the engine shop only linished the crank this time but the block already had 25 undersize when I pulled it down.

Plastigauge is like $5. Can save you hundreds in bearing damage. Give it a try, it's very easy. You just put an inch of it on each journal and torque all the bearings. Then remove the crank and measure how much the plastic is squished. The hardest part is getting the plastic off the bearings.

The purpose of undersize bearings is for when the crankshaft is re-ground. The purpose is not to "fill in" a worn crankshaft. But it sounds like your crankshaft has already been re-ground, it's already 25 undersize.

I don't have plastigauge cos I'm sure some one will rip me off on it's price. Also grinding the camshaft seems like lunacy to me since they're harder to replace than bearings

Quote:

Sounds good. The 1973 Datsun 1200 Factory Service Manual says:
Quote:

Did you measure with plastiguage to verify it's OK? It should be OK.

The engine builder is supposed to turn the crankshaft (grind the journals smaller) when fitting undersize bearings.

Main Bearings come in STD .25, .50, .75 and 1.00 undersize.

A12 main bearing clearance spec is 0.020" to 0.062" (0.0008 to 0.0020 mm)

Ok so I've gotten another set of bearings to replace the ones I've stuffed up but the clincher of the deal is that the crank and the bearings are too close. They need some minuscule amount off the face to give appropriate oil clearance. Bearing size is 10 thou undersize (.25mm), the crank measures in at 49.701mm.

Is there such a thing as a 12 or 13 thou undersize bearing? or am I right in thinking it's up to the engine builder to make that size out of the bearings