Mudflap

I'm ***** deep into my build and just got very accurate measurements of crank diameter and bearing clearance. The clearance is supposed to be 0.8-1.4mils (OEM recommended) and the absolute max is 3.9mils. My gap is measuring 2.7-3.3mils...

As I understand it, a few hps can be found by loosening up that gap. I'm going to guess 2.4mils. But as you get too wide a clearance you lose oil pressure and run the risk of bearing cavitation damaging the bearing surface.

Are there any engine machinist that can shed any light on this? Should I stop worrying and just button her up?

(also, this is a crank that is machined down .02", so I can't change that. And I believe what happened is that my machine shop line honed the mains a little too much.)

Mud

Mazdaspeeder

You could get oversized bearings to close up the gap, no? I run my clearances (at least when assembled) at .002 for rods and mains, using Retella T6 and a Boundary Street/Strip pump with no shims. No problems here. Blackstone oil analysis at every change says so as well

matrussell122

iTrader: (1)

when i had my block machined they set rods and mains at .0025 and i will run a 20w-50

Mudflap

Anyone out there have any anecdotal evidence of a bearing failure due to over clearance? (Doubt it..)

mrmonk7663

iTrader: (9)

Mudflap

Did you measure .0018? Using a dial bore gauge is not trivial. Without some 2 and 3" standards you can't hope to get any accurate results. And you also need decent micrometers 2-3" and 3-4".

Mud

TNTUBA

iTrader: (1)

Old engine builder saying.

Set your clearances slightly too loose and you will know it.

Set them too tight.....and EVERYONE will know it.

mrmonk7663

iTrader: (9)

Mudflap

Too button up this thread (I HATE dead end threads),

Turns out I got the crank machined down (lots of scratches on it) by .020" and got the block line honed. I didn't know this at the time (of course, what I don't know would fill an ocean), but you can't get bearing that are both .001" oversize (due to the line hone) and .020" undersize (due to crank work). You can't do both, you have to choose...

options:
1. You can shim your bearing with .001" strips. Terrible idea. Don't do it.
2. You can get another crank that hasn't been turned down or touched.
3. You can get another block.
4. You can try and convince the machine shop to slightly cut down the main bore halves. But this should be followed with a main bore hone to ensure alignment. And you can't make the width any narrower, just the height of the bore.

Good luck, whoever is reading this.. I'll report back with what I decide to do.

matrussell122

iTrader: (1)

Buy another crank they are cheap