I'm sure this topic has been hashed to death before, but what are the opinions of those that have assembled a big block olds or 2 about bearing clearances? On one post I read about these having some deficiency's in oil delivery, then on the next post I read about people saying you need .003"-.004" of clearance on the mains. Here's the plan for what I'm working with, 66' E block that is at he shop now getting line honed/decked/ lifter bushings/bored .06" over with the factory 400 crank that is going to get ground to .02" ish under (on hold till I figure out what the bearing shells measure out to). Rods are going to be H beams from oldsperformance products, and his smaller ring packaged pistons. It's a factory appearing deal, so stock B head castings that are getting the magic touch by a local guy that I have do my cyl heads, factory tri power intake and the factory triple Rochester's, Comp evo roller link bar lifters at .842", and going to have a cam ground to work with the heads once they are done and tested. But it's going to be a street car 91 oct, high 9s compression.

With all that in mind what seems reasonable on clearance? To me .0025"ish on the mains seems like more than enough for this, it's not the big throw 455 that is gonna twist things more, the block and crank are getting freshly machined so the hope is I'm not dealing with old twisted junk. Or is there something specific to these I maybe should know that would compel someone to run a bit more clearance? I'm new to these bbo's but I've built a handful of turbo mitsu 4 cyl's and LS's over the years, we used to sing the mitsu's to 9k with factory cranks and .002"-.0025" of main clearance without issue. My alum block LS has .0015"-.0019" of main clearance and that sees 7800 rpm regularly with a 4" crank stroke.

 

I have always done well using Clevite's recommendation which is a minimum of .001" per inch of journal size. So that would be .0025 on the rods and .003 on the mains minimum. Factory spec according to my engine builders software is .001 to .0037 rods and .0008 to .0038 mains but keep in mind that is for an engine that was not expected to be run at any type of rpm.

I have never seen a little more clearance hurt an engine. Not enough certainly will.

Obviously this will vary depending on intended use.

Just my opinion,

 

My only concern with running more clearance is your sacrificing oil pressure, obviously there's a give and take there, sounds like plenty have run closer to that .003 range and don't fight having low pressure once it's warm.
I also know that having too much main bearing clearance didn't do our rod bearings any favors on the mitsu's, it was like they would leak out the oil instead of getting to the rod bearings.

 

You're comparing apples and oranges here.
I run .0027-.0030 on the rods, .0032-.0035 on mains 1-4. I use the purple spring in the HV pump with a 15-50 or 20-50 oil, no issues.

 

If the clearances are too loose, only the machinist will know. If they are too tight, EVERYONE will know.

If it’s something you plan to run hard, I’d want a little more clearance.

Many years ago on a family vacation I spent a couple hours at Bill Travoto shop. He told me when he first started racing Oldsmobiles he tried all the tricks to keep the bearing intact, with mixed results. His fix was during engine repair/inspection, if he saw any wear on the bearings, he would add a little additional clearance. If nothing touches, there can be no wear. It’s kinda hard to argue with that logic!!