SAE Grade-8 bolt snapped @135ft/lbs

[UnAnswerd]

I'm dealing with a critical application. If these fasteners fail, the results could potentially be fatal. I need maximum security. I've been torquing 1/2" grade-8 bolts to 135ft/lbs. Tonight, one of the bolts snapped in half while torquing. This made me rethink all the other bolts that I've been torquing to this spec. First, shouldn't a 1/2" grade-8 bolt withstand far more than 135ft/lbs??? If not, I need a general torque spec that will ensure proper bolt tension. Remember, if these bolts fail or come loose, the results will not be pretty.

Yes, I know that SAE bolts are not used on aircraft, but this isn't an aircraft application. I was however, hoping someone might know....

 

[Tina Fey's Scar]

Are you building a time machine?????? Don't deny it!

 

[Gatorman]

135 FOOT/Pounds!!!???

I would use some loc-tite on the threads

http://www.zerofast.com/torque.htm

See the chart in the link.

 

[UnAnswerd]

135 FOOT/Pounds!!!???

I would use some loc-tite on the threads

http://www.zerofast.com/torque.htm

See the chart in the link.

Hey, thanks for the link. Apparently the proper torque is 116ft/lbs....

 

[qmaster3]

I'm dealing with a critical application. If these fasteners fail, the results could potentially be fatal. I need maximum security. I've been torquing 1/2" grade-8 bolts to 135ft/lbs. Tonight, one of the bolts snapped in half while torquing. This made me rethink all the other bolts that I've been torquing to this spec. First, shouldn't a 1/2" grade-8 bolt withstand far more than 135ft/lbs??? If not, I need a general torque spec that will ensure proper bolt tension. Remember, if these bolts fail or come loose, the results will not be pretty.

Yes, I know that SAE bolts are not used on aircraft, but this isn't an aircraft application. I was however, hoping someone might know....

Just use German torq specs.

 

[Clutch_Cargo]

General torque values:

Grade 8 1/2" dia course thread (13 threads per inch): 95-105 lb-ft
Grade 8 1/2" dia fine thread (20 threads per inch): 113-123 lb-ft

It might take the 135 but once you stretch a bolt beyond it's capacity it won't give you a proper torque reading leading you to keep tightening until you get it or break the bolt. Even if it doesn't break, the first good stress will probably snap it.

 

[UnAnswerd]

Clutch Cargo, thanks for the information.

 

[darkvw]

135 lb/ft isn't that outrageous, the gland nut on my vw is 150 lb/ft, requires a long bar and standing on it as the motor is locked to the bench.

 

[avbug]

Why are you using grade 8 bolts? Use AN hardware and you won't have that problem.

Doing your aircraft parts shopping at home depot, now?

 

[UnAnswerd]

Why are you using grade 8 bolts? Use AN hardware and you won't have that problem.

Why not use SAE grade-8 bolts??? A true grade-8 bolt will yield a tensile-strength of approximately 150,000psi. Though AN hardware may indeed have the same or better values, it is too expensive, not readily available, and quite frankly not even necessary for the application I'm dealing with.

Doing your aircraft parts shopping at home depot, now?

As I said before, this isn't for an aircraft. It's for a truck.