Crosman 1400 weird air leak

[Volvoguy]

Got a weird one here. I reasealed this rifle a couple days ago and have put a lot of shots through it. I have a 140 as well so I have had fun comparing the two. The 1400 has more crack to it but after putting a flat piston in the 140, they're both pretty similar.

What isn't similar is the issue. Both rifles have been those kinds of projects you take apart over and over. The 1400 leaks through the barrel but only when you're halfway between pump 5 and 6, then is hisses loudly. If I quickly pump, it usually stops by pump 7 or 8. Last shot I did I was able to nail an old spray paint can from around 40 yards at 11 pumps. I was shooting it and the 140 at 10, but added a pump for potential loss.

The rifle doesn't always do this though, so it's odd. I replaced the seals with a kit from eBay since originally it held no pressure at all. The surfaces seemed fine though the part the quad goes into has some damage on the retaining ring. I forgot the retainer was a thing, and was stuck a flat blade screwdriver across it and left an indentation when messing with the old seal. Anyways I cleaned that up well I had thought, but figured it may be worth mentioning.

Any help would be great!

[Volvoguy]

Alsoo, would anyoone know the size of the quad ring and where to order them in bulk? I measured mine and have close matches but I want to make sure.

[threesuns]

When I resealed my 1rst variant 760, someone suggest an O-ring, to replace the quad seal. I don’t know if they would be the same size as for a 140/1400. Maybe some else can confirm.

[Goose]

I have an older 760 that does something similar.  Sometimes it will whine after a shot, too.  I suppose video of that would be interesting.

I do believe that the o-ring is the same size.  4x8x2 mm.  Greasing it is recommended.

Cheers,

J~

[Ronno6]

Maybe here?

https://www.mcmaster.com/products/o-rings/cross-section-shape~x/

[Volvoguy]

Thanks eveyone. I didn't know you could replace it with an o-ring so I may try that if the problem continues. It's just a very odd problem. I did find a place that seems to have the proper quad seal in bulk as well, though I wonder why mine failed. If the problem is the brass housing and retaining ring, then putting in another seal won't do any good.

It held perfect pressure for 24 hours, though this time when pumped it did not hiss at me, so maybe I need to let it sit when it starts leaking after pump 5.

Another thing it started doing is blowing the bolt open when fired. Twice I had the bolt lift and open which suprised me. I may need a thicker o-ring to keep it in place. The o-ring I used on my 140 bolt failed to seal so I don't know how well this kit does with matching.

[Volvoguy]

When I resealed my 1rst variant 760, someone suggest an O-ring, to replace the quad seal. I don’t know if they would be the same size as for a 140/1400. Maybe some else can confirm.

Do you know why they reccomended an O-ring instead of the original quad? This rifle has a pretty tall quad seal so I wonder if it'll work. In my assorted o-ring kit I don't see anything that will obviousally work but I will have to try it sometime.

I have a leaking rifle (can't recall the model but it is a newer pump), so I can also try it on that one as well.

[Blowpipe Sam]

Baker airguns and Mac1 will sell you multiples of the quad ring.  Just ask them for some.
I suggest some moly paste on the trigger and sear components. The smooth function of the sear and the trigger is important for proper sealing of the valve cap. I’d check the nipple on the valve for nicks or dings but that’s unlikely.

Can you hear or feel the valve cap physically setback and seat against the sear on the first or second pump?  Some guns make an audible click.

It sounds like you might be pumping too fast?
Because of the pump design 1400’s make the most power when pumped slowly.  When you extend the pump arm you should hear a momentary hiss as the somewhat restricted intake port admits air past the piston.  I always pause and count “1 Mississippi” at the top of every stroke to make sure the pump chamber completely fills.  You should hear/feel the valve cap setback at the end of the pump stroke.  Resistance should start building after the third pump and the last two should be pretty hard to stuff in there.
If you don’t hear that hiss when you open the pump it’s time for some oil.

Hope some of this helps.

Oh yeah.  The blowing the bolt open thing is a problem.  A new O’ring helps but best to get in the habit of making sure the bolt is flipped all the way down before shooting.  I prefer the 140 style breech cover on my first model.  It’s much more secure.

[Volvoguy]

Baker airguns and Mac1 will sell you multiples of the quad ring.  Just ask them for some.
I suggest some moly paste on the trigger and sear components. The smooth function of the sear and the trigger is important for proper sealing of the valve cap. I’d check the nipple on the valve for nicks or dings but that’s unlikely.

Can you hear or feel the valve cap physically setback and seat against the sear on the first or second pump?  Some guns make an audible click.

It sounds like you might be pumping too fast?
Because of the pump design 1400’s make the most power when pumped slowly.  When you extend the pump arm you should hear a momentary hiss as the somewhat restricted intake port admits air past the piston.  I always pause and count “1 Mississippi” at the top of every stroke to make sure the pump chamber completely fills.  You should hear/feel the valve cap setback at the end of the pump stroke.  Resistance should start building after the third pump and the last two should be pretty hard to stuff in there.
If you don’t hear that hiss when you open the pump it’s time for some oil.

Hope some of this helps.

Oh yeah.  The blowing the bolt open thing is a problem.  A new O’ring helps but best to get in the habit of making sure the bolt is flipped all the way down before shooting.  I prefer the 140 style breech cover on my first model.  It’s much more secure.

I have the gun taken somewhat apart at the moment. I remoced the barrel and sometimes with one pump it will cock, but usually on the second pump it will click and I can see the components move. I will lube the tripper components up more and see what it does. If that doesn't get it then I guess I will have to take it 100% apart again which I have gotten a little tired of doing. Both the 140 and this 1400 have had to be apart several times.

The 140 sure does have a better breach. I replaced the O ring on my 1400 again and it has gotten a little better, but not as good as it should be.

[Glasstomb]

When I resealed my 1rst variant 760, someone suggest an O-ring, to replace the quad seal. I don’t know if they would be the same size as for a 140/1400. Maybe some else can confirm.

From Mac1:
An O-ring will work in the Cap for a while but the proper seal is a Quad seal.

I've used these: https://www.theoringstore.com/store/index.php?main_page=product_info&cPath=367_2205_111_115&products_id=5042

[bob27831]

VG,
I agree you need the right quad seal.  Also, check to make sure inside your valve chamber where the little white check valve plug goes is spotless.  If you get crud embedded in the nylon plug, it can foil the seal on the check valve and randomly leak or stick open.  Scrub out the valve with some twisted 4-0 steel wool and clean, clean, clean.  Inspect and replace the white plug if necessary.  I think the spring is about 1.25 inches and may be weak?  When you pump the 140/1400, any crud in the pump tube, has no where to go except the little intake hole on the flathead of the valve, thus getting mashed in the white check valve, so clean out that pump cylinder tube really well too before installing the pump rod.
tip:  until I have a 140/1400 running smoothly, I used a cut off nail the same diameter as the pump linkage roll pin, and slide a small o-ring over the end.  Lots easier to repeat a disassembly without having to pound out that roll pin repeatedly!
Hope that helps.

[chuckinohio]

 You can polish the seat for the white check valve by using a standard pencil eraser to dislodge any crust or flakes of funk. Simply stick it down in there and give it the old twist action.
  Polish the pin that transits through by the piece held by the breech screw and holds the valve cap closed against the valve.
  Polish the angled rear surface of the hammer that engages the sear, and the cylindrical portion as well. VERY CAREFULLY inspect your trigger sear for any obvious rough spots and address if comfortable doing so.
  I do not lube the hammer and associated parts that hold and seal the valve cap with anything but pellgun oil/ secret sauce/ ATF etc...

  This may free up the parts and allow your valve cap to seat on the first pump with a click like intended.

[Tack Driver 10]

These are what I use in the Crosman blow off valves.

https://www.mcmaster.com/90025K127/

They also have them in Viton 75 duro.
https://www.mcmaster.com/6540K118/

[JPSAXNC]

When you put the gun together The thick round disk with the hole in it that the breech screw goes into the screw hole is not symmetrical in the disk, the disk has to face a certain way. Your quad seal is probably fine, I just use an o-ring. A problem area for leaks in these guns is the inside of the tube where the valve o-ring contacts the tube, moisture builds up there, and can pitt the inside of the tube causing various amounts of leakage depending on the amount of pitting.