GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: Rivers3Plinker on October 29, 2014, 04:20:27 PM
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Guys,
I've been using the AC Customs flat top piston and valve setup all year. I've had to replace the o-ring in the piston several times on both of my guns due to wear from insufficient oiling. I have noticed with regular oiling they last longer and the gun makes more power just by simply oiling it every time before use, but I don't always do it. I've also found black oil inside the valves which is from the o-ring rubbing off the bluing and the o-ring, buna-n material itself.
Bart mentioned using Dremel felt polishing wheels as a felt oiling ring behind the piston head. This probably works fine using the 1/2 inch felt wheels from Dremel and expanding the center hole to fit on the 1/4-20 threaded shaft of the piston. This would also I think expand the OD of the felt wheel to that of the pump tube and make it fit perfectly but I have not tried it.
Instead I ordered some 1/4 thick 3/4 OD x 1/4 center hole felt washers from McMasters along with some other stuff. To fit this, I mocked up the washer on the threaded section behind the piston and used a sharpie to mark the area proud of piston head. They are 3/4 and you cannot squish them down to fit inside the much smaller pump tube. I tried.
After realizing they wouldn't fit, I took a scissors and cut off the marked area as best I could.
After butchering off this material with a scissors, it was no longer nice and round after that, but...it was still a little oversized and packed into the pump tube soaked in oil, it deformed into shape and size just perfectly.
I am amazed at the results!
I highly recommend doing something like this if you run any flat top setup without an oiling ring.
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i just add a few drops of secret sauce every tin/500ish shots . FWIU too much oiling will build up in the valve and cause problems . i got my AC F/T setup last year and i'm on the second o-ring . when i put in the 3rd/last one AC supplies in i'm gonna order a some viton o-rings to replace all four of them .
http://www.gatewaytoairguns.org/GTA/library/Standard%20O-Ring%20Composite.htm (http://www.gatewaytoairguns.org/GTA/library/Standard%20O-Ring%20Composite.htm)
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i just add a few drops of secret sauce every tin/500ish shots . FWIU too much oiling will build up in the valve and cause problems . i got my AC F/T setup last year and i'm on the second o-ring . when i put in the 3rd/last one AC supplies in i'm gonna order a some viton o-rings to replace all four of them .
http://www.gatewaytoairguns.org/GTA/library/Standard%20O-Ring%20Composite.htm (http://www.gatewaytoairguns.org/GTA/library/Standard%20O-Ring%20Composite.htm)
Viton...any particular reason to use this material over say Polyurethane?
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"Excellent temperature and chemical resistance.
Excellent mechanical and physical properties.
Low compression set and low gas permeability.
Not for use with Acetone, Skydrol, or ethyl Acetate.
Basic temperature range: -20 F to +400 F*"
better temp. and chemical resistance along with higher temp and mechanical (friction) resistance from all the pumping .
each material has it's fans so this is just just my opinion ....... and we all know what those are like . LOL .
heres the o-ring sizes if you don't know what they are . .
http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,1288.0/topicseen.html (http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,1288.0/topicseen.html)
WyoMan knows these guns inside and out and he prefers the softer 70D rings for pumpers .
it's splitting hairs IMO ..... but the price of o-rings is so cheap going overboard is only pennies difference per o-ring so why not ?
here's a good source for 0=rings .
http://www.mcmaster.com/#o-rings/=udpwoh (http://www.mcmaster.com/#o-rings/=udpwoh)
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I feel every piston should have a felt wiper to help prevent over oiling. most of that drop of oil gets wiped to the front of the valve with the first stroke and the thing is way over oiled for that time and then starved as more pumps go by.
if you have a wiper it leaves a thin residue over a lot of pumps and keeps things even. In my opinion it does not matter whether flat top or cup or material it should have a wiper...
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"Excellent temperature and chemical resistance.
Excellent mechanical and physical properties.
Low compression set and low gas permeability.
Not for use with Acetone, Skydrol, or ethyl Acetate.
Basic temperature range: -20 F to +400 F*"
better temp. and chemical resistance along with higher temp and mechanical (friction) resistance from all the pumping .
each material has it's fans so this is just just my opinion ....... and we all know what those are like . LOL .
heres the o-ring sizes if you don't know what they are . .
http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,1288.0/topicseen.html (http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,1288.0/topicseen.html)
WyoMan knows these guns inside and out and he prefers the softer 70D rings for pumpers .
it's splitting hairs IMO ..... but the price of o-rings is so cheap going overboard is only pennies difference per o-ring so why not ?
here's a good source for 0=rings .
http://www.mcmaster.com/#o-rings/=udpwoh (http://www.mcmaster.com/#o-rings/=udpwoh)
Yep - WyoMan posts on CAPOF for building pumpers have helped me a great deal with my mods.
My first thought was the buna-n are wearing down, so find a material with better wear resistance.
I bought from Mcmaster as well and went with 70d polyurethane so we'll see how that goes. Maybe they won't last or work out well but I was looking at the abrasion and tearing resistance properties primarily since that's what was happening with the Buna-N. Mcmaster has a chart showing o-ring material properties and I followed that. I just noticed PU is not highly rated for resistance to hydraulic fluid, although that's not exactly what we're putting in the pump tube. Animal vegetable oils rated good though. Maybe I should try some canola oil!
(http://images2.mcmaster.com/Contents/gfx/small/j05-oringsd1-gis.png?ver=13533646)
In the end, if using an oil wiper that should make a huge difference in that aspect (wear) regardless of material or durometer. So if the polyurethane doesn't hold up, I can switch back to 70D buna-n which were cheap, and I have a big bag of them from Mcmaster as well.
FWIW I have tried the 90D on the piston too. What I found was without oiling it every shooting session, pumping action was sticky and jerky. It could actually get that way after 20 or so shots. I suspect with a 90D o-ring and an oil wiper, it would work pretty well but still maybe not be a smooth as the 70D. But I have a bag of 90D Buna-n from mcmaster too so I can play.
In a few months if I have any findings one way or the other, I will post.
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I have a triple o ringed brass flat top piston Gil Irvin made me years ago.
Long story short, I added a felt wiper and I'm using Mil Spec 90D Urethane o rings...I packed the space between the wiper and last head o ring with divers silicon.
It self lubes, doesn't migrate into the valve and pumps *butter smooth*.
Just a thought for your mods......
Mike