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Case Dimensional Accuracy
Dimensional accuracy is required for high-performance engines. Porsche's machining accuracy was better than most, but it was a long ways from perfect. And the 'modular' construction of the engines, with separate cylinders, added to the possible errors.
We have found (and have had confirmed by others) that the main bearing bores are not always centered between the cylinder seats; variances of up to .007" have been measured.
They are also found to be non-parallel to the cylinder seats; .004" 'tilt' has been measured.
There are several ways of measuring those dimensions accurately, but most require some very expensive tooling. The Case Dimensioning Mandrel requires only a decent depth micrometer to do the same.
If the crank is merely offset in the case, you can compensate by selecting or machining to get short cylinders on the 'long' side of the case. If the crank is not parallel, the only solution is to remove the cylinder studs and machine the cylinder seats normal to the actual crank centerline.
Main bearing bores are similarly measured by various techniques; dial bore gauges are the preferred tool, while inside micrometers will do a good job also. But neither of these will tell you anything about whether the bores are aligned properly.
The Case Dimensioning Mandrel, used with Plastigage, will tell the story about actual dimensions and alignment.