Confusion around factory crank/block stampings to determine correct bearing grades

Hi guys,

I have a question regarding the use of factory stampings on the block and crank to determine bearing grades to at least get the oil clearances to factory spec (to then determine how much looser I wish to go).

I have a Nissan VR38 block and crank. Both are brand new. Nissan factory workshop manual states use the stampings to get the bearing grades and you're good to go (assuming you want factory clearances).

Problem I have is that when I reference the stampings to the manual to determine the internal diameter measurements, the journal diameter measurements, and the corresponding OEM bearing thickness measurements, I end up with way less oil clearance than minimum factory specifications.

Has anyone else run into this issue? Is my math out?

The way I find my oil clearance is:

Internal diameter minus journal diameter minus both bearing shell halves (thickness). Even without measuring the parts, Nissan's own measurement stamps put me at far tighter clearances than their minimum so I'm confused.

Of note, some people have suggested I only use the thickness of one bearing, rather than two, as Nissan tried to simplify it. My problem is that each half shell on the mains (for example) is 2.5mm. I would have massively excessive oil clearances if I didn't multiply the bearing thicknesses by two in my calculation.

Thoughts?

Cheers,

I'd measure the ID of the bearing (vertical ID so we're not factoring in bearing eccentricity) installed. They're press fitted in by the "crush" built into the bearing so they'll typically not be exactly representative of their free state. Install and measure and find out how the final fit will actually be because you'll know for sure then.