"What I'm wondering is, what would cause this to be necessary? Is it an indication of a failure that would cause the engine as a whole to be worthless, or is it just a sign of ordinary wear and tear?"

I think you left out a possibility. He is after all, an instructor... he may have done the crank grind as part of a learning experience for the students.

In any case, an .020 under crank doesn't mean the engine actually failed in any catastrophic manner. Someone may have simply ran it low on oil briefly, mucking up the crank throws. And don't forget, the engine is somewhere around 40 years old; for all we know, this could be the 2nd or 3rd rebuild.

Having said all that, you might want to find out if the crank was NDI'd for cracks.

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Gary L - 142E ITB race car, 73 1800ES
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