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A micrometer and dial bore gauge (and a skilled pair of hands) are more accurate than plastigauge. With the manual gauges it's common practice to measure in multiple places around the diameter, the plastigauge measures only where you put it. You are more likely to find distorted main caps for example when using the old school method.
for most folks, who don't build engines for a living, the plastiguage
is what's gonna happen. for checking concentricity, you have to fit
everything and torque it to specified values, then use the bore gage.
a 2"~4" mitutoyo bore guage is $4,783. the plastiguage is $7.
i've put together motorcycle engines with a 12,000 rpm redline
with plastiguage, and it's always worked for me. if i want to be really
****, i can check it three times, rotating the shaft a third of a turn,
and get a pretty good idea of running fit.
obviously, it won't work on cam bearings, but any shop with the
necessary equipment to replace cam bearings knows how to scrape
and dychem them to check for fit.
All the talk about replacing the heads rather than just the cups. I've not had an issue with them yet. I didn't want to cause an issue. It's definitely still an option, if you guys don't think it will cause a prob. Maybe Mike will chime in on this.