Just wondering if anyone can offer any insight as to whether my piston ring gap, and main bearing clearance is "acceptable".
It's a 1.00mm/0.030" overbored A14, with matched appropriate pistons, piston rings and bearings. I have measured 0.025mm for the first main bearing, and according to my Datsun B210 A14 manual on my phone, 0.025mm is the minimum. But I have also read on here, and somewhere else I can't recall, that 0.020mm is the minimum? Just want to make sure it's within an acceptable range.

Top/first piston ring gap from cyl. 1-4 in thou is 13, 14, 14, 15. Second ring gap measured at 16, 15, 16, 17.
This would seem to be out of specification, though I have a friend in Japan with a rebuilt standard-bore A15, with genuine pistons and piston rings, who has similar measurements - cyl. 4 also having more clearance.

Any help is greatly appreciated.

* 0.020mm minimum clearance
* 0.025mm minimum clearance
Either way, your measurement matches the spec -- it's not less than .020 and it's ALSO not less than .025. The maximum clearance is 0.062 and yours is less than that. All good

Quote:0.002" variation among gaps is OK, the factory specs allow a range larger than that

But are they all too tight, or all too loose?

Often when fitting rings you must manually gap them. This involves pushing the down in the cylinder a certain distance (evenly from top), measuring the gap, and if it's too much, filing one end of the ring until the gap is in spec. But first ensure that the bore is within spec. It might be too tight for your pistons (check piston-to-bore clearance)

On the other hand, if your bore is honed-out slightly larger than spec, the ring gaps will be too big

That's for normal rings. You can buy gapless rings, but recent talk is that these make less HP than normal rings ...

That's exactly how I measured them. I haven't measured piston to bore clearance yet as I don't have a dial bore gauge. They seem O.K to me, but I wasn't sure if the specification still applied if they weren't factory pistons and piston rings, and overbored at that.