Lubricating the backs of bearings

[Adger Smith]

Interesting Bearing info
https://www.speedperf6rmanc3.com/conten ... arings.pdf

[fabr]

Clean the bearing back side, if it ever touches due to lack of oil, you have a dead engine, coating or not. I don't understand why this thread has lasted.

LOL!!!!!! Maybe because most cannot admit there is more than one way to do something right.

[engineguyBill]

I didn't read all of the posts in this thread, as it was putting me to sleep. But I will say this emphatically - NEVER PUT ANY THING BETWEEN THE BEARING SHELLS AND THE CASE. Automotive shell-style bearings should be installed clean and dry!!!

[In-Tech]

Interesting Bearing info
https://www.speedperf6rmanc3.com/conten ... arings.pdf

Thanks for the link, downloaded and saved

[fabr]

What amuses me about threads like this is the fact that it is all opinion with absolutely no links to any documentation . Real engineering studies documentation bearing out the opinions. FWIW,I have no documentation myself. I have always used the clean and dry method and yes, I was intentionally BSing in my replies to see if anyone would post any documentation showing definitively that there were any negative effects from an oil film between bearing and saddle. There were none. Lots of sincere opinions. Again ,FWIW, I doubt there is any documentation showing any difference in application between dry or oil film. I firmly believe it makes no real world difference other than dry is much easier to keep clean.

Anyone here care to extend this discussion to just what conditions create a spun bearing? I can think of at least one that wasn't mentioned in that very useful link
https://www.speedperf6rmanc3.com/conten ... arings.pdf about bearing failure.

[racear2865]

What amuses me about threads like this is the fact that it is all opinion with absolutely no links to any documentation . Real engineering studies documentation bearing out the opinions. FWIW,I have no documentation myself. I have always used the clean and dry method and yes, I was intentionally BSing in my replies to see if anyone would post any documentation showing definitively that there were any negative effects from an oil film between bearing and saddle. There were none. Lots of sincere opinions. Again ,FWIW, I doubt there is any documentation showing any difference in application between dry or oil film.

Anyone here care to extend this discussion to just what conditions create a spun bearing? I can think of at least one that wasn't mentioned in that very useful link https://www.speedperf6rmanc3.com/conten ... arings.pdf about bearing failure.

what amuses me about several of the above quotes is common in our daily lives. We call it "Conspiracy Theories". Absolutely zero facts to back it up
reed

[Kevin Johnson]

What amuses me about threads like this is the fact that it is all opinion with absolutely no links to any documentation . Real engineering studies documentation bearing out the opinions. ...

[My emphasis]

Page 8 "4.2. Bearing Crush
The bearing crush is modelled without considering the stress distribution due to the bearing spread.
The bearing shell (insert bearing) is considered in perfect contact with the housing ..."

"Perfect contact" would be a term of art and excludes the presence of a lubricant.

THE TRIBOLOGY HANDBOOK
Second edition
Edited by
M. J. NEALE
(>BE, BSc(Eng), DIC, FCGI, WhSch, FEng, FlMechE



A12.6

PRECAUTIONS WHEN FITTING PLAIN BEARINGS
HaIf bearings
(1 ) Ensure cleanliness: between bearing and housing, between
bearing bore and joint face of bearing and
housing, and in oil-ways and oil system.
(2) Check free spread: bearing should be in contact with
housing in region of joint face.
(3) Check nip: tighten bolts, slacken one side to hand tight,
use feeler gauge on housing joint. Tighten bolts and
repeat on other side.
(4) Tighten bolts: to specified stretch or torque.
(5) Check clearance: between journal and assembled bore
with leads or similar, particularly checking for distortions
(IocaI loss of clearance) near oil grooves or
bearing joint face. (For new design of housing conduct
fitting test: measure bore diameter with shaft removed.)
(6) Oil suplface: before turning shaft.

...

[Momus]

What amuses me about threads like this is the fact that it is all opinion with absolutely no links to any documentation . Real engineering studies documentation bearing out the opinions. FWIW,I have no documentation myself. I have always used the clean and dry method and yes, I was intentionally BSing in my replies to see if anyone would post any documentation showing definitively that there were any negative effects from an oil film between bearing and saddle. There were none. Lots of sincere opinions. Again ,FWIW, I doubt there is any documentation showing any difference in application between dry or oil film. I firmly believe it makes no real world difference other than dry is much easier to keep clean.

Anyone here care to extend this discussion to just what conditions create a spun bearing? I can think of at least one that wasn't mentioned in that very useful link
https://www.speedperf6rmanc3.com/conten ... arings.pdf about bearing failure.

In the absence of empirical information, but using pure logic, considering the effect of lubricating the back of bearings will immediately do two things: it will introduce a thin, slippery film between the two surfaces and a there will be change in the heat transfer properties.

How much and to what effect, ate the questions.

[fabr]

What amuses me about threads like this is the fact that it is all opinion with absolutely no links to any documentation . Real engineering studies documentation bearing out the opinions. ...

[My emphasis]

Page 8 "4.2. Bearing Crush
The bearing crush is modelled without considering the stress distribution due to the bearing spread.
The bearing shell (insert bearing) is considered in perfect contact with the housing ..."

"Perfect contact" would be a term of art and excludes the presence of a lubricant.

THE TRIBOLOGY HANDBOOK
Second edition
Edited by
M. J. NEALE
(>BE, BSc(Eng), DIC, FCGI, WhSch, FEng, FlMechE



A12.6

PRECAUTIONS WHEN FITTING PLAIN BEARINGS
HaIf bearings
(1 ) Ensure cleanliness: between bearing and housing, between
bearing bore and joint face of bearing and
housing, and in oil-ways and oil system.
(2) Check free spread: bearing should be in contact with
housing in region of joint face.
(3) Check nip: tighten bolts, slacken one side to hand tight,
use feeler gauge on housing joint. Tighten bolts and
repeat on other side.
(4) Tighten bolts: to specified stretch or torque.
(5) Check clearance: between journal and assembled bore
with leads or similar, particularly checking for distortions
(IocaI loss of clearance) near oil grooves or
bearing joint face. (For new design of housing conduct
fitting test: measure bore diameter with shaft removed.)
(6) Oil suplface: before turning shaft.

...

Nice article and full of info but unless I missed it there was nothing in it concerning this discussion of dry or slight oil film on bearing backs.

[Kevin Johnson]

Nice article and full of info but unless I missed it there was nothing in it concerning this discussion of dry or slight oil film on bearing backs.

It actually mentions the topic several times under the guise of contact between the backing and housing. The universe of discourse of the thread appears to be all possible engine blocks (and rods?) which are constructed of different materials and therefore differing rigidity whilst simultaneously ignoring varying coefficients of thermal expansion. Differing rigidity ranges from "perfectly rigid" (an engineering term of art) to "elastic."

If you are searching the document for "dry or slight oil film on bearing backs" you will be disappointed.

Figure 12.jpg

Conway-Jones (1973) is referred to several times (Conway-Jones, J. M. (1973), Plain bearing form and installation, Handbook of Tribology, Newnes-
Butterworths, London, Neale, M. J., ed.).

"The results presented here are for a coefficient of friction at the interface between the insert and the
housing μ = 0.8, which is the value recommended by Tabor (1973) for steel on steel contact." (Tabor, D. (1973), Frictional properties of materials, Handbook of Tribology, Newnes-Butterworths,
London, Neale, M. J., ed.)

The free copy to download of the tribology handbook contains both references mentioned above.

I have to get back to work.

[fabr]

I don't think what you are presenting has anything to do with the discussion in this topic. I may well be wrong though.

[fabr]

Let's get down to the nitty gritty of real world examples. Can anyone show documented proof of a bearing installed with a slight oil film on the back spun in its' housing due to the oil film. I am willing to bet lack of crush( for various reasons )or the bearing seizing on the shaft was/is the sole cause of a spun bearing. I am sure there are many examples of spun bearings that were installed dry in the housing. That does not mean that dry back installation is wrong by any means. FWIW,does anyone have any info on the torque required to spin a bearing in it's bore with proper crush both dry install or with oil film on the back?

[Momus]

Let's get down to the nitty gritty of real world examples. Can anyone show documented proof of a bearing installed with a slight oil film on the back spun in its' housing due to the oil film. I am willing to bet lack of crush( for various reasons )or the bearing seizing on the shaft was/is the sole cause of a spun bearing. I am sure there are many examples of spun bearings that were installed dry in the housing. That does not mean that dry back installation is wrong by any means. FWIW,does anyone have any info on the torque required to spin a bearing in it's bore with proper crush both dry install or with oil film on the back?

LOl.

Why does a real world example matter?

You can do a thought experiment and come up to the conclusion that adding a lubricious coating that may also impede heat transfer is not only unnecessary but possibly detrimental in a babbit bearing assembly.

Dry and clean.

[fabr]

Then,in other words,you cannot show a single instance of a bearing failure due to a film of engine oil on the back side. There ARE though many,many failures of a clean and dry install. Does that make clean and dry wrong? Of course it doesn't.

[Kevin Johnson]

Fretting damage appears to be the most likely recognized sign of a bearing shell installed with a lubricant on the backing and housing. There is an inverse problem of sorts in that there are multiple possible root causes of this damage. Now the student/gentle-reader is aware that one of those possible root causes is lubricating the back of the shell and/or the housing. To be clear: the lubricant alters the coefficient of friction or 'μ' between the backing and housing ("friction force" in the parlance below).

fretting.jpg

The text below is from an engineering reference from 1990, republished in 2000:
Tribology in Machine Design
T.A. Stolarski
MSc, PhD, DSc, DIC, CEng, MIMechE

Tribology_in_Machine_Design.jpg

Tribology_in_Machine_Design 2.jpg