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(Login pneuguy)
Crosman Forum Member
70.144.181.198

Is this what you're thinking of?

October 29 2009, 10:50 AM 


 
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(Login icarus402001)
Crosman Forum Member
96.245.74.2

Re: Is this what you're thinking of?

October 29 2009, 10:55 AM 

That's the most recent reference I've seen. Thanks. I assume I'd need the adjustable piston and have to machine the cone on the valve to fit the cup properly.

 
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(Login pneuguy)
Crosman Forum Member
70.144.181.198

As you can see, James P. did that work. Hopefully he'll...

October 29 2009, 11:11 AM 

...see this thread and comment.

Steve

 
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(Login jct842)
Crosman Forum Member
216.134.239.168

search works fine with firefox

October 29 2009, 12:22 PM 

Search for Sort by Match Date
Question on 1377c Conversion View Thread on Feb 5, 2007 8:13 AM
and piston cup 760-140 as well. Dave
Help..1377c ...oil sponge??? View Thread on Jun 2, 2006 1:04 PM
is a plastic cup piston that pulls of the piston rod. Is my gun missing this oil sponge or dont the new 1377c
Can a 1377c be converted from multi-pump to CO2? View Thread on Jun 6, 2006 10:32 AM
The idea is to swap parts from another Crosman, then modify the piston to fit against the back
I often wondered about that piston cup View Thread on Feb 3, 2009 4:37 PM
It surely seems to be cupped far more than a seal need to be. Then too, some modify the fit
I have a 1322 with a rubber-cup piston and valve, with the latter... View Thread on Feb 3, 2009 8:26 PM
...custom modified (by James Perotti) to optimize the fit. The resulting pumping efficiency
Yes, a cupped piston and valve combo is good View Thread on Feb 5, 2009 5:41 PM
and the cupped geometry on the seal. Crossman does this for good reason. The gap between the valve
Yes it's slightly modified. View Thread on Jan 21, 2007 9:34 PM
It's got a aluminum piston with stock rubber cup, an angle exhaust port, and a reshaped valve stem
stock/modified 2289 velocities ? View Thread on Jan 23, 2007 11:08 PM
/barrel and converted the 1377 to .22 Modifications include: aluminum piston with rubber pump cup, lighter
Flat Top Piston Question text from Yellow View Thread on Jan 6, 2008 4:07 PM
, unless the piston is pulled back past the linkage slot. On the 1377C I am working on, if I make my piston
chrony results for modified 1322 -10" barrel with hobbies. View Thread on Sep 28, 2006 5:33 PM
OK mine has the steel adjustable piston and stock crosman cup seal.RWS hobbies are lighter 11.9gr
1 2 3 Next >>

 
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(Login icarus402001)
Crosman Forum Member
67.62.57.108

Re: search works fine with firefox

October 30 2009, 4:03 AM 

I still haven't seen what i remember reading on this forum last year. Maybe it was deleted during all of the upheaval over the summer. Damn shame.

 
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Donnie Fulwood
(Login DMF23)
Crosman Forum Member
74.182.73.28

Re: Is this what you're thinking of?

October 29 2009, 5:13 PM 

I made an adjustable cup type piston for my 1377 from a model 2100 metal piston inspired by an article entitled "Crosman 13xx HotRod Tech" I found here on the forum in the tech section or somewhere.

I cut.040" off the tip of the valve cone on a lathe to get a better fit between the cup and cone. Mine works pretty good but I just toasted the cup after about 12-1500 shots. Shooting 7.9 grain CP's it was doing about 770 fps at 25 pumps with a modded valve and transfer port when it died but I think it'll do better with a new cup. When I get my new cups in I'll let you know what the Chrony says.

 
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Keith
(Login icarus402001)
Crosman Forum Member
67.62.57.108

Re: Is this what you're thinking of?

October 30 2009, 3:55 AM 

Which mods to the valve? How does it do on 10 pumps?

 
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Donnie Fulwood
(Login DMF23)
Crosman Forum Member
74.182.73.28

10 pumps

November 2 2009, 8:11 AM 

Lighter valve spring, shortened intake valve (to increase valve volume), reshaped exhaust valve and stem (to increase flow), and 115 degree angled and enlarged exhaust port (to increase flow). Do a search and you'll find the valve mods here on the forum. And the poly tube transfer port mod as well.

With 7.9 grain pellets, I get 623fps on 10 pumps which is about 70fps more than it got stock before I modded the valve, transfer port, and added the adjustable piston.


    
This message has been edited by DMF23 from IP address 74.182.73.28 on Nov 2, 2009 8:17 AM


 
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