Garand Failure to Cycle/Piston too long

[alexanderkidd]

Have a very nice Garand that shoots great, but just can't get it to cycle 100%. I was shooting progressively hotter and hotter loads with 150 grain FMJs and 45-49 grains of H4895. Noticed cycling was improved with hotter loads but never 100%.

I inspected the gas system and discovered that the piston on the end of the op-rod seems to stick out too far. The piston tip extends over the gas port hole. I heard that this can happen if a Garand is re-barreled from an AGI Garand gunsmithing video.

Is there a way to fix this? I'm considering grinding down the piston or cutting coils off the stock recoil spring.

[HANDYMAN]

I don't think that is your problem. If you have a caliper measure the diameter of the piston itself. It should measure at least .525. If it's less than that you want to start there by having a new piston installed.

[country gent]

This can be an issue ocasionally, the old armorrors fix was to corectly locate the gas tube on the splines and mark with a sharp scribe, then lightly peen one side of the spine same side on all 3 spines ttighten it in place and locate it Another issue is an out of spec gas tube lock. It should go to 8:00 and then be backed up to 6 and locked with gas plug. Op rods are getting expensive and good ones are hard to find. Finding someone to weld the new piston on to your op rod is hard. The gas tube is expensive and getting hard to find good ones also. I would be hesitant to grind on the piston thinning the face of it. Clipping coils on the recoil spring can cause timing issues and other feeding functioning issues.

[alexanderkidd]

This can be an issue ocasionally, the old armorrors fix was to corectly locate the gas tube on the splines and mark with a sharp scribe, then lightly peen one side of the spine same side on all 3 spines ttighten it in place and locate it Another issue is an out of spec gas tube lock. It should go to 8:00 and then be backed up to 6 and locked with gas plug. Op rods are getting expensive and good ones are hard to find. Finding someone to weld the new piston on to your op rod is hard. The gas tube is expensive and getting hard to find good ones also. I would be hesitant to grind on the piston thinning the face of it. Clipping coils on the recoil spring can cause timing issues and other feeding functioning issues.

Would you also need to drill a new gas port in the barrel? It looks like if I moved the gas tube forward enough for the piston to rest at the correct spot, the hole does not appear in the top window of the gas tube.

[Char-Gar]

Before you do anything, buy a new recoil spring. Clean and lubricate the rifle and install the new spring. I will bet that cures your problem.

[country gent]

How much is it off? That window has quite abit of room around the hole

[DCM]

This is purely speculation as I cannot see this one, but did someone add a new end to the op-rod without shortening it up??
I havent seen them in a while but they used to be commonplace.

[bruce drake]

http://shuffsparkerizing.com/
I recommend Tim Shufflin's work. Good turn-around with quality work at a decent price. He specializes in WWII rebuilds and M1 Mini-Garand...

[rondog]

Wow, is it possible the gas cylinder is on one thread too far?

FWIW - I bought a cylinder kit from The Garand Guy, and my M1 shoots like a new one now!

[alexanderkidd]

Before you do anything, buy a new recoil spring. Clean and lubricate the rifle and install the new spring. I will bet that cures your problem.

Good advice, unfortunately that was the first thing I tried. It's got new springs and has been cleaned and lubed.

[alexanderkidd]

This is purely speculation as I cannot see this one, but did someone add a new end to the op-rod without shortening it up??
I havent seen them in a while but they used to be commonplace.

It's possible... how would you tell?

[alexanderkidd]

How much is it off? That window has quite abit of room around the hole

The window is as you described but the hole is set back enough to be covered when the gas tube is mounted forward enough that the piston tip is where it's supposed to be.

[DCM]

It's possible... how would you tell?

I just dug out my spare op-rod.
It measures 15 15/16" from the tip to the spring hole, 17 5/16" to the back of the flat squared off area behind the spring hole and 23 9/16" stem to stern.
The piston tip is about 9/32", 0.151"

[Gtek]

Years ago I purchased a pack of springs, all new. None worked, all too stiff with correct size material and length. I have had all the "stuff" to check everything for a long time. If the M1 is not functioning with correct ammo there is not a whole lot of parts responsible. Op-Rod, Gas cylinder, spring, and possibly a leaking gas plug. It is designed to function from lock set to almost one full turn back and not blocking port. Optimal is 6-8 o'clock bottom to back up, unless you have a box full you may not find perfect. Slide the cylinder off with rear assembled and see where it falls to port on barrel.

[smokeywolf]

When my dad did the redeisign and rebuild on this Garand 103451 he wound nearly 300 different operating rod springs before getting 2 or 3 perfect ones that would feed anything he loaded into it.

smokeywolf

[W.R.Buchanan]

If your gun is barely cycling with hotter and hotter loads then what is probably the problem is the piston has become worn and is now too small with relation to the gas cylinder.

In other words you are getting blow by. This is a very common problem.

The correct clearance between the ID of the cylinder and the Piston is .004 to .007, if it is more,,, the action will not cycle reliably. Mine was .008 and it wouldn't cycle at all.

The fact that your gun won't cycle reliably with 49 gr of H4895 probably means the piston is loose in the cylinder. The gun should and will cycle reliably with 45 gr of IMR 4895 which is virtually the same powder as you are using with longer individual grains. This is my standard load.

I had this same problem and made a new piston. This is not hard at all if you have a lathe. I made the piston head the same length as the original and then drilled out the tack weld in the operating rod and removed the old piston,,, inserted the new on and tacked it back in.

Problem solved.

The only hard part is getting an accurate measurement on the ID of the Gas cylinder and you will need to use a "Telescoping Gage" and micrometer to accomplish this. There is a possibility that your gas cylinder is worn as well, however making a larger piston will still cure the problem because you are making the piston with .004 clearance to whatever your gas tube is.

Gas cylinders are a lot more expensive than the little piston if you have to buy one. The fact that this part can be made from a piece of 1018 or in my case a piece of 12L14 means it costs virtually nothing. The new piston needs to be tacked onto the Op Rod with a rosette weld in the existing hole with a heliarc. That way you won't go Ape and pile on a big unsightly weld.

Even if you have to have this done for you it shouldn't cost more than $50,,, It just isn't that hard.

I was lucky to befriend the guy who rebuilt the 25,000 Garands that were imported and sold by Arlington Ordnance in the mid 90's. My gun had this same problem and he told me how to fix it. I set mine up at .004 clearance, to my worn Gas Cylinder. It runs strong.

This is a heck of a lot better than buying a bunch of parts you don't really need.

Hope this helps. :mrgreen:

Randy

[alexanderkidd]

Thanks everybody for the info. Looks like the gas piston is undersized and will need replacement. I'll be looking into finding someone qualified to replace it.

[lonewelder]

The cmp now rebuilds op rods and will even trade yours out for a rebuilt one.also I think columbus machine rebuilds them too.

[W.R.Buchanan]

Alex: When you decide who is going to do the work for you, make sure to send you gas cylinder along with it.

It is pointless to replace the piston with a stock sized piston if the cylinder is worn. As I said in post #16 if the cylinder is worn too big an oversized piston will save the day.

If there is no oversized piston available then one can be made by anyone with a lathe and a piece of cold rolled steel. It is about the simplest part you can make.

Good luck and let us know how it turns out.

Randy

[seagiant]

Hi,
All you guys owning ANY of Mr. Garands firearms should get this book just to understand what you are shooting! HIGHLY recommended!

http://www.amazon.com/U-S-Caliber-Operated-Service-Rifles/dp/B0006F5XOW

[W.R.Buchanan]

I have several of Jerry Kuhnhausen's shop manuals. Every one has everything there is to know about the given subject.

Good thing to have if you are going to shoot something very much.

People need to realize that guns are machines, and they wear and have idiosyncrasies just like any other machine.

Learning about each gun is a task unto itself and should be regarded as part of the fun, and it will make you a better shooter as well since running the gun is part of shooting and if you don't understand how the gun works then running it becomes more difficult.

This starts with reading and studying accurate materials about the subject. Kuhnhausen's books are accurate material.

Randy