M1 Carbine gas piston


May 5, 2003, 09:55 PM
Hi Guys,

I just got a new IAI M1 carbine and I'm having trouble already. It seems accurate for a carbine but I had several stovepipes with various 15 round GI mags. I think the problem is that my piston is stuck. I would like to remove it with a piston nut wrench but it is staked in place.

Does anyone know how to remove the staked nut with the propper wrench? Is it just a matter of using enough force to overcome the staking? Any tips?


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May 5, 2003, 09:59 PM
Is it stovepiping the spent casing or the new round?

Check the extractor and it's tension before checking the gas system. Some IAIs had improperly tuned extractors.

Occam's Razor and all that. :D

May 5, 2003, 11:04 PM
If the piston was stuck all the time, you'd have a manually operated rifle....nothing would work unless you cycled it by hand.

Dribble some Hoppes #9 on the piston and bushing and leave it on there....hopefully it'll clean itself.

Ditto on checking the extractor. Don't try to take it apart without the little $15.00 GI maintenance tool, or everything will BOING all over the house.

May 5, 2003, 11:59 PM
Thanks Guys,

P&R: The stovepiping is with the empty cases and the ejection seems sluggish with the empties coming almost straight back at me over my right shoulder and not going too far.

DDA: I was told that the piston sould be freely movable and it's not in my carbine.

Anyone know if I can I remove the staked piston nut with the correct wrench and a little bit of force?

Art Eatman
May 6, 2003, 08:28 AM
A bit more "non-destructive" experimentation: First, try Liquid Wrench. After it soaks a bit, tap lightly on the piston to see if it frees up. Then fire a round to get it back to the rearmost position. Repeat the Liquid Wrench and tapping...

If no joy, seek expert advice. :)


PS: I'm gonna move this to the Gunsmithing forum.

May 6, 2003, 01:28 PM
It's usually not a good idea to put anything into or on the piston assembly. The super heated gas coming into the gas cylinder will carbonize anything, turning it into a sticky, tar-like mess.
These systems are meant to be "run" dry of lube, solvent, or any other liquid.

Many people don't know this, and either lubricate the gas piston, or inadvertently allow solvent or lube to leak into the gas assembly during cleaning. This is why it's a good idea to clean the Carbine with the action upside down, so nothing gets down the gas port.

To disassemble the system:
Buy the GI-type gas piston nut tool.
Field strip the action, and lock the flats on the barrel into a WELL padded vise. BE CAREFUL not to damage the rails the op rod "box" run in. These can be dented or damaged ruining the barrel.

Use the piston nut wrench to unscrew the gas piston nut. The nut will "iron out" the staked area.

Once the nut is off, remove the piston, using a block of wood to tap the gas cylinder if necessary to get it out. DO NOT attempt to grab the piston with pliers or other tools. If it won't lift or tap out, soak with a good penetrating fluid over night.

Once the Assembly is apart, soak and scrub the nut and piston with solvent and a brass brush. NEVER scrape the piston with any steel tool. If the piston is scratched, it will foul worse, and is ruined.

A good item to clean the piston with is a "Lead-Away" cloth that removes carbon.

Clean the inside of the gas cylinder and it's threads with a brass brush, and use a brass or copper wire to VERY gently clean the gas port into the barrel.

Once everything is clean, DRY everything well, put a TINY amount of lube on the nut threads ONLY, drop the piston in and thread the nut on BY HAND, until tight.

Tighten the nut snuggly with the nut wrench, then re-stake into one of the open slots.
Unless necessary, don't try to re-stake into a used slot, use a new one.

If either the nut or piston looks scratched or damaged, replace the part. They're cheaper than a new barrel.

Badger Arms
May 6, 2003, 04:29 PM
I'd use the above advice but caution you to use a synthetic lube. Synthetics don't turn black and gum up as easily. I'd also say you should clean your gun inverted so no more bore solvent gets into the gas cylinder. That's a caution I take with all of my autoloaders. Make sure the port is on top of the barrel while you clean. I even leave my cleaned gun on the vice overnight to make sure. Can't hurt.

May 9, 2003, 07:41 AM
I'm not trying to steal plinker's post, but I have a problem with the M-1 also. Mine is one of the DCM issues in '64 or '65 and was a new Underwood. To function properly, the top rear of the lug on the Operating Rod slams with some force into the bottom edge of the receiver. I don't like metal slamming against metal. It just isn't good engineering. There should be something to dampen the shock. Sooner or later something is going to give. I have tried increasing the tension on the OR spring, downloading, super-gluing a small piece of teflon on the slamming surface, and nothing works. If there is enough load to function the gun, it slams. I realize the gun was built for a specific purpose and was for all intents and purposes a throw-away, but I would like to shoot it more ( it IS fun) but I don't want to take a chance on damaging it because the rascals are approaching $500.00 now and mine is in excellent condition and I have loads of milsurp accessories for it. I asked DOPE BAG (excellent name for that bunch) and they blew smoke at me. I am considering having the OR slamming surface drilled in a couple of places and installing 2 STIFF buffer springs. Any ideas, guys ? ?

AZ Jeff
May 9, 2003, 12:41 PM
Winwun--althought the slamming of the op rod into the front of the receiver would seem to inherently be a "bad thing", the fact is that a carbine does not suffer from this.

The op rod and receiver of a carbine are pretty durable, and all that banging seems to have no effect.

Now, on the other hand, the true achilles heel of the little carbine is it's BOLT. Sooner or later, EVERY CARBINE will break it's bolt, it's just a matter of time.

For more on this, see Jerry Kuhnhausen's book on the M1 Carbine.

Badger Arms
May 9, 2003, 07:05 PM
A quick search of ebay yielded two guys who are selling gas piston nut wrenches. For those who want to know, Ebay, Gunbroker, and Auctionarms are almost always selling these things.

Ebay Search (http://search.ebay.com/search/search.dll?MfcISAPICommand=GetResult&SortProperty=MetaEndSort&ht=1&query=carbine+piston+wrench)


May 9, 2003, 07:55 PM
AZ, thanks for the feedback. I would say you are correct on all counts.

I have thought about beveling the lugs on the bolt so it could cam its way out of the lug recesses and would be a blow-back instead of gas operated. I see no need for the bolt to be locked in battery.

I religiously clean the piston and cylinder after each firing and use transmission fluid for lube as it doesn't gum and burn. I also run a 1/16" bit through the port to keep it wide open. My friends who are constantly experiencing broken bolts say they never clean the piston and cylinder.

I also use the M-2 bolt, the heavier round one, to assimilate as much of the kinetics during the cycle.

I have never had a broken bolt. I'm either lucky or am doing something right. I'd guess lucky.

May 12, 2003, 08:26 PM
Thanks for all the helpful hints, guys.

After soaking the piston in solvent, it's managed to loosen up a bit. I can wiggle it side to side and in and out about 2mm. Does anyone know what the propper length of travel for the piston should be. I'm sure it must be more than 2mm.

Thanks again.

May 16, 2003, 08:33 AM
I believe we were told in the military that the piston gave the OR the impetus to travel the 5/8" necessary to rotate the bolt lugs from their recesses. It is blowback the rest of the way. I always take mine out and clean it good and put it back, lubed with transmission fluid.

May 22, 2003, 07:17 PM
I have taken in an M1 carbine that is jamming about once in 8 shots. It's the stovepipe jam. I replaced every spring in the gun and now have done the gas port cleaning per your instructions.

I took it to the range today and started firing with a clip full. The first few empties ejected and flew out real good. The 8th empty jammed again. After watching the first 3-4, I thought I had it licked.

I noticed that the gas port itself has a very small counter ID just before it breaks into the barrel. Is this right?

Also after cleaning the nut, I noticed a very small spiral turn mark in the ID. Would this have an affect?

Got any ideas??

Thanks, Bill P

May 22, 2003, 07:46 PM
I have noticed significantly different strengths on the OR springs available for the little M-1. The one that was original on my 1943 Underwood was probably 66% of the tension of the "New" replacement I bought at a gunshow to reduce the "slamming" I was and still am having problems with.

Willp, it sounds like you have too much tension on the OR spring, or something is binding the rearward travel of the OR causing the bolt to not travel rearward enough to allow the empty to eject. I suppose you have tested the ejector spring to see if it has enough tension. Slowly extracting a round by hand, the ejector should give it a nice 8-10 foot flip as the round clears the chamber rims.

You don't need me to tell you how frustrating it is to have a problem that seems impossible to solve.

Good Luck.

May 22, 2003, 09:44 PM
It's possible the mark on the ID of the piston nut is collecting fouling and jamming the piston. It doesn't take much, which is why care must be taken not to scratch these parts.

I'd suggest picking up a brand new genuine GI piston and nut.

Drop the piston in the port and screw the nut down finger tight. See if the piston moves in and out freely. If it does, tighten down tight with the nut wrench and check again.

I don't think the carbine had a counter-bored gas port. If yours does, it's possible somebody attempted to drill the port out.

If you have no luck, you have two choices: Buy Jerry Kuhnhausen's M1 Carbine gunsmithing book, or find a Carbine-qualified 'smith.

At least Kuhnhausen's book will allow you to insure the parts you are working with are GI-spec, and will likely allow you to find and fix the problem.

These things were made nearly 60 years ago, who knows how many user/owners there have been, and God only knows what they might have done to it.

My only other advice is to get a bolt disassembly tool and strip the bolt down. Clean, check or replace the extractor and ejector assemblies. The problem might be as simple as a worn extractor, or as serious as a damaged chamber.

The usual causes of stove-piping are fouled gas assembly, dirty/damaged chamber, weak ejector spring, worn/broken extractor or spring, or a binding op rod.
Unless it's something really off the wall, it's probably one of those.

Don't get frustrated and give up.

Buy the book, and let us know what you find.

May 22, 2003, 09:54 PM
I've gone through the springs and ejector. All springs are new in the gun.
After I cleaned the gas plug and nut and replaced them, the plug moved freely.
There appears to be about .005 clearance between the plug and the nut so the plug wiggles back and forth just a little...Is this about right?

Dry-cycling slowly will throw a round out about 18 inches.

May 23, 2003, 01:40 PM
If the plug is only moving in and out of the cylinder .005", you've got a problem. There should be around 1/4"?? free movement.

It's sounding like you've got one of those rare off-the-wall problems that are hard to diagnose.

Get a small mirror and take a good look at the chamber for corrosion, roughness, rings, or other damage.

Take the action out of the stock, remove the recoil spring and guide, (leaving everything else in place), and check for free movement of the bolt/op rod. If you tip the barrel up and down, the action should slide open and shut on it's own weight.

Then try it in the stock, without the spring.

Buy a NEW, GENUINE USGI piston and nut. The old parts could have a problem not descernable to the eye.

Buy Kuhnhausen's book, or find a carbine-qualified 'smith.

( As a matter of interest: did you try another magazine or a different brand/type of ammo?) often these problems are ammo related.

May 23, 2003, 04:20 PM
The plug does move in and out about 1/4" freely. The .005 movement is the side to side.
The mag is a fairly new one and the ammo is American Eagle 110gr FMJ.

My next move is to buy a new piston and nut.

May 23, 2003, 11:09 PM
Just for the hell of it, try a different brand of ammo, you never can tell.

In any case, let us know how you come out.

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