before I read the proper torque specs of 40 inch pounds I tightened some carrier key screws down fairly tight with a allen wrench and staked them the correct way. I wonder if it will actually hurt anything to leave them this way. If had to guess I would say I put about 12 or so foot lbs on them.
well since there staked I dont see much you could do without needing a new key. so shoot it till it breaks then get a new key or complete BCG. Considering LMT tightins everything down way too hard I wouldnt be suprised if they do it to the carrier keys also.
the proper torque range for a barrel is 35 to 80 FT Ibls, my LMT broke at 122 FT pounds. never checked the carrier though.
Maybe someone with more knowledge and first hand experince will chime in.
Rob
I saw someone at the range here locally with sheared off carrier key screws (not to mention what hell of a phugged up stake job) which I believe was the result of over-tightening.
I torque to 55 in lbs and stake/counterstake with a MOACKS and P-MOACKS and have yet to have one come loose on mine or customers rifles. Cheap and foreign made screws do break sometimes during firing. Use good screws and this doesn’t happen. Armalite now recommends 55 in lbs.
Well, Im glad 2 more people with more experince chimed in, I turned out to be wrong.
Thank You gentlemen.
So since he staked the screws and over tightend them, how hard and how is he going to have to remove the screws??? Sorry for the hijack but ive never had this issue and am curiouse for future refrence how to resolve it.
Rob
Ill just have to file off the stakeing job and remove and install a new key and screws. I staked it like Colt does so I dont think I can get the screws out unless i file if dremel off the stake. Now I need to find some good quality keys and screws.
I crank mine down pretty tight, I’m betting that it’s way more than 40 ft lbs. Never had one loosen or break.
Armalite has som einteresting reading on this …
http://www.armalite.com/library/techNotes/tnote47.htm
For years, veteran ArmaLite® assemblers have tightened carrier keys using a simple Allen wrench. This process has been successful.
As we added employees we decided to use calibrated torque wrenches to assure that we secure the key screws to the proper level. The government standard for carrier key torque is 35 to 40 inch pounds, and we secured torque wrenches set to that value. We then noticed an INCREASE in loose carrier keys. It turns out that we had tightened carrier key screws better without the wrench than with it.
The problem is that the government torque values shown in maintenance manuals are too low.
We have examined the engineering data related to the screw itself, and have increased torque to 55 inch pounds to improve carrier key tightness. We recommend that all AR owners make sure that their carrier key screws are secured to this level, especially if their rifles sometimes shows signs of weak or slow cycling.
If your AR “short strokes,” clean the underside of the carrier key and tighten both screws to 55 to 60 inch pounds. Tighten the front screw first. If your rifle isn’t short stroking, just make sure that the screws are tight and restake if needed.
When you tighten pas the torque limits of a fastener it stretches the fastener and can damage it. This can lead to premature breakage due to stress fractures and the like. On an AR, I wouldn’t worry about it if I didn’t snap them off when installing AND it wasn’t a duty rifle. If it’s a rifle for serious use, follow the specs and do it right.
True.
I’d love to know the torque limits of proper mil-spec or 158 Carpenter steel carrier key screws. The Chairborne/WECSOG engineer in me says that it’s likely somewhere around 90-125 in lbs maybe even greater.
Stretching is why I don’t ever just tighten carrier key screws that have become loose. I always replace, torque then stake. On keys that have shot loose I knock off the parkerizing on the bottom of key on a Arkansas/whetstone to ensure the key hasn’t warped which ensures it won’t leak even when reinstalled.