Jeez, I guess I am doing it wrong too. I look at Plastigauge as a 'range' measuring tool. Plastigauge is NOT designed nor intended to give you an exact clearance reading. If the Plastigauge is squished out really flat, you know that the clearance on that bearing may not be adequate. Further investigation (inside mics, snap gauges, ect) will be required. The same is true if the Plastigauge is not squished very much.
Plastigauge is just intended to check the bearing manufacturer and crank grinder's work--it is just intended to catch a problem, not be the end/all of bearing clearance measurements.
Inside mics, snap gauges, ect are far more accurate and would be the 'right' way to measure bearing clearances. But there comes a point in ecomomics--how much does a set of inside mics cost? Could someone who is building his first (and maybe only) stovebolt justify the cost of these tools?
Maybe the correct way to handle this would be to have the machinist assemble the short block, but labor is not cheap. Following more of the same logic of not having absolute state of the art tools will preclude the hobbiest from doing any on his own engine work. If I were assembling a race motor or something rare, I would have ALL the neat trick tools to do the job right.
As long as the clearances are right, the motor will not know whether you used Plastigauge or precision measuring tools. It all comes down to individual choice. Yes, precision measuring instruments AND the accompanying skills to use them correctly are superior. If the machinist and bearing manufacturer did their jobs right, I can justify using a $2.00 piece of Plastigauge just to check things one final time rather than several hundred dollars for tools I would only use once. But, I have been doing things wrong all this time, too.
