I’m posting to both share what I just learned (that I suspect many already know) and to get input if I’m wrong. On another post I've shared the story of changing the leaking rope oil seal out for a nos asbestos rope seal. Due to not thinking through the entire process I did create a bit of extra work, but the point of this post is the 1/2 bolt that snapped while torquing the 4 bolts in the #4 main bearing cap.
If you check the 1948 - 1951 Chevrolet Truck Shop Manual, under Engine Assembly 6-17, paragraph 11
HERE, you'll see it calls for all crankshaft bearing cap bolts to be tightened to 100-110 ft. lbs.
I broke one on the number 4 cap (one of 4 bolts on that cap) at very near 105 ft. lbs.
Most queries online agree with the manual and most online responses say all the bolts are 1/2" and the thread count is all over the board.
The images below show what the '51 216 in my original 57k mile truck has in it. Back 4 bolts in #4 cap are 1/2" 13 tpi bolts. The other 6 bolts in the front 3 caps are 9/16th 12 tpi bolts.
I found a very few sources that support the above, and they show the #4 bolts with torque specs generally at 70 to 75 ft.lbs. Some sources spec max of 60 ft lbs.
I now think I know why I broke a 1/2" grade 8 bolt. Installed wet it is not safe at 105 ft. lbs.
RonR
