Main Bearings and measuring my crankshaft

[Delahay]

I have a 87 325is Early production year. The motor is open and I will be replacing the bearings. How do I know if I need standard size or .25? The current ones do not have a stamp on them and I do not have a micrometer tool.

[It's Soda Not Pop]

You could take it to a machine shop and have them measure it.

[digger]

Buy a cheap verniers they will get within 0.25mm for less than $20. Doubt it would be o/s

[e30davie]

I would just get a micrometer. Got to be cheaper than rebuilding the engine twice.

[moatilliatta]

If you're that far along, you'll find another use for the micrometer. Maybe used re cert higher end set, ebay? Mcmaster if you're in a rush.

Probably STD like stated above.

Just note: Full groove main bearings need modified caps to fit if you go that route going back together.

[McGyver]

Buy 1 bearing and plasti-gauge. Measure all your caps with the known value and order the remaining bearings as needed. (or buy the correct tools)

[TobyB]

Inexpensive mics are more than accurate enough-

if you're this far, they're a small percentage of the project cost.

t
it's a slippery slope

[digger]

why do you need a mic for this job? a plastic vernier will tell you within 0.25mm and plasti gauge for the clearance. if you are doing it the professional way you need a mic but also some other bits that are pretty spendy

[TobyB]

Ah- point taken. I went 2 steps farther and assumed OP would want to make
sure the crank was in spec.
The $10 HF digital caliper would be overkill, even.

t
measures twice and then forgets.