Calculating journal bearing oiling requirements

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Calculating journal bearing oiling requirements

Post by ELS »

I want to calculate the ideal oil flow to a journal bearing, is there a formula or calculator that I can use?

also subquestion related to this; would it be a good idea to then install restriction jets to the oil pump side of the main bearing oiling holes? as to equalize oil flow to the main bearings?
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Re: Calculating journal bearing oiling requirements

Post by Walter R. Malik »

ELS wrote: Sun Jun 19, 2022 9:27 am I want to calculate the ideal oil flow to a journal bearing, is there a formula or calculator that I can use?

also subquestion related to this; would it be a good idea to then install restriction jets to the oil pump side of the main bearing oiling holes? as to equalize oil flow to the main bearings?
You are never going to have to much oil going to a journal ... allow the bearing clearance to regulate the amount of flow.
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Re: Calculating journal bearing oiling requirements

Post by RDY4WAR »

GPM = 29.3 x 10^-9(L + .0043(W/D))mD^2N

D = journal diameter (in inches)
L = bearing width (in inches)
m = bearing clearance factor
N = rotational speed
W = bearing load (in pounds)

This will get you your minimum. However, as has been stated, you can't really have too much. There's no benefit to restricting oil flow to a bearing. The viscosity of the oil is the bigger factor as you need a minimum oil film thickness to withstand the bearing load. The wider the clearance, the more viscous the oil needs to be.
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Re: Calculating journal bearing oiling requirements

Post by ELS »

Walter R. Malik wrote: Sun Jun 19, 2022 10:47 am
ELS wrote: Sun Jun 19, 2022 9:27 am I want to calculate the ideal oil flow to a journal bearing, is there a formula or calculator that I can use?

also subquestion related to this; would it be a good idea to then install restriction jets to the oil pump side of the main bearing oiling holes? as to equalize oil flow to the main bearings?
You are never going to have to much oil going to a journal ... allow the bearing clearance to regulate the amount of flow.
too much oil causes excessive friction (but not wear).
and I'm not thinking of reducing oil flow to the mains, just to equalize them. the reason I'm asking for a formula to get the minimum required oil flow to a journal bearing is because in my engine design, if the oil pump drive shaft journals wear even a little bit, oil pressure suffers a lot, (dropping to around 0.4bar pressure at idle, around 2bar at redline)
this is because the supply to this journal bearing is straight from the oil filter and trough a 4mm hole as a restriction, then the oil needs to do a 90 degree turn to get to the main oil gallery
to fix this I will be tapping a carburetor fuel jet in this 4mm hole, but I want some guideline to what size of jet I will put in it, I don't want too little to cause premature wear, nor do I want too big which then defeats the purpose.
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Re: Calculating journal bearing oiling requirements

Post by ELS »

RDY4WAR wrote: Sun Jun 19, 2022 11:47 am GPM = 29.3 x 10^-9(L + .0043(W/D))mD^2N

D = journal diameter (in inches)
L = bearing width (in inches)
m = bearing clearance factor
N = rotational speed
W = bearing load (in pounds)

This will get you your minimum. However, as has been stated, you can't really have too much. There's no benefit to restricting oil flow to a bearing. The viscosity of the oil is the bigger factor as you need a minimum oil film thickness to withstand the bearing load. The wider the clearance, the more viscous the oil needs to be.
what measurement is the rotational speed in? in RPM, Ft/s, m/s?
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Re: Calculating journal bearing oiling requirements

Post by RDY4WAR »

ELS wrote: Sun Jun 19, 2022 11:54 am
RDY4WAR wrote: Sun Jun 19, 2022 11:47 am GPM = 29.3 x 10^-9(L + .0043(W/D))mD^2N

D = journal diameter (in inches)
L = bearing width (in inches)
m = bearing clearance factor
N = rotational speed
W = bearing load (in pounds)

This will get you your minimum. However, as has been stated, you can't really have too much. There's no benefit to restricting oil flow to a bearing. The viscosity of the oil is the bigger factor as you need a minimum oil film thickness to withstand the bearing load. The wider the clearance, the more viscous the oil needs to be.
what measurement is the rotational speed in? in RPM, Ft/s, m/s?
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Re: Calculating journal bearing oiling requirements

Post by Stan Weiss »

RDY4WAR wrote: Sun Jun 19, 2022 11:47 am GPM = 29.3 x 10^-9(L + .0043(W/D))mD^2N

D = journal diameter (in inches)
L = bearing width (in inches)
m = bearing clearance factor
N = rotational speed
W = bearing load (in pounds)

This will get you your minimum. However, as has been stated, you can't really have too much. There's no benefit to restricting oil flow to a bearing. The viscosity of the oil is the bigger factor as you need a minimum oil film thickness to withstand the bearing load. The wider the clearance, the more viscous the oil needs to be.
What have I done wrong?

► 29.3 * 10^-9 * (.5 + .0043 * (1000 / 2.2)) * .002 * 2.2^2 * 9000 = 6.2655119999999999E-006

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Re: Calculating journal bearing oiling requirements

Post by ELS »

Stan Weiss wrote: Sun Jun 19, 2022 12:33 pm
RDY4WAR wrote: Sun Jun 19, 2022 11:47 am GPM = 29.3 x 10^-9(L + .0043(W/D))mD^2N

D = journal diameter (in inches)
L = bearing width (in inches)
m = bearing clearance factor
N = rotational speed
W = bearing load (in pounds)

This will get you your minimum. However, as has been stated, you can't really have too much. There's no benefit to restricting oil flow to a bearing. The viscosity of the oil is the bigger factor as you need a minimum oil film thickness to withstand the bearing load. The wider the clearance, the more viscous the oil needs to be.
What have I done wrong?

► 29.3 * 10^-9 * (.5 + .0043 * (1000 / 2.2)) * .002 * 2.2^2 * 9000 = 6.2655119999999999E-006

Stam
clearance factor is too low, it is the clearance / diameter * 1000
also remember that multiplication takes priority over addition, so multiply .0043*(1000/2.2) first, then at 0.5 :)
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Re: Calculating journal bearing oiling requirements

Post by mag2555 »

The problem in terms of rod and main bearings is never having too much ( other then excess oil from too much rod side clearance) but not enough.

Without fail if some main bearing oil feed runs thru the block have a more turn filled path on the way to the main bearings, then why would you restrict those ?
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Re: Calculating journal bearing oiling requirements

Post by RDY4WAR »

Stan Weiss wrote: Sun Jun 19, 2022 12:33 pm
RDY4WAR wrote: Sun Jun 19, 2022 11:47 am GPM = 29.3 x 10^-9(L + .0043(W/D))mD^2N

D = journal diameter (in inches)
L = bearing width (in inches)
m = bearing clearance factor
N = rotational speed
W = bearing load (in pounds)

This will get you your minimum. However, as has been stated, you can't really have too much. There's no benefit to restricting oil flow to a bearing. The viscosity of the oil is the bigger factor as you need a minimum oil film thickness to withstand the bearing load. The wider the clearance, the more viscous the oil needs to be.
What have I done wrong?

► 29.3 * 10^-9 * (.5 + .0043 * (1000 / 2.2)) * .002 * 2.2^2 * 9000 = 6.2655119999999999E-006

Stam
The clearance factor is incorrect. It's not the clearance itself.

Clearance factor = 1000(2C/D)

C = bearing clearance
D = journal diameter

There's an online calculator for this as well: https://calculator.academy/bearing-oil-flow-calculator/
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Re: Calculating journal bearing oiling requirements

Post by fabr »

mag2555 wrote: Sun Jun 19, 2022 2:06 pm The problem in terms of rod and main bearings is never having too much ( other then excess oil from too much rod side clearance) but not enough.

Without fail if some main bearing oil feed runs thru the block have a more turn filled path on the way to the main bearings, then why would you restrict those ?
Sorry but I can't let this myth be stated without a rebuttal. This is false as "too much" side clearance does not influence oil flow volume past rod or main bearings. Bearing clearance regulates the flow.
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Re: Calculating journal bearing oiling requirements

Post by BCjohnny »

mag2555 wrote: ...... other then excess oil from too much rod side clearance ......


Unfortunately as an accurate statement it's pretty much discredited these days

This article outlines currently perceived wisdom on the subject
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Re: Calculating journal bearing oiling requirements

Post by Walter R. Malik »

ELS wrote: Sun Jun 19, 2022 11:53 am
Walter R. Malik wrote: Sun Jun 19, 2022 10:47 am
ELS wrote: Sun Jun 19, 2022 9:27 am I want to calculate the ideal oil flow to a journal bearing, is there a formula or calculator that I can use?

also subquestion related to this; would it be a good idea to then install restriction jets to the oil pump side of the main bearing oiling holes? as to equalize oil flow to the main bearings?
You are never going to have to much oil going to a journal ... allow the bearing clearance to regulate the amount of flow.
too much oil causes excessive friction (but not wear).
and I'm not thinking of reducing oil flow to the mains, just to equalize them. the reason I'm asking for a formula to get the minimum required oil flow to a journal bearing is because in my engine design, if the oil pump drive shaft journals wear even a little bit, oil pressure suffers a lot, (dropping to around 0.4bar pressure at idle, around 2bar at redline)
this is because the supply to this journal bearing is straight from the oil filter and trough a 4mm hole as a restriction, then the oil needs to do a 90 degree turn to get to the main oil gallery
to fix this I will be tapping a carburetor fuel jet in this 4mm hole, but I want some guideline to what size of jet I will put in it, I don't want too little to cause premature wear, nor do I want too big which then defeats the purpose.
If you already have all the answers about this, then why are you asking this question ...?
Probably because you are trying to find justification for what you think ...?
Sorry, I rained on your parade.
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Re: Calculating journal bearing oiling requirements

Post by ELS »

Walter R. Malik wrote: Sun Jun 19, 2022 4:51 pm
ELS wrote: Sun Jun 19, 2022 11:53 am
Walter R. Malik wrote: Sun Jun 19, 2022 10:47 am

You are never going to have to much oil going to a journal ... allow the bearing clearance to regulate the amount of flow.
too much oil causes excessive friction (but not wear).
and I'm not thinking of reducing oil flow to the mains, just to equalize them. the reason I'm asking for a formula to get the minimum required oil flow to a journal bearing is because in my engine design, if the oil pump drive shaft journals wear even a little bit, oil pressure suffers a lot, (dropping to around 0.4bar pressure at idle, around 2bar at redline)
this is because the supply to this journal bearing is straight from the oil filter and trough a 4mm hole as a restriction, then the oil needs to do a 90 degree turn to get to the main oil gallery
to fix this I will be tapping a carburetor fuel jet in this 4mm hole, but I want some guideline to what size of jet I will put in it, I don't want too little to cause premature wear, nor do I want too big which then defeats the purpose.
If you already have all the answers about this, then why are you asking this question ...?
Probably because you are trying to find justification for what you think ...?
Sorry, I rained on your parade.
what?
so because I ask, that means I know the answer already? :lol:
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Re: Calculating journal bearing oiling requirements

Post by Tom Walker »

The old myth about connecting rod side clearance just will not die, or go away it seems.
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