GTA
Airguns by Make and Model => Vintage Air Gun Gate => Topic started by: RBQChicken on March 28, 2018, 10:49:03 AM
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I finished resealing a 140 for a friend. At first I tried to get by with the original pump cup, but found it was a loose fit and wouldn't pump air, so I got a flattop piston head from Mac1 and installed it. Now, it pumps air, but it seems to "stick" in the tube every now and then. Usually it's near the top of the stroke when it sticks and you have to almost give it a little jerk to get it to move past the sticking point to finish the outward stroke. I've sometimes noticed it stick a little in other spots but not as much.
Is this normal until the o-ring wears in? That's all I can think of, is that o-ring, being a tighter fit, is sticking once in awhile.
Also, I'm getting only 545 fps on 8 pumps, and 580 on 10 pumps with 14.3 Crosman domes. Seems a little weak, or is that within spec for these guns. It's a Sears branded 140, fourth variant from 1962 or 1963.
It holds air overnight, so the valve seems to be in good working order. Thanks!
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I have no experience with that piston, but maybe it needs some lubrication? I'm also interested to hear if you discover what's causing that issue.
As for the velocities you're getting, check the graph on the first post of this thread:
https://www.gatewaytoairguns.org/GTA/index.php?topic=18193.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=18193.0)
rsterne reports getting ~680 and ~720 fps at 8 and 10 pumps, respectively.
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Thanks. I did see that article, but wanted to know if his gun was exceptional or if that's the norm for these guns.
I do have plenty of lube (ND 30 wt) on the ring and in the tube.
I'm starting to wonder if the pump tube could be slightly out of round in a couple spots.
As for the low perceived power, this gun doesn't seem all that hard to pump. I would have thought since the valve and pump tubes on these guns are smaller than the Sheridan's you'd have to have a lot harder pumping to approach the same power as a Sheridan.
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If the problem is that the tube isn't perfectly round and the o-ring doesn't break-in, maybe a different durometer or material will conform to the tube better. Just guessing.
As for the tube diameter and pumping effort, smaller diameter pump tubes take less effort to get to high pressure, but require more pumping to get the same volume of pressurized air. A high pressure shock pump, for instance, is easy to pump up to 300psi, although it takes many strokes. A much larger diameter floor pump takes quite a bit of effort to get to 100psi, and that's using both arms!
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That's interesting. If that's the case you have to wonder how rsterne could get velocities equivalent to Sheridan's with the same number of pumps (8 pumps got him into the upper 600's which is equivalent to a Sheridan that's shooting very well).
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I finished resealing a 140 for a friend. At first I tried to get by with the original pump cup, but found it was a loose fit and wouldn't pump air, so I got a flattop piston head from Mac1 and installed it. Now, it pumps air, but it seems to "stick" in the tube every now and then. Usually it's near the top of the stroke when it sticks and you have to almost give it a little jerk to get it to move past the sticking point to finish the outward stroke. I've sometimes noticed it stick a little in other spots but not as much.
Is this normal until the o-ring wears in? That's all I can think of, is that o-ring, being a tighter fit, is sticking once in awhile.
Also, I'm getting only 545 fps on 8 pumps, and 580 on 10 pumps with 14.3 Crosman domes. Seems a little weak, or is that within spec for these guns. It's a Sears branded 140, fourth variant from 1962 or 1963.
It holds air overnight, so the valve seems to be in good working order. Thanks!
I have a 140 that's similar to your configuration.
I replaced the stock piston head with a brass head and O-ring.
Otherwise the gun is stock.
I only changed the piston and I can feel air from the TP when fired
so it needs more work but that's what it gets now.
I think mid-high 600s is normal with 8 pumps.
Chrony results with CPHP 14.3:
08 pumps=654 FPS
10 pumps= 692 FPS
This gun gets:
08 Pumps=730 FPS
10 pumps=811 FPS
https://www.gatewaytoairguns.org/GTA/index.php?topic=133626.msg1330351#msg1330351 (https://www.gatewaytoairguns.org/GTA/index.php?topic=133626.msg1330351#msg1330351)
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Do you have rust inside your tube?
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sounds low power wise
is the piston adjusted up correctly and the probe o ring and tp gasket are they sealing ok
try swapping the piston o ring for a softer one I think Mac 1 supplies 90 grade milspec one's which I find too hard for piston heads
did the valve o ring get past the pivot pin holes ok without getting nicked
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The pump tube looks shiny. IIRC, I scrubbed it with mother's mag polish when I had it all apart (it's been awhile since I took it apart). I then cleaned all the polish out, of course.
The piston is adjusted to full length, and transfer port and bolt probe seals are good, no air loss.
I think the o-ring on the outside of the valve is okay. There were no burrs as far as I could tell for it to get caught on. The valve was a snug fit in the tube. The lower than normal pressure does make you wonder, though.
I think the easiest thing to try first is to replace that hard o-ring from Mac1 with a softer, black o-ring. If that doesn't work I'll probably have to tear the whole thing down and check the o-ring on the outside of the valve.
The fact that it holds air overnight tells me the seals inside the valve are okay.
Aside from the occasional tight spots when pumping, the pumping seems too easy. The force needed for pumps 6,7, 8 is not all that much more than on the earlier pumps. This is leading me to believe the problem is with the seal on the flattop piston. Then again, it could be that seal on the outside of the valve letting the air by, but that's harder to get at so I'll try the piston first.
I wonder if Lowe's or Menard's carries O-rings?
Thank you, gentlemen, for your thoughts. I will report back with my findings.
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The pump tube looks shiny. IIRC, I scrubbed it with mother's mag polish when I had it all apart (it's been awhile since I took it apart). I then cleaned all the polish out, of course.
The piston is adjusted to full length, and transfer port and bolt probe seals are good, no air loss.
I think the o-ring on the outside of the valve is okay. There were no burrs as far as I could tell for it to get caught on. The valve was a snug fit in the tube. The lower than normal pressure does make you wonder, though.
I think the easiest thing to try first is to replace that hard o-ring from Mac1 with a softer, black o-ring. If that doesn't work I'll probably have to tear the whole thing down and check the o-ring on the outside of the valve.
The fact that it holds air overnight tells me the seals inside the valve are okay.
Aside from the occasional tight spots when pumping, the pumping seems too easy. The force needed for pumps 6,7, 8 is not all that much more than on the earlier pumps. This is leading me to believe the problem is with the seal on the flattop piston. Then again, it could be that seal on the outside of the valve letting the air by, but that's harder to get at so I'll try the piston first.
I wonder if Lowe's or Menard's carries O-rings?
Thank you, gentlemen, for your thoughts. I will report back with my findings.
The 140 has a raised area at the top of the slot to allow air transfer.
When pumping make sure you open the pump arm all the way and pause.
You should hear a slight hiss as the vacuum is released.
If the pump linkage is worn it may not allow the piston to extend fully.
Also if the seal is too tight it may not allow the air to escape causing low power.
I always use 70 duro polyurethane o-rings in my vintage guns on the valve and piston.
http://www.theoringstore.com/index.php?main_page=product_info&cPath=367_454_455&products_id=16090 (http://www.theoringstore.com/index.php?main_page=product_info&cPath=367_454_455&products_id=16090)
You can drill a breather hole as seen here:
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OK don't yell at me....I'm a lowly vintage enthusiast. As such when it comes to resealing/restoring vintage guns I always go with the seals and parts the gun was designed for. I try to keep them as stock as possible. I have resealed many 140/1400's and never had an issue but then I put a pump cup back on it that it was engineered for. And yes Randy, your 140 should be shooting harder than 580 on 10 pumps. In my experience it should be closer to 650 fps or better with 14.3 gr. pellets. WOW "Tack Driver 10" near 700 fps is real hot!
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OK don't yell at me....I'm a lowly vintage enthusiast. As such when it comes to resealing/restoring vintage guns I always go with the seals and parts the gun was designed for. I try to keep them as stock as possible. I have resealed many 140/1400's and never had an issue but then I put a pump cup back on it that it was engineered for. And yes Randy, your 140 should be shooting harder than 580 on 10 pumps. In my experience it should be closer to 650 fps or better with 14.3 gr. pellets. WOW "Tack Driver 10" near 700 fps is real hot!
A healthy 140 with an O-ring piston, TP mod, and slightly increased ports will get about 720 FPS with 10 pumps.
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Okay, I took the gun completely apart again and really went to town making sure the pump tube was free of any rust or rough spots. Put a 20 gauge brass brush on a cleaning rod and stuck it in the drill and went back and forth several times, then followed up with a rag or two slathered with Mother's aluminum and mag polish, wrapped around cleaning rod for a snug fit and twirled it back and forth through the tube, also using the drill.
Followed with a few clean rags to clean everything out, then a couple of oily rags (ND 30 wt). I replaced the buna o-ring on the valve with a slightly tighter white o-ring (the extra one you get from Mac1 when you get the flattop piston), hoping to solve any leaks around the valve.
One other thing I noticed when I first put the gun back together was that the exhaust valve cap (the brass cap with the quad ring) seemed to be a little too tight sliding through the exhaust valve ring. It must not have been a problem because the gun fired well and re-cocked well so it wasn't too much friction for the hammer spring to overcome, but since I had the gun apart anyway, I polished the inside of the exhaust valve ring with the Mother's polish, then cleaned and slightly oiled the inside. Still had a snug fit but the valve cap slid a little easier through there so I accomplished what I wanted.
I replaced the white O-ring that came on the Mac1 flattop piston head with the Buna o-ring that I took off the valve.
When I got the gun all back together but before driving the roll pin in to hold the front end together I put a drill bit in place instead to check the pumping. It pumped very smoothly and after shooting a few times I thought I'd try the white O-ring again. Put that on and it was back to sticking in spots, as though the O-ring was a little too tight. Actually, they do seem to be a little tiny bit thicker than the Buna O-rings of the same diameter. I wanted the smoother pumping so I want back to the Buna o-ring.
When I got the gun all back together it pumped very smoothly and after shooting a few times I chronied it with 14.3 Crosman domes and was getting around 615 fps on 8 pumps. There's nice suction by the o-ring and you can here a good slurp of air at the end of each stroke. I figured this was as good as it was going to get and was happy with it. This was two days ago.
Today, I chronied it again and found it was shooting slower, just over 600 fps on 8 pumps. I thought if anything it would shoot a little better because in my experience with Sheridans they seem to shoot faster after having had some oil in them for a couple days.
I shot some more, thinking the speed would creep up a little, but no dice. I put a little more oil on the felt and on top of the piston head as well and pumped and shot a few times, then chronied it and now it was down to about 585 on 8 pumps!
This is the Sears version, so it has the white plastic spacer. I noticed a tiny bit of oil escaped in the area of the transfer port on both sides (just at the bottom of the white plastic spacer) so there isn't a perfect seal, but it's not too bad a leak because if you hold kleenex draped over that area there is no indication of air leaking when you fire the gun.
Can too much oil slow these things down, and if so, will it improve after cycling many “clearing” shots to blow the excess out?
Thanks.
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Yes you should pick up some speed after the excess oil gets run through. You might not be noticing the Kleenex moving when shot because of the extra oil? Did you change out the original TP port?
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The gun was originally missing the transfer port seal but had the metal top-hat shaped sleeve that the seal sits over. I ordered what I thought was the correct seal but it wasn't tall enough. Now that I think of it, I think I ordered the seal for a 130, not a 140. I don't know if all 140's have a plastic spacer between barrel and pump tube but this is a Sears variant and it has the white spacer. The tp seal I got didn't quite make it to the top of the top hat shaped sleeve. I cut a piece of ice-maker tubing to act as a spacer. Slid it over the top hat, then the 130 seal, and that brought it to the right height (it was just protruding a little above the concave surface of the white spacer. I figure it could be leaking a little through the gap between the seal and the spacer I made.
Anyway, I figured out what the problem with the power was. There is play in the pump arm linkage. It's a little worn around the rivet. When you pump the gun that play in the rivet hole takes up some of the overall length of the pump rod assembly and causes the loss in power. I know the best thing would be to replace the pump assembly but I'll check with the owner to see what he wants to do. I lengthened the pump rod and that brought the power back up to 615 or so. It's amazing how little an adjustment in rod length will significantly affect power on these guns.
The rifling is definitely the "ghost" type rifling, very faint. Turns out the gun isn't all that accurate, so that's another reason for holding off on replacing the lever/link assembly.