usually clearance is 2 thou, if you are assembling it and the clearance is less sort it out then, dont build it tight, firstly it will bind and could spin a bearing. the gap is there to keep the crank from touching the block using oil to fill it, if you build it too loose oil pressure can suffer unless a higher pressure/volume pump is used.
Yeh know what you mean just trying to work out what has happened to my engine because I had it all built then once it had been running a few Mins the oil pressure would drop right down what could cause this
Tight bearing clearances raise oil pressure, up to the point they are so tight as to wipe out the oil film and metal / metal contact occurs. If you are worried about oil pressure the first thing to do is install a proper, calibrated, MECHANICAL oil gauge reading the main oil gallery pressure. Electric gauges and sender units are notoriously unreliable and senders are often temperature sensitive, unless yo buy high end stuff like Bosch Motorsport, Stack, et cetera. The HKS and most other Jap after market gauges are built for glitz and profit margin, not accuracy and reliability. How are you reading the pressure?
low oil pressure will be two things, bearing clearance to great/oil pump old and worn poor pressure, or faulty oil pressure sender unit. do you know what clearance the bearings were built to, is it a new oil pump?. what make of oil pump, senders do fail alot on these cars too.
The crank should turn freely by hand once the bearings are torqued up. Even good stock oil senders are very slow to react, I've put a greddy press guage in mine and it shows the stock one up. on a fresh built motor its worth hanging a capillary guage over the motor.