Lubricating the backs of bearings

[steve cowan]

I watched the video,
I want to check for myself if oil behind the bearing shows a bearing crush difference and a bearing/ journal clearance that is actually measurable.
Every engine I have disassembled has had oil behind big end and mains ??
I wonder if the ATF is actually lifting the debris/ excess coating off back of bearing because of high detergent level??
Wipe down a fresh cylinder wall with ATF after you think you have washed and final washed as best as possible, there will be black crap on the rag if wiped with ATF.
I am in agreement of cleaning back of bearing as best as possible even using scotcbrite,mineral turps and compressed air.
I don't think the guy was out to lunch just giving his opinion that's all,I respect that.

[mag2555]

Here's a basic rule of Thumb for the ultimate heat transfer from the Bearing into its housing Bore.

The finish of the Bore should be just as good / fine as the finish on the back sides of your bearings.

Rod big ends are always honed and so should the main line Bore in any block for that same reason in my opinion!

[Circlotron]

I've seen plenty of shade tree types use Loctite on the bearing shells and that stuff sure as hell takes up some clearance.

Back in early '83 I was putting together a 2.2 litre 6 cyl Leyland E series engine for an Austin Kimberley that I bought all in pieces. The thrust bearing was shaped similar to these -> https://www.driftshop.com/acl-trimetal- ... rtina.html and they just wouldn't stay put while the crank was lowered in so I put a bit of cyanoacrylate super glue / krazy glue on the back of them. They now stayed in place alright but the thickness of the film of glue meant no way could you rotate the crank!

[Dave Koehler]

I watched the video,
I want to check for myself if oil behind the bearing shows a bearing crush difference and a bearing/ journal clearance that is actually measurable.
Every engine I have disassembled has had oil behind big end and mains ??
I wonder if the ATF is actually lifting the debris/ excess coating off back of bearing because of high detergent level??
Wipe down a fresh cylinder wall with ATF after you think you have washed and final washed as best as possible, there will be black crap on the rag if wiped with ATF.
I am in agreement of cleaning back of bearing as best as possible even using scotcbrite,mineral turps and compressed air.
I don't think the guy was out to lunch just giving his opinion that's all,I respect that.

Steve,
Lifting the debris assumes there is clearance for that to happen does it not?
For the ATF to flush anything it needs through flow. Where would that come from?
I think some of what we see on disassembly might be due to capillary action where the oil is pulled in there when the press fit is released.
I suppose we should ask a bearing mfg for their thoughts on this controversy.

[BOOT]

The fact that oils gets behind them doesn't suggest anything will flow out really.

Lets think this out you got pressurized oil flowing on the front/face of a rod bearing and being shed on the sides, into the crank or another rod. There is still some pressure(reduced) as it exits and that pressure pushes a bit of oil behind the bearing.

Once the engine is running it's fine, clearances are proven or it soon fails and pump pressure keeps everything happy.

Call it extra insurance or whatever but a clean bearing back makes sense to me.

[Roundybout]

Checking some of the bearing manufacture sites, they all universally say install clean and dry. That’s the way I’ve always done it.

Among the reasons for that recommendation are it can effect bearing crush and heat transfer. All the time invested in getting everything proper and precise can be now thrown off with a little oil on the back of the bearings seems far fetched. I don’t think I’ve ever seen a bearing failure from that direct cause.

[fabr]

FWIW,clean is the main thing and any nonsense about oil/atf/water/whatever flushing out any remaining crud is just BS,IMO. There isn't supposed to be any crud there in the first place. We can argue all day about dry or a small film of oil being best. Again,just my opinion,make sure the things are clean .

[Tom Walker]

I am curious, when we find a film of oil behind the bearing upon disassemble, how and why did it get there?
My gut instinct says capillary action, but I do not have a strong opinion either way. Maybe if detonation or high mileage has allowed the bearing to fatigue and lose some of its conformity?

[hoodeng]

I am interested,,, what is ATF made from?, according to some it is not oil based. That is true of synthetic oils that prevail today like Transmax etc. But that is also true of any synthetic oil replacing any mineral oil in any application.
As far as i have known is that earlier ATF's like Dexron III or Type F were all oil based with additive packages to suit Allison or Ford to name two.

These trans fluids were also compatible with hydraulic ISO 22 and 32 oils and 10W engine oils. I must have committed a lot of sins back in the days when i was servicing heavy plant, there were oils that were designed to go in a number of holes like the Delvac series, [and all holes for Agricastrol].

And no, synthetic trans oils are not slipperier than mineral oils in transmissions.


Anyway....

Clean and dry.

Cheers.

[jake197000]

I think 38ford was last year for full floating bearings

[modok]

If the oil DID lift some dirt out of the low spots in the surface,
how would that be a good thing?

You guys thought yourself into this mess, hopefully you can think yourselves out of it

[ACM]

Wouldn’t filling the asperities or the bearing saddle with a heat transferring fluid such as oïl instead of leaving any foreign matter in them be beneficial ?

[modok]

Your assumption that the oil will improve heat transfer short term or long term VS the dirt that was happily there in the low spots, is questionable, because experience is generally the opposite.
Many instances Installing sleeves, or building spindles, or shrink fitting gears, tapered fits........a dry fit is preferred.
Do you oil a morse taper? hmmmmm?

But, possibly if you used a substance that is good at doing that, I would wonder.
It is plausible, that certain types of lubricant could be used PREVENT the ingress of oil long term and improve heat transfer.

[hoodeng]

RMS, Ra, micron, call it what you will, a engineered, designed to spec, manufactured surface will have a spec of one of the previously mentioned on all surfaces from cast-finish to super-finishing.
In engines all manufactured surfaces have a range of surface finish according to the products function, be it a cylinder bore, pin finish, or, a main tunnel. likewise for the mating parts, a piston skirt finish, ring finish, or, a main shell. It is the matching of the mating surfaces that are manufactured to a specification that will provide the correct interference/clearance, surface cohesion, dimensional range retention.

A part installed as a manufacturer recommends is not a random collection of random opinions but an engineered formula proven to work in service,, some of us might have a different take on what a service manual might recommend, and we may well prove to be as good as [or possibly better!] but when you have no empirical knowledge that transcends those that made a part, go by the book.

Clean and dry.

Cheers.

[modok]

You should see the surface finish on the main bores of this pinto I checked out a few days ago.
grooves like a record, and yet it worked