Lubricating the backs of bearings

[hoodeng]

There is a story that goes during WW2, Rolls Royce were under pressure to expand production of their Merlin engine, capacity at RR's facilities were stretched to the maximum and it became apparent that outside manufacturers would have to be enlisted to boost production.

Ford UK was one of them, RR supplied drawings for whatever was required of Ford, according to legend Ford sent them back and informed RR that they weren't accurate enough for their type of mass production. RR would still post hand fit parts after machining to ensure quality, Ford wanted parts to fit only once and that was the first time. I believe Packard also did a spiffing version of the Merlin.

Cheers.

[fabr]

Just for grins and giggles,put a drop of engine oil on a tenths reading mike anvil. Close it using just the friction/ratchet on the thimble. What do you observe?

[hoodeng]

Hi fabr, it is not about the thickness of the oil [it is molecular and won't register on any measuring tools we have], it is about it's effect on dry crush retention.

Cheers.

[fabr]

About 40 years ago I was in the engine machining class that was put on by Dana/Perfect Circle in their facilities atToledo and was headed by Bill McKnight (RIP Bill) and this subject came up. A student asked about this and I remember well what he said. He said the only thing that mattered was that the saddles and bearing backs were clean ,free of any measurable contaminant. A slight film of oil would make no difference and it was a matter of builders choice. He did say that if a builder wished to use a slight film to do it immediately before insertion so no airborn contaminants could land on the surfaces. The slight oil film was of no concern as to the bearing spinning. He said ,and I agree, that if the bearing spun it was due to other factors. The oil film was not the cause. Bearing crush due to correct bore geometry was all that mattered. Dry or slight oil film the crush retention was of no concern.

Consider this,a bearing installed dry will only contact the bearing bore/bearing back on the peaks just like a ring only contacts the cylinder wall on the peaks if dry. The exact same thing is observed if the cylinder is oiled,the ring only contacts the peaks of the bore/ring. Oil is displaced to the valleys.

[modok]

I don't doubt it can work ok, but as for working better in any way that's another story.
oil a morse taper is all I need to say.
It works 100% of the time on people who are familiar with morse tapers.
Some automotive machinists are not, and that's understandable........but oh well, once you get some experience then we can have a discussion about it.
If I can oil my socks and build a good performing engine I don't know what that would prove.

Can I lubricate my socks with some type of oil which prevents ingress of another undesirable type of oil?
......maybe yes, that could totally work, but this has only very limited practical applications.
nine times our of ten, if your feet are going to get oily...then use a type of oil that's good for your feet, or keep them dry. This situation is rare enough that I hope I never need to find out.

[fabr]

A morse taper is not in any sense of the word analogous to this discussion is all I can say.

I did not say either way is better. In fact I do say that dry or slight oil film is equally correct so far as bearing retention is concerned whether it be press fit or crush fit.

Ask 20 machinists if they install replacement valve guides or press fit piston pins dry or with something like Goodsons press fit lube . You will get as many different opinions and another 20 variations of opinions. Never mind the alternatives like shrink fit or heating the small end of the rod methods. My point is that there is definitely more than one way to do things correctly.

[modok]

I'll agree there. When you have to press fit things which could score from friction..... then the lube is usually better than none. The scoring reduces surface contact worse than the lube ever could very often. Scoring holds the surfaces apart, losing contact %, not good for heat transfer and strength.
For the v8 crowd here that would be.... lube on cam bearings, I bet that could be a lively debate.

Far as valve guides, sometimes you can freeze them, thus shrink fit with zero lube, which is maybe a good idea, but getting your valve guides totally stuck is not desirable long term unless you want to be coring them out later. I have totally wrecked a few heads coring out guides, it should work but it can go wrong, that's another subject.

The morse taper is a good example because you want it to lock solid BEFORE it gets oily. Once it gets oily it will not want to lock solid. If it gets oily later usually no problem. What is going on there exactly is debatable but very easy to experience.

I think about it more lately since coming across several engines where over a long time they were in a situation the bearings had virtually no crush at all yet they worked. How is up to speculation, but I am NOt going to conclude that new bearings having zero crush will work the same. Maybe they would maybe they would not but these things that happen Long term, are just difficult to predict and understand.
How two pieces of metal can bond together long term is strange science, takes 3x the force to break it apart VS what it took to seat it, how does that happen? Time, chemistry? LUBE is a huge factor.
There are things that work by this magic and putting lube on them you will be messing with unknown usually not in a good way.

[Kevin Johnson]

Let's discuss how certain individuals have a skin pH level that will cause corrosion on clean finely machined steel surfaces. Way back, this was also an issue for using drafting instruments.

Should non-corrosive gloves be required?

I think the scientific literature is clear that the crush behavior can be non-linear and introducing a lubricant even at the level of a molecular film is a confound. If you have empirical evidence of consistent results then you should be fine so long as the technique and materials are also consistent.

When I went to trade school and worked at my Grandfather's lab, a big issue that came up was technique drift. Workers would gradually and subtly alter their habits while working on one step of a multi-step process with other technicians involved. Clean and dry avoids problems and is difficult to misinterpret.

[Kevin Johnson]

...
How two pieces of metal can bond together long term is strange science, ...

This was a lesson learned in early space exploration. I think every generation or two some of the rules of thumb are forgotten and need to be re-stressed.

[modok]

Yep I've wanted to investigate steering wheel gunk.
Some people they get this gunk build up on the wheel, and I drive and my hands get totally stuck on there, I have to rip them off once a minute, but I think THEY don't experience that or they would clean the gunk off. Strange chemistry.

[modok]

Sorry I feel the need to channel the ghosts of my ancestors but they want to speak
been through this before in many forms.
How on earth does that harmonic damper bolt on the honda/acura take over 600ft-lbs to break loose?
If they had put ONE drop of oil on the faces when it was built then it would not be so stuck

Then there are the cam bolts on subarus.....maybe that rings a bell?


Why are your spark plugs stuck in your head?
Wisest advice I ever hear is to use the dipstick and put ONe drop of oil on the threads.
how does one drop of oil make any difference in a bazillion heat cycles....I don't know, but it does.

All it takes. for better or worse

but we can all agree, and this is the kicker........does putting some oil on it after the fact do anything? Heck no. Does not change a thing. The one drop of oil at assembly does 10x more than soaking it for a week after years have passed.

NGk says put plugs in dry, and cars are long out of warranty before these bolts need to be removed, so maybe they don't care or maybe they don't know. It takes a LONg time to study whatever this is.
Some of the only people have that kind of time are old machinists who work on old machines.

This time it is the opposite! trying to get it stuck, rather than NOT get it stuck.
ONE drop of oil actually does something, It's some type of chemistry.

[lefty o]

ngk puts special magic fairy dust on their plug threads. they are made to go in dry and not have corrosion issues. old fashioned normal plugs, anti seize or a drop of oil on the threads. as for the oil, the carrier of the oil cooks off and leaves behind a film that acts as a barrier.

[Kevin Johnson]

ngk puts special magic fairy dust on their plug threads. ...

I feel confident that fake magic fairy dust will not perform so well. Caveat emptor.

[modok]

yep, I agree. NGK make a great plug but they can get stuck just the same.
love to let this go, but the similarities are glaring

Some bearings are flash plated on the backs, and some aren't
Long term I see no real difference in the engine.
Plating the entire bearing improves shelf life. Same for spark plugs

[In-Tech]

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.