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  #1  
Old 12-15-2010, 09:42 AM
XDNine XDNine is offline
 
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Default #2 Pencil Carbine Gas Piston

While cleaning my NPM, I discovered that the Gas Piston is shaved or beveled on one side. Picture the eraser on a #2 pencil after you have used the eraser in the same spot for 10 minutes.

To my eye it was manufactured that way intentionally and does not seem to be a defect or some type of damage.

Two questions; will this hurt performance? So far it has worked great. And does it say anything about the manufacturer since the gas piston is un-marked?

I checked my Riesch book and could not find any reference to a gas piston being in this condition.

Any thoughts?
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  #2  
Old 12-15-2010, 09:06 PM
musketjon musketjon is offline
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I've seen lots of pistons but never one that looks like you describe. You know what they say about it not being broken. If it was mine, I would change it out for one that is in better shape. If you can't locate a piston, PM me and I'll send you one.
Jon
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  #3  
Old 12-15-2010, 10:35 PM
Firstflabn Firstflabn is offline
 
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Kuhnhausen shows .009"-0.14" clearance between the o.d. of the piston shaft and the i.d. of the piston nut. A little over the thickness of a piece of copy paper on each side. The piston shaft should be .299"-.300". The max gap between the piston head and the cylinder wall is an incrediblly small .0015". The gas has to get past the head before it could sneak by the piston shaft.

If the rifle cycles reliably even with slow ammo it means the gas channel is reasonably clean and if you keep everything well lubed, you're good as is.
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  #4  
Old 12-16-2010, 01:59 AM
musketjon musketjon is offline
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[.009"-0.14" ]

I think you mean .009-.014.
Jon
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  #5  
Old 12-16-2010, 03:08 PM
Pitt323 Pitt323 is offline
 
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A couple of thoughts . . .

- The majority of gas pistons were/are unmarked.
- The piston should move in and out easily, without binding.
- They are hardened steel. I have never seen a deformed one . . .
- Replacing a piston is a snap IF the piston nut is not staked. You may want to get the proper tool, though.
- Pistons and nuts are readily available from Numrich, CTD and many of the other reputable firms and web sites.
- Look at the slide where the piston contacts it. If there is no deformation or burring, you should be O.K. Usually, this contact point looks like a round polished spot.
- If the piston is badly deformed ( pointed or shaped like a chisel) it could damage the slide.

Since you state that the carbine functions fine (functions reliably and does not leave excess powder fouling around the nut) I would just keep an eye on things.
If the piston nut is not staked and/or you are able to remove it without damaging the threads I would swap out that piston just for peace of mind.
Let us know what you decide, and good luck.
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  #6  
Old 12-16-2010, 10:06 PM
Firstflabn Firstflabn is offline
 
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Right you are, jon. Thanks for straightening me out. Not much ooomph if the clearance was 0.14". Wonder what Bubba was trying to accomplish with the trim job?

Really doesn't matter as long as there is one place along the piston shaft with the full section. Can't tell for sure from the description.
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  #7  
Old 12-17-2010, 03:19 PM
musketjon musketjon is offline
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Not to brag but I actually have a piston marked PI. Only one I''ve ever seen marked.
Jon
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  #8  
Old 12-17-2010, 04:21 PM
XDNine XDNine is offline
 
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Thanks for the feedback guys. And thanks musketjon for the offer of a (PI marked) replacement gas piston too. (Kidding)

So I need a special tool to remove the gas piston nut right?
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  #9  
Old 12-17-2010, 06:55 PM
musketjon musketjon is offline
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[So I need a special tool to remove the gas piston nut right?]

Correct you are, Sir. It's called (amazingly) carbine piston nut wrench. They're not very expen$ive and can be found at gun shows.
Jon
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  #10  
Old 12-17-2010, 09:38 PM
Pitt323 Pitt323 is offline
 
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Lightbulb

Quote:
Originally Posted by XDNine View Post
Thanks for the feedback guys. And thanks musketjon for the offer of a (PI marked) replacement gas piston too. (Kidding)

So I need a special tool to remove the gas piston nut right?
You'll do a lot less damage to the nut (and cylinder) if you use the proper tool.
I got mine from GunBroker - Garrison Mfg. - $15 plus shipping.
Later I saw some on CTD for $9.95. I think Numrich has them, too.
Check out the various web sites and get the best deal you can.

P.S. If the nut is staked, even the tool won't help you much. I have some that just won't bust loose, staking or not . . .
But it's worth a shot . . .
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