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Old 08-16-2015, 11:52 PM   #1
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Default Oil Clearance Consisitency

I am getting ready to take my motor to the machine shop to get bored and rotating assembly balanced, however I am unsure whether I should maybe get my crank re-ground or just mess around with the bearing sizes.

My crank is in pretty good condition but just slightly .0001" to .0002" out of factory spec. So when I measured my bearing clearances with standard King XP bearings I have too much clearance. I can bring them back into my desired clearance ranges using .001 bearings but the oil clearances would not be consistent with one another, as well some would be about .0001-.0002" outside of my desired range.

I have attached a picture of my spreadsheet with all my numbers. Is it acceptable to use a mix of bearing std and .0005" half on some places and not others to try to get all the numbers close? Or would it be best to just get a re-grind and get .010 bearings?

Also, I am planning on running either a stage 2 or stage 3 boundary engineering oil pump. So that may allow for a slightly looser oil clearance.
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Old 04-24-2016, 10:40 PM   #2
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Bumping, maybe someone might be able to answer this question.

Is it acceptable to use a mix of bearing std and .0005" half on some places and not others to try to get all the numbers close? After measuring clearances after being at the machine shop, two mains I would need +.001 bearings and the others I would need to mix Std and a +.0005" to get roughly consistent clearances?
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Old 04-24-2016, 10:53 PM   #3
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Yes. This is more than acceptable.

When I had a conversation with the King guys at PRI this year, they acted like they weren't going to make .001" bearings. They said their bearings were so precise they didn't need to. I tried to explain to them that it wasn't the bearings being off that I was worried about. I explained that the ability to mix and match 1/2 of a .001" bearing and 1/2 of a std" bearing was a valuable engine building tool and that the inability to do so would keep me with ACL bearings.
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Old 04-25-2016, 06:25 AM   #4
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Mixing shell halves is extremely common. Use the larger shell in the block (top side).

There's a phrase I like when it comes to bearing clearances: "Too small, everyone knows. Too big, only you know."
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Old 04-28-2016, 10:27 AM   #5
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Nevermind, I'm slow.

Last edited by robertcope; 04-28-2016 at 10:59 AM.
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Old 04-28-2016, 12:36 PM   #6
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That's a really neat trick. Is there no risk of side clearance issues because half the bearing is too small? Won't the crank be perpetually near the danger zone on the sides of the smaller half? I'm can think of a great explanation for why this isn't an issue, but I would just be guessing.
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