Main bearing clearance
#1
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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
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
#8
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The Shop measured before cutting the crank.And they measured the mains with a dial bore indicator. He cut the crank to the bearings. I verified it after with plastigauge. The crank shop I used only does cranks and is backlogged due to demand for his services. Crank spins with about 5lbs of force (rods attached)
#9
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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.
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.
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Efini~FC3S
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03-07-2014 09:49 PM