Crosman 140 Help please

Crosman 140 Help please

Joined: August 15th, 2008, 2:28 pm

April 17th, 2011, 6:26 pm #1

Hi All,i have just bought a crosman 140,i have resealed it and made sure everything is in the correct order,if i pump it up at normal rate it doesn,t get much pressure only doing around 450 fps,if i wait say 3 seconds between pumps it will produce 550 fps at 10 pumps,don't really want to get more than 550 fps as i am in the UK and we have a 12flb limit,i would just like to pump at the normal rate,any help appreciated,cheers Mark.
Last edited by maw3370 on April 17th, 2011, 6:32 pm, edited 1 time in total.
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Joined: June 25th, 2002, 1:34 pm

April 17th, 2011, 7:36 pm #2

like the piston may not be retracting far enough to let air into the tube. I can't imagine why though. It's possible that by waiting you are actually pumping slower, which could make a difference if faster pumping were blowing air past the valve o-ring? Condensation often forms at the valve o-ring and sometimes pitts the inside of the tube. HTH
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Joined: May 17th, 2004, 4:36 pm

April 17th, 2011, 8:04 pm #3

Hi All,i have just bought a crosman 140,i have resealed it and made sure everything is in the correct order,if i pump it up at normal rate it doesn,t get much pressure only doing around 450 fps,if i wait say 3 seconds between pumps it will produce 550 fps at 10 pumps,don't really want to get more than 550 fps as i am in the UK and we have a 12flb limit,i would just like to pump at the normal rate,any help appreciated,cheers Mark.
Once I installed the new pump cup and adjusted the linkage, the gun would suck air very slowly and had to be pumped slow, leaving the lever open for a second or two before closing. I suspect tolerances were off and the new cup barely let enough air in. You could try drilling a small hole just clear of the end of the pump cup when the arm is full extented. Make sure to de-burr it well. It won't hurt anything - you'll just suck air better. That gun should do 650 fps on 10 pumps. If you want that, get rid of the small stock transfer port and install 1/4" poly icemaker tubing. You'll need to countersink a 1/4" hold in the breech to accept the tubing but it's the single most effective mod for that gun. You'll be at 700 fps on 10 pumps with that.

"but I'll be needin' that gun, fer squirrels and such."
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Joined: April 1st, 2009, 3:18 am

April 18th, 2011, 3:39 pm #4

Hi All,i have just bought a crosman 140,i have resealed it and made sure everything is in the correct order,if i pump it up at normal rate it doesn,t get much pressure only doing around 450 fps,if i wait say 3 seconds between pumps it will produce 550 fps at 10 pumps,don't really want to get more than 550 fps as i am in the UK and we have a 12flb limit,i would just like to pump at the normal rate,any help appreciated,cheers Mark.
...the piston length... It has to suck air in and is very restricked in stock form. One modification some have done is to drill a weep hole in the tube to allow air in more quickly - works like a charm. Get it in the right place! You will notice that the tube has a stamping to allow air in. The newly placed hole needs to go just before the end of the stamping - towards the butt end of the rifle and then deburred with a rat tail file or the similar.

On one of the many I have owned, I completely did away with the old style pump cup. Instead, I had a 2100/2200 metal piston assembly cut in half (too long in stock form) then drilled and tapped, then cut threads in the piston rod. This made it compatible with modern, current Crosman pump cups. You can also have a flat-top piston made too that uses an o-ring. Cheaper replacement of the seal going that route; just an o-ring. The valve is a flat top valve in the gun, but I have not noticed any gains in power using a flat-top piston versus the Crosman cup.

Your rifle will produce a little over the UK limit with these simple attentions to detail.

Also, do the transfer port mod on your rifle. Do a search here, along the lines of, "140 transfer port mod", "1400 transfer port mod", etc.

"Well, I thought it was a rabbit but it turned out to be Bear Grylls in a rabbit hide."

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