SBC - main bearing clearance question

[fabr]

My .02 . Throw the calipers away and get quality mikes and dial bore gauge. There is no way you are getting accurate readings out to 4-5 places with any calipers. You are just kidding yourself if you think otherwise. Repeatable or not

[Belgian1979]

For another motor I built (stock L82) I used the same rule of thumb of .001" per inch crank diameter. So around .0025 for the mains and .0021 for the rods.
Now with this other motor which I sent out to get run in on a dyno they reported that it made no oil pressure. Going to dig into that asap, but a discussion on clearances came up and they were adamant that my above clearances are too big. They refer to the chevy manuals which state
For main 1: .001-.0015"
For 2,3,4: .001-.0023"
For 5: .0025-.0035"

I have also found those in the manuals but so-far I've not ran across anyone using those thight clearances. So what's the deal?

[Dan Timberlake]

To me " no oil pressure " means zero psi.

Was the shop's "no oil pressure" when priming at room temperature?
Or at the first start up at room temperature.

I don't believe An extra .0005" of rod and main bearing clearance by itself would change the running oil pressure by even 1 psi on a typical iron USA V8 from decades past even with a "standard" oil pump.

Actually, for a shop to even suggest that gets my attention, and in a not good way.

[novafornow]

See the above post. Many of us feel that you are not getting accurate data. The devil is in the small things.

[Belgian1979]

See the above post. Many of us feel that you are not getting accurate data. The devil is in the small things.

I agree that they're not giving correct info. I always went with what for instance is mentioned by Clevite and many other manufacturers. That advice will not have been written without reason.
Still stumped about the lack of pressure on that engine though.