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Removal of K43 gas piston

befus

Active member
OK, got the shooter's kit and springs. All was well till I tried to switch out the gas piston. Solid a a rock. Have been applying Kroil every few hours to no avail. Any tricks, or advice. I got this rifle to shoot, but don't want to ruin it either.
 
Did you check YouTube?

Yes I did. Penetrating oil was the only suggestion, with the only variation being the brand. Thought someone here might have a magic formula. I just don't know how much pressure to apply, maybe I'm babying it?
 
Per the G43 expert dude Apfeltor, I used a torch to break one loose. It did the trick.
Eric
 
Mine came loose with Kroil applied for days and vibrations from me hammering out the front sight.
 
Use penetrating oil and let it sit a few days.

Then use a adjustable wrench on the gas block and a wrench on the piston like in the youtube video and it should unscrew.
 
I am a Kroil Oil believer. Let it soak for a few days. A little heat may be needed but never for me. Patience and care first IMO.
 
Still no luck. Adding a drop of Kroil two of three times a day and once a day I give it a crank with the wrenches, but nothing doing other than the crescent slipped and boogered the piston slightly......grrrrr. Keeping after it and will add a torch to the mix tonight.:facepalm:
 
Still no luck. Adding a drop of Kroil two of three times a day and once a day I give it a crank with the wrenches, but nothing doing other than the crescent slipped and boogered the piston slightly......grrrrr. Keeping after it and will add a torch to the mix tonight.:facepalm:

The crescent wrench is only for the gas block. The gas piston requires a fixed size beefy Craftsman wrench, not some adjustable junk.
I wonder if the rifle was previously owned by a member of the "but I always flush the barrel with hot water after shooting corrosive ammo" fan club. Because in the gas block, that's where the corrosive brine ends up and happily festers while sitting in the safe.
 
The crescent wrench is only for the gas block. The gas piston requires a fixed size beefy Craftsman wrench, not some adjustable junk.
I wonder if the rifle was previously owned by a member of the "but I always flush the barrel with hot water after shooting corrosive ammo" fan club. Because in the gas block, that's where the corrosive brine ends up and happily festers while sitting in the safe.

Well Mike I know the last time he shot it he didn't as the bore was still filthy ;) I cleaned it first, and thankfully it wasn't surplus ammo, as the bore cleaned up nicely with no pitting, or sign of corrosive ammo. The fellow I got it from said he had not shot it and included an unused shooter's kit, so there is no telling how long the piston has been in place, could even go back to the war. I doubt it, but after something like 10 days of Kroil applications, still no progress. I'm an old, and thus much more patient, man than I once was, so I'll just keep at the slow, but hopefully sure method.
 
Every step above noted. what size wrench are u using? A small one won't do it. Move a size up or two. Keep the action on the stock for more leverage and hold on with your legs. make sure you place well cover underneath the barrel.
 
Every step above noted. what size wrench are u using? A small one won't do it. Move a size up or two. Keep the action on the stock for more leverage and hold on with your legs. make sure you place well cover underneath the barrel.

IDK how you get a non-crescent "beefy" wrench? Best I can tell a 9mm is about right as a 3/8's is a tad loose and a 5/16's won't fit. None of them are much bigger than a carpenter's pencil. I'll go to Home Depot and see what options I have tomorrow. IF I leave the action in the stock it sure limits the use of a torch I found out today as the wood is going to get REAL hot in a hurry. I'd have to take out the action, heat it up, and quickly drop it in the stock, add tape to not mar the finish of the gas block and crank away with my new beefy wrench.....nothing's easy.
 
I removed a stuck gas piston by putting a cork in the muzzle and filling the bore with Kroil until the gas piston was overflowing.I let it set for several days muzzle down.I removed the action from the stock and held the top of the gas block in the padded jaws of a vise.The gas piston on mine did not fit a 9mm wrench.I didn't measure it but appeared to be around 8.5 mm.I used a 8 in crescent wrench to remove the piston.It was very tight.There was no corrosion or gummy lube on the threads.I assume the Germans had a special tool to remove the gas piston.
 
Almost everyone who owns several G/K43's has been through this problem, be patient. It may take a day or two for the Kroil to do it's job.
 
My penetrating oil of choice is a 50/50 mix of acetone and automatic transmission fluid. Best penetrant I've ever used! I keep a mixture handy in my garage and it best stores in a glass bottle.
 
IDK how you get a non-crescent "beefy" wrench? Best I can tell a 9mm is about right as a 3/8's is a tad loose and a 5/16's won't fit. None of them are much bigger than a carpenter's pencil. I'll go to Home Depot and see what options I have tomorrow. IF I leave the action in the stock it sure limits the use of a torch I found out today as the wood is going to get REAL hot in a hurry. I'd have to take out the action, heat it up, and quickly drop it in the stock, add tape to not mar the finish of the gas block and crank away with my new beefy wrench.....nothing's easy.

Don't not use a torch. Milwaukee makes an adjustable temp heat gun that I've used for these types of problems. Make sure you take the action OUT of the stock before you heat it up.
 
The wrench size that fits the best is a 3/16" British Standard which is the same as 1/8" Whitworth
 
If you have a long wrench you can get a little more torque. I used a hammer to tap the wrench. Mine came out with 15 minutes of effort, so I guess it was relatively easy.

t
 

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