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Discussion Starter · #1 ·
Hello,

I picked up what I think is a steal of an older NM M1A. I knew it wasn't perfectly pristine, but still looks pretty good especially for the price!

Anyway, I have a little bit of surface rust. A little on the flash hider (none in the barrel that I can tell), a little on the under side of the outside of the barrel. What I'm most concerned with is this little bit on the face of the gas piston.



How worried do I need to be? What's the best way to get shipshape where I don't have to worry about function?

Thanks.
 

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Try cleaning it up, elbow grease and some good oil. Dry it up so it is perfectly dry, re-assemble and perform the tilt test. If it will not pass the tilt test, than just order a new piston. Pistons are not an expensive part.

Do a search on Tilt Test if you do not know what it is.

Sadlak, as well as others, offer high quality pistons.
 

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I had a little on one, I used a brass brush and WD-40 to remove the surface rust. Then I used a nylon brush with some rust inhibiting grease on it and scrubbed that into the surface. Finally I wiped it clean and dry and called it done. No further issues.

I usually rub the particular grease I have into all my parkerized parts due to it's water resistance. Once after rubbing down the receiver with grease some water was accidentally spilled on it. The water beaded off it like a fresh wax job, made sure to do it ever since.
 

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Discussion Starter · #4 ·
It passed the tilt test no problem before I broke it down and discovered the rust.
 

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Depends on how far deep the rust goes. You could possibly give it just a light, light polishing with some really fine grit abrasive. If you go too far, they are not that expensive to replace...
 

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0000 Steel Wool and gun oil mixed with a tad bit of elbow grease
 

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Then I used a nylon brush with some rust inhibiting grease on it and scrubbed that into the surface.

I usually rub the particular grease I have into all my parkerized parts due to it's water resistance. Once after rubbing down the receiver with grease some water was accidentally spilled on it. The water beaded off it like a fresh wax job, made sure to do it ever since.
Not trying to hijack but what grease names brother namesGI2
 

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I'd try some fine copper wool and Kroil anywhere you see rust. Copper's a good rust lifter and arrester. Kroil's a good penetrant.
 

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There are a lot of good suggestions, just use the one you like best and some common sense you will be fine . If you mess up it is a Cheap Replacement Part as Previously stated
 

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Not trying to hijack but what grease names brother namesGI2
I use XF-7. I don't "grease" the piston or cylinder. Just lightly apply the grease to the piston and tail and remove it with a soft clean cloth. I don't get any inside the piston and never inside the cylinder. The rifle ran flawless after doing this and the piston remained rust free.
 

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How about blasting and parkerizing it? These aren't stainless are they? Heat a coffee cup of park solution in the microwave, glass bead blast the piston, dunk it for 10 minutes.

An yes, some stainless will rust.
 

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The pistons are stainless, as is the gas cylinder. Considering that kind of effort I'd just buy a new piston... You'll probably need to polish the piston portion after blasting it too.
 

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How about blasting and parkerizing it? These aren't stainless are they? Heat a coffee cup of park solution in the microwave, glass bead blast the piston, dunk it for 10 minutes.

An yes, some stainless will rust.
Don't think I'd do that either. Notice the finely polished bands of the piston? They are that way so that they don't score the bore of the gas cylinder. Parkerizing would, if I'm correct, score the GC bore terribly.
 

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I'd bet a bunch o' beers that a parkerized piston wouldn't drop down into the cylinder.

If you did somehow manage to get it in there (hammer?) it wouldn't function very much.
 

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G.I. gas pistons were precision GROUND for a reason and were not polished after grinding. The advice to use any kind of brass, bronze or scotchbrite pads with bore cleaner or oil will not affect the surface and are a good idea. When it is clean and dry, I also put a very thin coat of Hoppe's Number 9 (standard formula) to keep it from rusting, but good oils would do the same or better.

I realize 0000 steel wool won't do much to the surface when used with oil, but I wouldn't use it there. I definitely would not use a polishing wheel with polishing compound on it.

A piston can have more rust pitting than one might think and still function/shoot well, but there is no reason to push the inherent design of the system.
 

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What about corrosion inside the gas cylinder? Is that ever an issue and if so what is the fix?

(I posed that question after getting up at 3:00AM to drive to work for an international conference call. After getting some coffee in me I realized GC corrosion may never be an issue, but will let the question stand because you guys never cease to amaze me by the wisdom that gets shared here. Maybe this is one of those "teachable moments".)
 
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