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Bearing Clearance

General engine tech -- Drag Racing to Circle Track

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saleen385
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Bearing Clearance

Post by saleen385 » Sat Jan 11, 2020 4:14 pm

Ok guys a 12cyl. diesel engine with a 10.236in main journal turning 950rpm max 18-1 compression making 4500hp.
What would you run for clearance & what kind of oil pressure?
Thanks

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Re: Bearing Clearance

Post by Kevin Johnson » Sat Jan 11, 2020 4:44 pm

Last edited by Kevin Johnson on Sat Jan 11, 2020 4:49 pm, edited 1 time in total.

engineguyBill
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Re: Bearing Clearance

Post by engineguyBill » Sat Jan 11, 2020 4:46 pm

Best to consult the engine manufacturer for their recommendations on bearing clearance and oil pressure specs. I don't think any of us on a high performance site will have the background and experience to offer you any viable recommendations concerning this issue . . . . . . . . . .
Bill

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"Do what you can, with what you have, where you are."
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Caprimaniac
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Re: Bearing Clearance

Post by Caprimaniac » Sat Jan 11, 2020 5:50 pm

Ship engine?
Maybe stationary powerplant?

Sorry, very little knowledge to share.
How to turn GURU in an instant.....

bentvalves
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Re: Bearing Clearance

Post by bentvalves » Sat Jan 11, 2020 5:53 pm

let us know what you come up with!

.010" oil clearance ?
100psi ?

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Re: Bearing Clearance

Post by BillK » Sat Jan 11, 2020 8:10 pm

Exactly which engine is it ? Make and model ?
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saleen385
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Re: Bearing Clearance

Post by saleen385 » Sun Jan 12, 2020 8:42 pm

Ok, I am not allowed to say what it is. They are running .003 clearance and 90psi. I really feel that is to little clearance and not enough pressure. Engineers say that is enough but we keep having failures.
Was just looking for other opinions.
Thanks

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Re: Bearing Clearance

Post by Kevin Johnson » Sun Jan 12, 2020 8:54 pm

saleen385 wrote:
Sun Jan 12, 2020 8:42 pm
Ok, I am not allowed to say what it is. They are running .003 clearance and 90psi. I really feel that is to little clearance and not enough pressure. Engineers say that is enough but we keep having failures.
Was just looking for other opinions.
Thanks
Check it against the Tribology handbook.

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Re: Bearing Clearance

Post by engineguyBill » Sun Jan 12, 2020 10:51 pm

saleen385 wrote:
Sun Jan 12, 2020 8:42 pm
Ok, I am not allowed to say what it is.
Why are you not allowed to share the make of engine with us? Secret Service project or FBI? Maybe powerplant for Bill & Hillary's yacht?? I smell BS.
Maybe a Cooper-Bessemer pump station type powerplant?? You are not going to get viable answers to your quiry on a high performance engine site, just too many variables. Contact the engine manufacturer or a factory authorized remanufacturer for accurate answers to your questions.

For instance, my recommendation for natural gas fueled pump station 12 cylinder engine with 38.25" bore, 44.50" stroke and 54.125" center to center connecting rods would be .0065" crankshaft oil clearance and 185# of oil pressure. Considering the use of 22.50 gallons of 70# oil in the crankcase.
Bill

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"Do what you can, with what you have, where you are."
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Re: Bearing Clearance

Post by modok » Mon Jan 13, 2020 12:33 am

No less than .0005 per 1 IMO
so, .0055" minimum

.003", no,
.03"mm maybe?! double check your units :shock:

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ptuomov
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Re: Bearing Clearance

Post by ptuomov » Mon Jan 13, 2020 2:34 pm

So 0.05-0.1% of the journal diameter?

For the pressure, one would want to know what the rpm is and how the oil passages run.

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Re: Bearing Clearance

Post by bentvalves » Mon Jan 13, 2020 5:27 pm

guy, the oil pressure has been stated.

apologies....misread above post. rainy dreary monday.

GUY, the RPM has been stated!

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Re: Bearing Clearance

Post by novafornow » Mon Jan 13, 2020 9:18 pm

I have studied this a little and will go out on a limb and say .008 .

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ptuomov
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Re: Bearing Clearance

Post by ptuomov » Mon Jan 13, 2020 9:29 pm

bentvalves wrote:
Mon Jan 13, 2020 5:27 pm
guy, the oil pressure has been stated.

apologies....misread above post. rainy dreary monday.

GUY, the RPM has been stated!
This to me? For oil pressure, very little should oil the mains. However the big question is how do the rod journals get oiled, given the large main journal diameter. At 950 rpm it shouldn’t require a lot of oil pressure even with that big main, compared to say (2.75”*7000rpm)^2.

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Re: Bearing Clearance

Post by Kevin Johnson » Tue Jan 14, 2020 8:27 am

If the engineers are saying the clearance and pressure are correct (presumably these are the OEM recommendations ) and engine failures are occurring regularly then it is logical to examine other possibilities.

If the engine uses a fluid damper then it could be the case that despite appearing okay visually it needs rebuilding or replacement. The article below points out that this is a common cause of heavy duty diesel engine failure.

Good luck.

http://www.engineprofessional.com/artic ... _64-72.pdf

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