The second picture in the OP showed the busted off nose of the locating cone still stuck in the bellhousing. Here is a pic of the pilot hole with that piece removed. Seems OK without getting right in there for a closer look.
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This is the hardware: both 7/16" threads. The top hole on the starter is clearly larger then 7/16", but I'm not aware of any bushing that is required and assumed that the pilot hole in the BH was "boss" as far as properly locating the starter. Hopefully that is the case?
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I'm confident that both starters were always tight; The top nut and bottom bolt were still nice and tight when I removed both busted starters. When installing the starters, I always tightened the top and bottom finger tight, then tightened them up evenly with the socket. I never reefed the hell out of them because of the Aluminum trans case but made sure they were good and tight. Before either failure, the secure mounting of the starter was double checked not so much to check for potential movement as to ensure that there was a good ground contact because occasionally the starters would be a bit sluggish when cranking which also seemed odd especially with the new Battery.
The stud was always buried in the BH, so I'm confident things were tightened up properly with sufficient threads available.
No arguing with the presence of the witness marks, but I would imagine that with all of the other damage due to the failures, it wouldn't be out of the question that the witness marks could have also been made at the same time - ie; more of the result then the cause?? Interesting to note that while the mounting surface of the first starter is quite smooth, the surface on the Powermaster piece is finished with very tiny concentric ridges - perhaps to provide better bite on the dust shield?
Hope this is helpful - all the input is appreciated.
