Shane661
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posted June 09, 2009 03:16 AM
 Edited By: Shane661 on 9 Jun 2009 11:18
Oil Pressure & Bearing Clearances
Are bearing clearances set with a certain oil pressure in mind? I have seen something about the way that bearing clearances affect how the oil is "dispersed" across the bearing surface. So, with this in mind, would changing your oil pressure change the ideal clearances??
How does oil viscosity affect this "dispersion"?? Would high oil pressure and low viscosity be a recipe for disaster?
Is there an "engine building for dummies" book out there? 
Shane
  
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Y2KZX12R
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posted June 09, 2009 04:13 AM
Edited By: Y2KZX12R on 9 Jun 2009 12:18
Shane, Yes. Clearance, viscosity and volume all go hand in hand.
The engineers when designing an engine take into account the bearing surface area, the load, the rpm, the clearance, the oil pressure seen at the bearing, the volume of oil past the bearing etc.
The volume of the pump, the bearing clearance and the viscosity determine the flow for cooling the crank and rods. Cooling is the main function of the engine oil, not lubrication.
If you increase the bearing clearance you flow more oil.
If you lower the viscosity you flow more oil.
If you increase the oil pump volume you flow more oil.
All 3 will cool the crank and rods more. All three can cost HP due to either added windage and or an increase in HP required to run the oil pump.
For LSR Karl has the right idea. If you increase the oil flow past the bearings at high engine speed by raising the oil pressure relief valves poping pressure, you provide more oil/cooling to the crank and rods at high rpms where the presssure may have been bleeding off. But it will most likely cost some HP.
Many people think that using a higher viscosity oil to get more oil pressure is "better" for the engine. But oil pressure is simply a measurement of the resistance of flow. Oil pressure goes up because thicker oil cant flow as much at any given temp. So the flow past the bearings is reduced, as is the cooling of the crank and rods.
So a good trade off is increasing the bearing clearances and then running a thicker oil.
Or, increasing the bearing clearances and increasing the oil pump volume and using the same viscosity oil.
So yes the relationship of all three is important.
On these bikes its hard to change the oil pump volume per rotation. You can also change the oil pump rotations per crank rotation to gain volume, but thats not easy as well.
Both are difficult to change so we are stuck playing with clearances and viscosity for the most part.
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Y2KZX12R
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NOX
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posted June 09, 2009 05:39 AM
Very good informative answer here........
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dougmeyer
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posted June 09, 2009 06:14 AM
Edited By: dougmeyer on 9 Jun 2009 14:15
quote:
Is there an "engine building for dummies" book out there?
You're reading it!
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It's not that I think you're dumb, it's just that so much of what you know isn't true....
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Dane
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posted June 09, 2009 06:28 AM
quote:
Very good informative answer here........
+1
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NINJA12
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posted June 09, 2009 11:51 AM
I'm sitting in class, learning more from this board than the instructor.
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dubious
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posted June 09, 2009 10:45 PM
quote:
quote:
Is there an "engine building for dummies" book out there?
You're reading it!
Isn't that the truth!
This forum is awesome, but the guys on it are even better.... they make it what it is.
Just another thanks out to everyone here.
Just think, only 10-12 years ago it would have been next to impossible to gain access to all this knowledge!
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