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Hey gang

Broke down my M1A to check things over and I noticed that my piston is off center and canting to the left.

Now my op rod guide is inline with the gas cylinder…wonder what is causing it and is there a fix other than sanding down the back end of the piston?
456431

456432
 

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thehun06,
There shouldn't be any clearance between the op-rod and the piston, this can be detrimental to accuracy. With muzzle down if you have clearance between piston and op-rod you need a different piston. The gas system is designed to push the op-rod not to smack it. If the piston is new then you should check the op-rod to see if the end has been messed with, the face should be square with the tube.

John
 

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What John said above. A little off-center isn't a huge deal but the piston face and op rod face should be flush. The piston should be what stops the forward movement of the op rod.....not the bolt roller. Any chance you are using gas cylinder shims? If so, you may have too many which now has the piston too far forward and the op rod is being held back by the bolt roller. Ask me how I know about that.

I's say that misalignment can come from:
1. Op rod guide position (if it wasn't set straight before pinning, or never pinned or secured)
2. Op rod isn't straight (they are not as perfect as we would like to think)
3. barrel timing
 

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Then I would say if the rifle is new then either the piston or the op-rod is too short, if the rifle is used then someone trimmed the piston tail end. This has been done to my rifles to increase dwell on the gas system, however once metal is removed it's very difficult to put it back on, you'll need a new piston. Someone on here should be able to tell you new length of a piston. I believe it's 3.6xx but not sure.

John
 

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Difficult to tell from an image, but it looks like something is out of square, maybe your Op Rod. You need to check the end of the Op Rod tube to see if it is square and perpendicular to the tube centerline. A small machinist's square would be the best thing.

Danny

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Sorry to jump in on this late, but if you tilt the rifle down, does the piston lose contact with the operating rod? I had a rifle in my shop that had a short operating rod from Springfield. It was electricnic's rifle. Ended up installing a USGI operating rod and no more issue. First time I ever saw that happen. I thought I was going crazy. The operating rod was stopping on the bolt roller. Not good!

Tony.
 

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The OP indicates he has two shims installed, but I don't see them in the photo. Where did you place the shims?
Not having contact between the gas piston and op rod causes vertical stringing and premature bolt roller failure.
 

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Hey gang

Broke down my M1A to check things over and I noticed that my piston is off center and canting to the left.

Now my op rod guide is inline with the gas cylinder…wonder what is causing it and is there a fix other than sanding down the back end of the piston?
View attachment 456431
View attachment 456432
FWIW, I saw the same thing on my new Scout and after asking everyone on the interwebs, I concluded it’s fine. Something about geometry. But don’t take my word for it.


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