Is it the piston, or the tube that surrounds the piston. I know my tube is loose, but I have never heard it rattle.

 

it's it the piston or the gas tube? Some play in the gas tube is normal.

 

When I hold the operating rod/piston and shake it, there is a distinct rattling sound as if something inside has come loose.

 

Hmm, check with Terra, I recall her mentioning weights in the oprod awhile back.

 

There are weights inside the piston.
The rattle is normal.
Some have unscrewed the piston from the op rod and lost the tiny weights inside.
There are some posts about it somewhere.

 

Patient to Doctor: "Doctor, It REALLY hurts, but only when I do THIS!"

Doctor to Patient: "Well, stop doing THAT" ;D

 

Sounds like you are talking about the weights inside the piston moving back and forth. This is normal, per numerous posts here as well as my own experience.

 

There's not really anything that can come loose. The piston head is loctited with 242 and torqued on at 250 in lbs. The gas tube itself may be a little loose - there is a male notch on the gas block, which aligns with a female notch in the gas tube. If you put your barrel in without having the notches aligned right, you can ding up the corners on the female notch, which will allow a little more play in the tube. It will never be able to fully rotate, but the wiggling will increase some.

 

The piston head is loctited with 242 and torqued on at 250 in lbs.

The problem is loose weights inside the oprod/piston itself. It's been mentioned that some have removed the piston head to clear the weights and I have no problem doing that. I just wonder if removing the weights doesn't unbalance the piston. Apparently the gun operates fine without the weights though.

After removing the weights, is torquing the piston head back on to the oprod important or can I just eyeball it?

 

torquing on is recommended.

 

I would imagine the weights are in there to prevent bolt bounce.

 

Correct. You may also experience light strikes as well.

 

What would be recommended as far as re-attaching the weights?

 

I don't understand the question.. You mean how to reinstall them after removal?

 

Why in the world would anyone WANT to remove the weights in the piston/op-rod??? The XCR operating system was carefully designed to function flawlessly WITH them. I am sure there are some problems the design team decided the weights would cure, and you as the operator may not even be aware of ALL the possible problems that may ensue. If I tilt some of my AR's up and down I hear the same rattle. Guess what, it's the sound of the tungsten weights rattling in the H2 buffer. Same concept.

Why F--- with success :duh:

MadDog

 

Personally I wouldn't just go arbitrarily removing weights from the piston without having a complete understanding of the implications.

 

Well, the weights aren't "attached" to anything. They're just loose in there.

One thing you could do is remove the piston and stuff a tiny bit of cotton or something to take up the extra space. Might make a difference, and it wouldn't hurt anything.

 

Now there's a good idea. Thanks Terra!

 

here's a drawing to show what i mean

whipped it up just for you. I don't make sammiches... I make parts drawings. ;D

 

When I went from the old gas system (on my first XCR) to the new gas system, I took those weights out.

Just to look at 'em, while I had everything apart, torque wrench in hand.

Dunno if it was the fact mine had several thousand rounds down the barrel or what, but they were coated in a black substance that inhibited movement. Maybe penetrating oil? I dunno.

In any case, they didn't rattle - and even if they did, it's not enough to concern me.

 

One thing I've been curious about on the AK, and now on the XCR, is how plenty of fouling gets seemingly around the piston and onto the recoil spring. I've got to presume that some fouling is getting through the piston somehow, but sure can't visualize it.

 

What do you mean through the piston,as in into the action,or inside the piston?

 

The recoil spring, which appears mostly contained within the piston (especially during recoil when carbon is flying everywhere) gets plently of crap on it. Wipe it down wth a Hoppes patch after firing 100 rounds, and that patch will come up black. There is literally more crap on it than there is on the bolt.

I noticed the same thing with AKs long ago, and always wondered how this happens.

 

On the XCR as well as the AK what I think happen is that because the piston does not have any compression rings as would an internal combustion engine,there is considerable blow-by of the burnt rapidly expanded powder gases.The fit of the gas tube and piston is also very loose,the whole point of which is that unused,unneeded gases are blown out of the gastube through holes in the upper.Obviously because of the "not very snug " fit of the piston and gas tube,not all the gas will go out of the tube but will find it way around the piston and down to the recoil spring area.Not a big deal as most of the gas is contained in the piston area,and not taking a dump onto the bolt/carrier and chamber area.