I'm building my engine and it's not the first I've ever done but it's the first that I'm putting a lot of care into.

As such I am getting more things looked over than I have in the past. The biggest being the main bearing journals on the block. This block previously spun a main bearing so it needs to be line honed. No big deal, except I was looking into this and maybe I'm just over complicating it but I can't figure out if I need over or undersized bearings.

I'm only ever going to shoot for 500AWHP so I'm not setting this up super loose. I'd rather not HAVE to run really thick oil since I do like to drive it in the winter some times (daily is a miata, it doesn't 'snow' very well) and it can get a bit cold here.

Maybe someone can shed some light on this for me..
I was looking at ACL's site about bearings and they have 3 sizes, stock, .025mm and .25mm.

My question is, are these for people like me who had to get line honed lets say .25mm so this would keep the stock oil clearance (assuming crank was factory spec of course),
OR
is this for someone who has the factory sized main journals, and just wants an extra .25mm oil clearance?? That seems like a huge oil clearance though..
OR
someone who cut the crank .25mm and wants the factory oil clearance?

I guess what I'm really asking is, if I got these bearings are they .25mm thicker than standard? and is there a difference in bearings for a cut crank vs a line hone?

p.s. I'm not cutting my crank, I'm against it. Line honing from my understanding though is just fine, as long as its not crazy, and you get a bit thicker bearing to make up for it.

 

The main journals are ALWAYS factory sized. When align honing is done, especially on a cap that had a spun bearing, they machine the mating surface of the caps to make them shorter. This reduces the diameter of the journal, they then bolt the cap to the block, and hone the journals back to size. The result is OEM sized journals, and the centerline of the crank is moved upwards (in relation to the deck of the block), so deck height needs to verified when installing pistons, and piston to valve clearance should also be verified on a setup that was previously OK.

The .025mm are for extra oil clearance on stock sized crank, and the .25 is for a crank that has been turned down. You should stick with standard size bearings is you're getting a new, standard size, crank..

 

Fantastic! Thank you so much clarifying that.

I believe the allowed change in deck height is .07"?

Also it may not be as much of a concern as I see it but wouldn't this put a little stress on the oil pump?

If you end up moving the crank up a bit but don't move the oil pump that seems like it would be a bad thing..

 

It just chnges the anlg eof the belt, so maybe a little more pull. But you won't be the first to line hone a 4g63 and there aren't a bunch of reports of failures. Might as well upgrade to ARP main studs since you're getting it align honed anyways...