Gas Key Sealant

[curious1]

The take-away for me is; we have the formula for doing the job right. If you're doing a field repair and don't have the right sealant, I get it. But if I'm at my bench I'm going to stick to the proper standard.

Lap the key, ensure both surfaces are clean, apply the Permatex, the OCKS screws, and 58 in lbs of torque. Then stake the carrier key using a MOACKS.

Note; Lightly dipping a straw into the Permatex container and then carefully placing the straw over the gas port hole of the carrier makes a neat circle around the the gas port hole.

After that I run a pipe cleaner through the gas key to remove any excess that may have gotten into the gas pathway.

But did you follow the assemble drawing and stake the opposing sides of the screw simultaneously? Or did you run the screw in on one side at a time putting a side force against the unsupported screw head? Just mentioning it since most videos I have seen do it one screw at a time.

[lysander]

Not on the lmt carrier I changed a key on a few weeks ago...that had screws that were not torqued before staking... Guess whoever assembled it also didn't put sealant on it.

As I stated elsewhere, when the screws are tightened to the proper torque the screws are nearly at the yield limit for the screws. If the screw yields (stretches) the torque will disappear.

The absence of torque on removal is not positive proof of improper assembly. That's why they are staked in the first place.

[rjacobs]

As I stated elsewhere, when the screws are tightened to the proper torque the screws are nearly at the yield limit for the screws. If the screw yields (stretches) the torque will disappear.

The absence of torque on removal is not positive proof of improper assembly. That's why they are staked in the first place.

I said nothing about the absence of torque on removal... quite the opposite it took a good bit of torque to break through the staking(which was done really well).

The key was LOOSE on the carrier... it rattled and had physical movement up and down on the shank of the screws. The screws were never torqued properly to begin with. And they werent overtorqued and broken either, they both came out whole. Was just a shit install from day 1.

[prepare]

But did you follow the assemble drawing and stake the opposing sides of the screw simultaneously? Or did you run the screw in on one side at a time putting a side force against the unsupported screw head? Just mentioning it since most videos I have seen do it one screw at a time.

I did not. I snugged the four screws up, then tightened them on at a time.

[prepare]

As I stated elsewhere, when the screws are tightened to the proper torque the screws are nearly at the yield limit for the screws. If the screw yields (stretches) the torque will disappear.

The absence of torque on removal is not positive proof of improper assembly. That's why they are staked in the first place.

Isn't the yield limit much higher than 58 in lbs on the OCKS screws?

[lysander]

Isn't the yield limit much higher than 58 in lbs on the OCKS screws?

Nope, they're about the same.

In fact, the ASTM A574, will tend to elongate more under the same load than the actual mil-spec screws.

[prepare]

Nope, they're about the same.

In fact, the ASTM A574, will tend to elongate more under the same load than the actual mil-spec screws.

Are these mil-spec screws? McMaster-Carr- Socket Head Cap Screw (Gas Key) 8-32 x ¼ Part No. 91251A190
https://www.mcmaster.com/91251A190/

[lysander]

I said nothing about the absence of torque on removal... quite the opposite it took a good bit of torque to break through the staking(which was done really well).

The key was LOOSE on the carrier... it rattled and had physical movement up and down on the shank of the screws. The screws were never torqued properly to begin with. And they werent overtorqued and broken either, they both came out whole. Was just a shit install from day 1.

If the screws were loose on arrival from the manufacturer, I would have just sent it back rather than mess with it.

[ssc]

Not on the lmt carrier I changed a key on a few weeks ago...that had screws that were not torqued before staking... Guess whoever assembled it also didn't put sealant on it.

I had two LMT BCG's that the keys came loose. No sealant and the staking was substandard. The screws came loose, causing the gas key to move and wiggle. Called LMT and all they said is that it was a "field fix." Said to tighten the screws and hit them with a screwdriver. The guy I spoke with said I could send them to him, but that's all he was going to do and I would be without my BCG's for a few weeks. I am not much of an LMT fan as I have had other issues with them--which I have posted in the past. IG verified some of my thoughts.

Cheers, Steve

[okie]

I personally feel that the gasket sealant is important. That is my unfounded opinion, but it makes sense to me on some level. Maybe it's like the moly grease where it's unlikely to matter if you were to skip it, but maybe it's the secret sauce that makes the difference between a rock solid gas key and one that's going to come off.

One thing I've noticed is that loose gas keys often still have the staking in place, precluding the possibility that the bolts rotated. I think loose gas keys fundamentally stem from bad torque spec, and I think part of that is getting a very consistent mating surface. If gas is leaking, the mating surface probably wasn't great, and neither can the torque be. I can't remember the exact procedure, but you leave the stuff to dry for awhile before bolting the gas key down.

At the end of the day I think it's a crap system that needs to be changed in the next iteration, along with bolt geometry. There has got to be something they can do now to improve upon it. Laser welding, I don't know, something to permanently mate those that doesn't require occult knowledge to get right.