checking big end clearance

Rebuilding my '74 850 and I'll be putting in new connecting rod bearings. What's the recommended clearance, and the best way to check it? Will Plastigage do it?

Thanks

It's best to carefully mic the journal in several places and compare the readings with the specifications in your manual. If found out of tolerance, have the journal ground to the next size smaller.

Then use plasti-gage (sp?) as a final inspection to verify clearance between journal and bearing shell. I can't remember what the clearance is supposed to be, but it's something like 0.0015"-- check your manual.

The correct clearance is .001, the range is .00085 to .0014. The Norton workshop manual suggest that you have the crank turned when the clearance exceeds .0015. Plastiguage is good for a general view, but keep in mind that the correct geometry has slightly less clearance on the side of the rods, think of them as slightly oval, so the clearance where the bearing shells mate would be a tenth to 2 tenths less, a set of precision instruments are recommended. This is appropriate because the lesser clearance, in this area, keeps the rod square with the journal, and at comparably less stress than the top and bottom of the big end that carry the oil film and take the brunt of the force.

RS