"nrp" wrote in message
oups.com...
"Yes, but that wouldn't have sheared the bolt at..."

I agree not sheared but it would have looked like that to the OP. I
would guess a tensile fatigue (probably initiated by bending) with the
crack starting on the side closest to the cyl centerline for cyl 3.

Hm. Most people can detect the crystallization of fatigue as opposed to the
clean cut of a shear. Perhaps not. However, the OP clearly stated that it
was a throughbolt, not a stud.

I agree with the centerline analysis ... those pistons are slapping up and
down a hell of a lot harder than left and right (we hope).



Torque to loosen will be less than torque to tighten, and less
indicative.

Respectfully disagree. WIth torque values of these magnitudes, you will get
very little movement to find the point of actual torque by tightening.
However, just before the nut loosens you will generate very nearly the tight
torque. The problem is to have somebody reading the reverse torque very
carefully and noting the peak while you VERY SLOWLY bring the nut off.

It is, as they say, an interesting (and very expensive) problem in forensic
mechanics.


Jim