Bearing clearances vs oil viscosity

[gachax]

I've read all the info on oil in SM (including Motor Oil 101 - Dr AE Haas), but I'm still not confident which viscosity oil to use after the break in. I understand the flow vs pressure thing and the benefits of lower viscosity, so I'm not going to argue about that. I've also read that it's acceptable to use thicker oil in case of opening bearing clearances. So the question is what are the exact numbers of clearance vs viscosity?
My bearing clearances are 0.06mm (yes, that's on the widest side of the specs), I've got JE pistons, eagle rods, HKS MHG, ARP head and main studs, full flow thermostat system with 3qt Accusump.
I've been told to use xW-50 or xW-60 oil, because of my mods and because that's what is used for racing engines (I'm not going to drive like a granny, but the car isn't for the daily track use also). It's really hard to fight mechanics about this viscosity topic. Also BMW S54 engine changed their specs for oil from 30 to 60 and bearing clearance from 0.03 to 0.04 in 2001 because of the many bearing failures (it's 0.04mm and viscosity of 60).
I'm sorry this topic has been beaten to death here in SM, but I didn't find the specific info linking the numbers of clearances and viscosity. Thanks in advance.

 

[IJ.]

For what it's worth I found in sustained high 400>low 500rwhp pulls if I ran tight clearences I was seeing some very freaky wear patterns on the main bearings as the block wet noodled all over the place.

I ended up running high side of the spec/low 2 thou clearences and 10/60 synthetic and that solved the issues.

 

[quake]

For what it's worth I found in sustained high 400>low 500rwhp pulls if I ran tight clearences I was seeing some very freaky wear patterns on the main bearings as the block wet noodled all over the place.

I ended up running high side of the spec/low 2 thou clearences and 10/60 synthetic and that solved the issues.

went through the same funny wear patterns and spoke with IJ about this issue. Ended up opening the rods and mains and went with a thicker oil and all was solved. I go about 15-20k between tear downs and bearings look good now

 

[mk3ukr]

I'm sorry this topic has been beaten to death here in SM, but I didn't find the specific info linking the numbers of clearances and viscosity. Thanks in advance.

Actually I never saw this topic of "clearances vs. oil viscosity" discussed, I saw only recommendations to run higher clearances and thicker oil for high hp motors
I will be aiming 0.07mm rods and 0.08mm mains on my new motor and 50 or 60 weight oil.
On my old motor with ~0.04mm clearances was using 0w30 Castrol SLX/Edge

Interesting discussion here http://speedtalk.com/forum/viewtopi...&start=0&sid=d08a930e41bc235f29cd603181e2d1f2

 

[gachax]

Thank you, exactly the answers I was hoping to get .
What about the pressure numbers? It depends on the setup, but how much pressure gain did you get with thicker oil? Or maybe it was compensated by wider clearances...

 

[mk3ukr]

Thank you, exactly the answers I was hoping to get .
What about the pressure numbers? It depends on the setup, but how much pressure gain did you get with thicker oil? Or maybe it was compensated by wider clearances...

We have to ask Ian if he saw increase in pressure with 10w60 oil and 0.002' clearances

 

[jdub]

Thank you, exactly the answers I was hoping to get .
What about the pressure numbers? It depends on the setup, but how much pressure gain did you get with thicker oil? Or maybe it was compensated by wider clearances...

Don't focus on pressure, focus on flow...pressure is resistance to flow. The pressure increase at the gauge will be significant...shimmed pump, thick oil, full flow cooler all will contribute. With your set-up and clearances, the thicker oil should be fine to use....you still want to get the lowest viscosity possible for the cold temp spec. You can use the Accusump as a pre-oiler on start to minimize the effect thick oil will have at start.

 

[IJ.]

No increase noted guys!

Ran my 10psi per 1000rpm goal and made around the 30psi hot idle.

It doesn't get cold here so can't comment on cold flow, even on the coldest day there was no "noise or rattle" indicating a problem.

 

[upgradedsupra]

I had significant knocking/rattle using a 15W-50 on cold start. Car sounded like a diesel.

Duane

 

[IJ.]

That might have been piston slap though D, bottom end rattle has a unique sound (it sounds like $ pissed against a wall)

 

[upgradedsupra]

That might have been piston slap though D, bottom end rattle has a unique sound (it sounds like $ pissed against a wall)

Ian, to clarify, it was during the winter and a different (thinner oil) got rid of most of the rattle.

 

[IJ.]

<nodding> You have real Winter though so no surprise there

 

[upgradedsupra]

<nodding> You have real Winter though so no surprise there

"Real" So you guys just using machines to make fake snow then? :sarcasm:

 

[IJ.]

Rarely gets to 0c here and has only ever snowed twice in my lifetime and melted in minutes.

 

[upgradedsupra]

Rarely gets to 0c here and has only ever snowed twice in my lifetime and melted in minutes.

:cry:

 

[mk3ukr]

No increase noted guys!

Ran my 10psi per 1000rpm goal and made around the 30psi hot idle.

It doesn't get cold here so can't comment on cold flow, even on the coldest day there was no "noise or rattle" indicating a problem.

Ian, what 10w60 oil you are using - Castrol RS?

 

[IJ.]

Castrol Edge.

 

[mk3ukr]

OK, thanks

 

[IJ.]

Very welcome

 

[gaboonviper85]

in that oil 101 dr haas stresses over and over to experiment with your motor....he repeats that you want an oil that will increase 10psi for every 1000rpm's at operating temps! so try to find the oil that works for you and use an oil that goes with your driving style...if you plan on racing alot then your oil temps will rise but if you only plan to piss around town more often then not then thinner oil should be for you....he stresses to try different oils and keep track of what they are doing and use different oil for different purposes....