So, last 2 days, I've noticed some extra movement in the flex joints in the ex pipe and the valve cover stud is flailing around more. All the bolts seemed tight, but a real close inspection showed movement between the upper frame and lower frame (not a motor mount) . I pulled the bolt, and found a couple munged threads.
It was a 7/16 coarse thread, grade 5 bolt, and a couple threads had deformed allowing movement. The nut looks OK, but it's hard to see inside it!
I went to the local store that claims to be a hardware store, and was only able to get some old dusty grade 5 fine thread bolts & nuts. Tomorrow, I go to the big city (Ukiah) to get some real hardware (structural bolts with extended nuts).
But the question of the day is , what should I get, Coarse or Fine ?
I understand that coarse thread are "tougher to strip" but fine threads leave more meat in the bolt for stronger bolt.
For listeroid applications, what should I search for ? I also believe I should stay with grade 5, being less brittle than 8. Or should I count on the steel frame absorbing shock and not matter about the brittleness ?
Because of the web in the steel I frames, I can't get any larger than 7/16 bolts without the head and nut hitting the web. I had to grind down washers to get them to fit.
layup:
engine bolts to upper frame
upper frame bolts to steel sleepers
steel sleepers clamped to anchors in floor