Pump Arm Question

dockie · February 09, 2013, 10:14:48 PM

I built myself a wooden pump arm grip for my 1377 and it worked great for a while, but lately the linkage seems sloppy and it wont stay in the Up position after I take a shot. I'm sure you guys can tell me whats going on right? Thanks in advance.

WyoMan · February 09, 2013, 10:29:27 PM

Can only guess that the piston does not have enough "cam over lock" on TDC to hold the extra weight of the wood.....
If you have an OEM piston you can stuff it and that should help if thats the problem....

edit: make sure front grip frme screw is tight because that helps secure the valve against the piston...hth

Crosshairs · February 09, 2013, 10:31:12 PM

Only thing i can think of is the weight of the wood, keep a few pumps in it should hold it up. Do you have a adjustable piston it could need a adjustment.

Mike

breakfastchef · February 10, 2013, 02:04:37 AM

Wyo and Crosshairs are on the right track. Shim and pin the pump cup if you are using the standard 1377 innards. If the piston is adjustable, it needs adjusting. Are you a 50 pump type guy? If the gun is used hard, especially with lots and lots of pumps, your valve may need to be pinned. An outside possibility is the pump pivot hole is getting elongated. This certainly could be a cause of your problem.

quickster47 † · February 10, 2013, 03:29:19 AM

Again what all the other guys say is spot on. But, is this a new gun or a well used gun. If it's new everything should still be tight but if it is a well used gun you could have a lot of slop and things need tightening up.

Carl

dockie · February 10, 2013, 10:58:57 PM

Thanks for the responses guys. Unfortunately I'm not sure what some of your advice means. Cam over-lock? Shim and pin the pump cup? Stuff the piston? I hate to sound like the newb that I am, but can you elaborate? The piston is original, and I haven't had the problem until recently.

This is what it looks like

1377x · February 11, 2013, 12:04:43 AM

looks good!
pin/shim the pump cup there is a topic about it here
put a washer under the cup run a pin through it throught the piston and the bottom of the cup

WyoMan · February 11, 2013, 02:01:46 AM

Quote from: dockie on February 10, 2013, 10:58:57 PM
Thanks for the responses guys. Unfortunately I'm not sure what some of your advice means. Cam over-lock? Shim and pin the pump cup? Stuff the piston? I hate to sound like the newb that I am, but can you elaborate? The piston is original, and I haven't had the problem until recently. This is what it looks like

No problem dockie...we sometimes forget that we have a second language here and need an AG dictionary

cam over lock is what holds the pump arm closed - your piston should contact the valve about 1/2" to 3/4" before the pump arm is closed
the best way to check is right after its fired, the pump arm should meet some resistance (contacting valve) before closed in the range above
If it doesn't (did you check that your hardware was tight - first do that) then here's a link that explains stuffing, shimming:
http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,9664.0.html

and here's one for valve pinning:
http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,10015.0.html

I linked to the ones I did because they easy to find but there is much much more here...
as Charlie Mellon would say thats how I learned

dockie · February 11, 2013, 02:30:53 AM

Thanks, this is great!

WyoMan · February 11, 2013, 03:47:35 AM

Very welcome dockie let us know how it turns out...
BTW, that is a nice looking 1377 but I don't think the cat is so sure....

Tater · February 11, 2013, 05:28:17 PM

Quote from: WyoMan on February 11, 2013, 02:01:46 AM
No problem dockie...we sometimes forget that we have a second language here and need an AG dictionary
cam over lock is what holds the pump arm closed - your piston should contact the valve about 1/2" to 3/4" before the pump arm is closed
the best way to check is right after its fired, the pump arm should meet some resistance (contacting valve) before closed in the range above
If it doesn't (did you check that your hardware was tight - first do that) then here's a link that explains stuffing, shimming:
http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,9664.0.html

and here's one for valve pinning:
http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,10015.0.html

I linked to the ones I did because they easy to find but there is much much more here...
as Charlie Mellon would say thats how I learned

I have a question for you. I have never opened up my 1377 to get to the piston/hammer before but I noticed my pump arm does not stay closed very well, it just barely holds. What hardware specifically should I check for tightness?

WyoMan · February 11, 2013, 05:36:46 PM

Hi Tater, the front grip frame screw also secures the valve and is hard to tighten with the trigger guard in the way.....
If this screw is loose the piston can shove the valve back and the lock will not be tight. I check these screws alot....hth

breakfastchef · February 11, 2013, 05:37:42 PM

Quote from: Tater on February 11, 2013, 05:28:17 PM
I have a question for you. I have never opened up my 1377 to get to the piston/hammer before but I noticed my pump arm does not stay closed very well, it just barely holds. What hardware specifically should I check for tightness?

There are no adjustable parts to correct that problem. If the pistol is still covered under the Crosman warranty, send it to an authorized Crosman repair facility. Otherwise, you are going to have to take it apart and make some minor changes to fix it.

Tater · February 11, 2013, 05:51:58 PM

Quote from: WyoMan on February 11, 2013, 05:36:46 PM
Hi Tater, the front grip frame screw also secures the valve and is hard to tighten with the trigger guard in the way.....
If this screw is loose the piston can shove the valve back and the lock will not be tight. I check these screws alot....hth

Thanks. That is the screw that takes a square-headed driver correct? (not sure the name of that type)

WyoMan · February 11, 2013, 06:43:40 PM

Do you mean slotted

I believe they're called combination...
there have been some new posts here about swaping them with thumb screw I believe
http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,9424.210.html
hope link works
and some folks use the hex drive with allen wrench

Chef made a good point about lack of adjustment..... if the pumper is pushed for power it will move something...
http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,9976.0.html

Lots of great stuff here and do what chef said if under warranty......hth