should a 3/8ths (16 tpi) diameter grade 8 bolt be torqued to?

I just broke two at 70lbs (with lube), is it me or the bolts? Have I just been lucky all these years?

http://www.team.net/sol/tech/torque.html

This might answer your question.

2112,
I think you have been very lucky ! ARP's 3/8 fine thread rod bolts are only torqued to 50lbs. Stock Chevy 3/8 rod bolts 45 lbs, and both of those are far better than grade 8.

Here is a guide I found with a Google search:

http://www.dansmc.com/torque_chart.htm

If the bolts are specific to a particular application you should always use the manufacturers torque specs.

Hope this helps,

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Wow,

Very helpful. I have been lucky!

Thanks

Where did you come up with the 70 ft lbs?

A well respected machinist. Upon reflection, I probably transposed the numbers and have been doing it for some time, luckily without a problem.
Being in a non-stressed application was probably helpful.

In a related question, is an overtorqued bolt shot?

yep. Probably strecthed past its's elasticity point.

Cheap insurance not to reuse a bolt your unsure of. In the offroad trucks we use to throw away every suspension bolt after a race just to be safe.

Torque is usually set to 75% of breaking point.

Also good information.

Had some flywheel bolts that I torqued to 95lbs with moly, reread the spec sheet, 95 with oil 75 with moly.

Tossed them to be safe though they sure looked good