Nitro Piston Replacement Benjamin Trail AW NP .22 950fps

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Offline roti83

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Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« on: April 10, 2013, 06:14:51 PM »
Hi - first time on forum and am impressed with content.  My new Trail has 520 rounds fired before failure i.e. Piston fires but will not push pellet out of loading position down the barrel.  My understanding is that this is not a common occurrence and this model has been somewhat reliable.  I am going to replace the nitro piston so am looking for a reference on the forum that I could view.  I have sourced a piston.  I am happy with the rifle as at times I was able to shoot dime size five shot groups @ 10 meters when I found the right pellets.  The symptoms that I experienced on the way to failure were inconsistent shooting, vertical stringing 6", reduced deformation of fired pellets and finally failure.  On checking cocking force on a scale it registered 20 lbs. substantially below the  approx. 30 lbs.  The only mod done to the rifle is the addition of a Charlie Tuna trigger which in my experience is highly recommended and not difficult to do.  When replacing the piston I am looking for references not only for disassembly/assembly but simple tune up measure that I can do including recommendations on lubrication on assembly, polishing (to de-burr) the ram (not the inside of the cylinder) etc. any references would be appreciated.  Thanks. 

Offline OleTomCat

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #1 on: April 10, 2013, 06:25:45 PM »
Check out the GTA Libraryhttp://www.gatewaytoairguns.org/GTA/index.php?action=library.

In there you will find link to documents on tuning your gun and sights that have the documents and manuals you will need.

Along with a few helpful hints and tips...
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Offline Doug Wall

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #2 on: April 11, 2013, 08:06:02 AM »
Are you sure that it's the piston? Sounds more like the piston seal is blown. That's a lot cheaper than the NP. If it still cocks, and fires with authority, but no pellet movement, then it's the seal. One thing to check- Make sure that you don't have multiple pellets stuck in the barrel!
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Offline BmaS

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #3 on: April 11, 2013, 09:47:55 PM »
Welcome to the GTA!

The vertical stringing is indicative of seal failure.  Beware, you may find multiple problems. 
You will need a spring compressor, and a few basic tools. You will want a brake hone, a selection of 320 grit and 400 grit sand paper, a few dowel rods, some files and honing stones, a non-petroleum de-greaser such as Simple Green and/or citrus Goo-Gone, molybdenum paste grease, Super Lube grease, a 12 gauge shotgun bore mop, and some 30 wt pure silicone oil, an adjustable wrench, common and phillips screw drivers, and a small curved pick.  You will also need your replacement parts.  At the very least, I would have a replacement seal onhand.  Other "must-have" upgrades include pivot bushings and GRS from Airguntoys and Charlie's GRT-III trigger.

Remove the action from the stock, and the barrel block from compression tube.  Place the compression tube in the spring compressor, and remove the rear plug pin and trigger block screw.  Ease the tension off the compressor, and remove the rear plug.  Pull the gas ram out of the compression tube.  Remove the trigger block.  Pull the main piston out of the tube.

Remove the compression tube from the spring compressor, and clean thoroughly to remove the gunk and Chinese mystery oils.  Hone the tube with the brake hone, cross-hatching as you go.  De-burr the sharp edges of the cocking slot and the cocking shoe, and the slot where the trigger block lives.

Clean and polish the inside and outside of the main piston, paying attention to the ends.  De-burr any sharp edges.  If you have the GRS, install it on the gas ram.

Check the seal of the main piston for damage.  Replace if necessary. 

Prepare the compression tube by swabbing a pea-size amount of Super Lube grease on the inner walls using the shotgun bore mop.  Apply a small amount of Moly paste to the main piston, remaining vigilant to not allow Moly in front of the seal (it is okay to lube the sides of the seal with Moly).

Reverse the tear-down process to re-assemble.  Install brass pivot washers in barrel block and lube with moly before re-installing barrel block into forks of the compression tube.

Entire process takes anywhere from 3 to 6 hours.

Crosman Titan GP .22 -- GRTIII "Gateway drug"
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Offline roti83

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #4 on: April 12, 2013, 12:44:23 AM »
Thanks - all great information.  If it turns out to be the seal then I will have a spare gas ram.  Once I am done I will post the results.  Thanks again.  Great forum!!

Offline tilbertscott

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #5 on: April 14, 2013, 01:17:39 AM »
I wish I had people like sam b. To work on my break barrel it would be neet to see two minds think alike kind of thing
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Offline BmaS

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #6 on: April 15, 2013, 01:51:29 AM »
I wish I had people like sam b. To work on my break barrel it would be neet to see two minds think alike kind of thing

I'm glad share whatever knowledge I have about airguns.  Most of it I have gained from others on this site.  I've opened and tuned more than one rifle, but I am no pro.  Don't hesitate to ask, I'll answer what I can.  I also have no shortage of opinions; if you don't have one of your own, I'll give you mine ;D ;D ;D
Crosman Titan GP .22 -- GRTIII "Gateway drug"
Reminton NPSS .22 -- CBR   "Clang"
Diana 34 T06 .22 (x2) -- TWINS!
Beeman R1 .22 -- "Mein Fraulein"
HW30S .22 -- "Mädchen"
CCS 2400KT .22 --  "Baby"
Disco .22 w/ BNM -- "Easy"
Custom 2240 -- Hers
Custom 2250 carbine -- Hers
Custom 2240 -- mine
Crosman 1077 "CO2 sucker" -- Hers
Tanfoglio Witness 1911 CO2 BB -- Hers
Daisy 880(x2)
Daisy 822 -- Arkansas can opener
Daisy 1200 pistol
Daisy 188 pistol

Offline roti83

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #7 on: April 19, 2013, 12:58:34 AM »
Sam - why do you polish the inside of the piston? 

Well I have pulled the gun apart, seal seems to be ok but noticed that there was oil in and around the trigger end of the compression tube and in the back spring guide.  No, I did not oil the rifle except one drop in the compression chamber (Crossman silicone oil) after it failed to see if it would help.  Not sure the source of the oil unless it came from the gas spring.  I found a honer so will hone the cylinder and deburr etc.  Thanks again for all the comments.

Offline BmaS

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #8 on: April 19, 2013, 08:44:08 AM »
There can be (and usually are) burrs inside the cavity of the piston that will cut into the body of the gas ram. It will cause horrible scraping noises, scrub the paint off the ram, and it can affect the shot cycle.  It doesn't take much.  Wrap some emery cloth around a dowel rod, insert into the cavity of the piston, and twist. 400 grit "wet or dry" sand paper works well.  You can split the end of the dowel rod, or use tape to secure one end of the paper and wrap it around.  It should be a snug fit.  You will have to adjust the amount of sand paper until you get it right. Wipe it down good to remove sanding debris, and apply a little (emphasis on little -- spread thin, light coat) moly to the body of the gas ram.  It will all go back together smoothly.
Crosman Titan GP .22 -- GRTIII "Gateway drug"
Reminton NPSS .22 -- CBR   "Clang"
Diana 34 T06 .22 (x2) -- TWINS!
Beeman R1 .22 -- "Mein Fraulein"
HW30S .22 -- "Mädchen"
CCS 2400KT .22 --  "Baby"
Disco .22 w/ BNM -- "Easy"
Custom 2240 -- Hers
Custom 2250 carbine -- Hers
Custom 2240 -- mine
Crosman 1077 "CO2 sucker" -- Hers
Tanfoglio Witness 1911 CO2 BB -- Hers
Daisy 880(x2)
Daisy 822 -- Arkansas can opener
Daisy 1200 pistol
Daisy 188 pistol

Offline tilbertscott

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #9 on: April 19, 2013, 02:17:14 PM »
Instead of molly I chose locktight brand C5-A copper based anti-seize lubricant rated to 1800º F I looked it up and its what they put on the glock slides at the factory would you disagree with using this I've been using it I was thinking of cleaning my trail today cuz its nasty outside it seems reasonable and I've taken its guts apart after using it and seemed to hold up like it should its slippery but not too intense. I don't really use silicone on the seal cuz my gun is just too crazy after using even a drop I use it for my barrel pivit washers that are brass
  • Wadsworth, Ohio

Offline OleTomCat

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #10 on: April 19, 2013, 02:20:59 PM »
Scotty,

I don't use anything that combusts in my guns or guns that I work on for others so I would say no....

Than again I don't use Moly either so I may not be a good one to talk to....
  • Summerville, SC
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Sheridan Blue Streak, aka The Blue Demon Rebuilt Steroid Style By Mac1.
Gamo Silent Cat, tuned by Me, smooth as butter.
Crosman Storm, GRT-III trigger. Crosman N2 Ram. (For Sale)
Gamo Big Cat, GRT-IV Trigger, Custom installed N-Forcer Ram

Offline tilbertscott

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #11 on: April 19, 2013, 02:25:10 PM »
Kinda why I'm tearing it down today :/ thanks anyway for your info tomcat but what do you use?
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Offline OleTomCat

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #12 on: April 19, 2013, 02:28:23 PM »
Krytox is the cryogenic industries name for a ptfe based lube that is used for Oxygen Clean(~100% O2) systems and will not burn, though at about 600f it will off gas some nasty stuff, but if used correctly it will never see that kind of temp....
  • Summerville, SC
Home Of Air Guns Inc.
Air Gun Tuning and Targets

Air Guns:
Sheridan Blue Streak, aka The Blue Demon Rebuilt Steroid Style By Mac1.
Gamo Silent Cat, tuned by Me, smooth as butter.
Crosman Storm, GRT-III trigger. Crosman N2 Ram. (For Sale)
Gamo Big Cat, GRT-IV Trigger, Custom installed N-Forcer Ram

Offline tilbertscott

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #13 on: April 19, 2013, 02:33:42 PM »
Agreed i would imagine that the inside of the compression tube is possible to reach 600 but I was kind of just sharing my success with it gor the moment any of that lube ain't cheap and I had a ton of this
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Offline OleTomCat

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #14 on: April 19, 2013, 02:50:29 PM »
You can get the good stuff off of ebay for about $20.00 for enough to do two or three guns, or if you shop around like I did and found a knockoff that is a litle cheaper and buy a bulk amount you can get it for less...
  • Summerville, SC
Home Of Air Guns Inc.
Air Gun Tuning and Targets

Air Guns:
Sheridan Blue Streak, aka The Blue Demon Rebuilt Steroid Style By Mac1.
Gamo Silent Cat, tuned by Me, smooth as butter.
Crosman Storm, GRT-III trigger. Crosman N2 Ram. (For Sale)
Gamo Big Cat, GRT-IV Trigger, Custom installed N-Forcer Ram

Offline roti83

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #15 on: May 26, 2013, 01:43:16 AM »
Well I completed the strip down and re-assembly and everything works great.  Thanks to all the help and comments.  FYI - The problem was the gas ram which read 70 lbs on the bathroom scale when compressed.  The new ram started to dent the scale before I stopped trying to compress it.  The seal was fine, however, I replaced it and did the tune up of the receiver, compression tube etc. as provided in the write ups from the GTA Library.  i used a large wood clamp to remove the ram as suggested by another member's post and it worked great.  The relief distance to fully unload/load the ram was only about 3/8 in. when removing and replacing the ram in the receiver.  One minor point I found puzzling was in the lubing of the seal.  In one part of the write ups it suggested using moly paste on the piston but to be careful not to get the paste on the seal.  In the lube guideline it said moly could be used on the seal outer surface (sealing surface). Regardless I am now shooting and when I do my part it is 5 shots inside a dime at 30 ft. so onward and upward.  Great Forum - Great Help.  Thanks All

Offline OleTomCat

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #16 on: May 26, 2013, 03:41:14 AM »
Glad it worked out for you...
  • Summerville, SC
Home Of Air Guns Inc.
Air Gun Tuning and Targets

Air Guns:
Sheridan Blue Streak, aka The Blue Demon Rebuilt Steroid Style By Mac1.
Gamo Silent Cat, tuned by Me, smooth as butter.
Crosman Storm, GRT-III trigger. Crosman N2 Ram. (For Sale)
Gamo Big Cat, GRT-IV Trigger, Custom installed N-Forcer Ram

Offline The Guide

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #17 on: May 26, 2013, 05:31:29 AM »
All great info.  Thanks for sharing!

Jay
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Offline GKU

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #18 on: May 26, 2013, 05:40:02 AM »
Basic how to rebuild and how to get in there video :

https://www.youtube.com/watch?v=FeQQ6S6WgHc
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Offline benj397

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Re: Nitro Piston Replacement Benjamin Trail AW NP .22 950fps
« Reply #19 on: June 22, 2013, 09:12:05 PM »
Welcome to the GTA!

The vertical stringing is indicative of seal failure.  Beware, you may find multiple problems. 
.... You will want a brake hone, ....

....Hone the tube with the brake hone, cross-hatching as you go. 

Are all brake hones the same? i.e. grit and diameter?
How does one cross-hatch?

Can this cleanup be done with emory cloth instead?

Thanks
  • Memphis, TN

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