Question about Rod Bearing coatings

[cobra]

I am in the midst of a rod bearing job (among other things) and have some questions.

While doing my OEM bearing install, I plasti-gauged the new bearings for record-keeping purposes. On one bearing shell, the plastic strip stuck to the bearing surface instead of the crank and didn't come off easily. I tried carefully removing it by rubbing it with a soft plastic edge and then rubbing it with a cotton cloth. I found that a bunch of black material rubbed off the surface of the bearing and it got very shiny. Did I damage it by doing this? I was EXTREMELY gentle and it still wiped this material right off.

I looked at my old bearings and there is no such coating that can be rubbed off by hand, even with aggressive use of a paper towel. So I am wondering if it's the sacrificial coating for initial start-up?

Secondly, I am curious what these layers are in the attached photo, for educational purposes. Does anyone know what the dark grey and light grey materials are?

Thanks

[Will]

I think it's lead. A nice soft material in case of slight contact.

[Slideways]

It seems there is a light coating on the bearing to protect the surface during packaging and transportation. Some of these OE bearings come with light scuffs from rubbing against the plastic bag they are in. I doubt the BMW techs that did the bearing replacements carefully examined the bearings for scuffs and light scratches on the coating before install. Unless there is a heavy scratch, they are most likely fine. Other bearings, like ACL, come stacked on each other and it does not seem to be an issue.

[cobra]

It seems there is a light coating on the bearing to protect the surface during packaging and transportation. Some of these OE bearings come with light scuffs from rubbing against the plastic bag they are in. I doubt the BMW techs that did the bearing replacements carefully examined the bearings for scuffs and light scratches on the coating before install. Unless there is a heavy scratch, they are most likely fine. Other bearings, like ACL, come stacked on each other and it does not seem to be an issue.

I did notice this on the bearings, light marks from packaging. The top layer is very very delicate.

There are no scratches in the coating whatsoever. I'm mostly concerned about what the black stuff was that I rubbed off and if it's necessary?

[Slideways]

I did notice this on the bearings, light marks from packaging. The top layer is very very delicate.

There are no scratches in the coating whatsoever. I'm mostly concerned about what the black stuff was that I rubbed off and if it's necessary?

Can you post a picture? The coating is a light color, so not sure why it would remove as a darker color.

[cobra]

Can you post a picture? The coating is a light color, so not sure why it would remove as a darker color.

I don't have a picture handy, since it's currently installed (but oil pan is still off). You have a good point but it was definitely black! Looked like graphite to me.

[jbfrancis3]

I thought this was a good article (note there are 3 pgs): https://dsportmag.com/the-tech/the-s...le-complexity/