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Let me add some food for thought here. During the time I have been making the reproduction 3.6 engine cases, I got a chance to measure a lot of Porsche cases and we try to measure at least one per month to get a general picture of where the cases are dimensionally. This helps us confirm the accuracy on our cases.
Generally, what I have found is that stock Porsche cases with any kind of mileage at all are usually well out of spec and their tolerances are all over the place. Many engine builders will disagree with this last statement, but many of them are NOT measuring cases with the kind of equipment we have (i.e. 1 micron electronic Renishaw probe on a $275K machine).
This month we measured a 1996 993 case with 65,000 confirmed miles. The case looked almost new, and was one of the nicest I had seen both in and out. I was shocked to find out that after a day of measuring, the main bore was oval and out as high as 2 thou over in many spots.
Remember, the bore spec is 65.000-65.019mm so not a lot of play. On average, this bore was 65.05 and up, and oval in shape.
Also, layshaft center to center of crank bore was also off.
I mention all this because if a low mile late production case is out of spec, then most likely older ones are out of spec as well and many people don't know it.
Out of spec measurements contribute to bearing wear and oil consumption and a host of other problems, and I guarantee you that if your motor is approaching 100K it will be out of spec in at least several places.
The fix for the 993 case we measured is simple - flatten both case halves, rebore the main bore.
Still, it shouldn't be that way and Porsche has, generally speaking, really awful production tolerances on their street cars.
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