[Henry Schmidt]

Over the years, we have developed ways to measure parts accurately to determine whether parts need to be replaced, reconditioned or just inspected and cleaned.
There are indeed some "rules of thumb" that guide our evaluation of parts but there are few absolutes when it comes to aline boring a case. Over the years (and still today) we have seen many mag engine cases that did not require aline boring.
Heat is generally the key factor.
Early mag cases that developed low heat generally measure out pretty straight by that I mean well within usable tolerance.