Norm Peterson
corner barstool sitter
I just went out and looked - even the older coarse thread bolts are Grade 10.9, which is roughly equivalent to SAE Grade 8. IOW, it's a pretty good bolt. I can post the picture I took of the bolt head if you like.
"Looking weaker" in this case, is just that. The sharp edges represent a stress concentration, which is not just an increase over the stress you'd get by dividing bolt tension by area. It's also a highly localized area of greater flexibility. Stress intensification factors and flexibility factors are things I occasionally get involved with in my day job, and while this bolt shape is a little different from the shapes of the things I do work with, the basic theory behind it all is going to be the same.
The argument isn't just about breakage. Evidently Mr. Camaro owner put a number of miles on his crappy situation without anything having fallen off the car before he found out what the problem really was.
I think you missed the point. It's the knuckle that's 0.020" thicker. I realize that 0.020" is not a very big change, or much of a gap to have to close up. But if you were to do a deflection analysis of the strut tabs (ears?) I think you'd find that the amount of force required to close the ears up by that 0.020" is in fact enough to matter. Bolt force is torque. Remember, the torque spec only went up by 18 ft-lbs, and consider that whatever amount of torque used to close that 0.020" up to be "wasted" as far as holding the joint together goes.
Even if the crash bolts are Grade 12.9 (which is about 20% stronger than 10.9), that's unlikely to be enough stronger to even buy off the stress intensification factor, never mind the smaller cross section.
Norm
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