Stop in for a cup of coffee

Mattax said
Good question.

Looking up the general recomendations on class 12.9 I see 12 to 13 ft lbs as the range published at internet sites.
So 144 in lbs.

Lets try thinking about other possibilities.
Do you still have the broken head?
Lets see a couple close ups.

Maybe it damage before you tightened it down, like a fracture.

Or maybe there was interference and the head wasn't contacting its mating surface.
Classic situation is junk at the bottom of a blind hole or a screw that is too long.
Its why we chase all the female threads
before bolting an engine or transmission together

I ran a tap down thru the bolt holes and blew it out with the air gun. Twice. No I think it was a combination of the torque wrench not being accurate and me not quite having the feel for such low torque. I hung 35 pounds of known weight in 5 pound increments off the handle of the torque wrench before it finally clicked. With it set at 45 inch pounds.

I’ll get pics later this morning. The one just sheered in half, which actually is a good thing cause I wouldn’t have noticed that the other one had stretched and bent