Two quick bearing guestions.

[bebbetufs]

I'm ready to install the crank. I have a new set of rod bearings but I would like to reuse the bearing shells for the mains. They show minimal wear and my budget is shot. The crank journals are within "new part" tolerances and no taper (checked with micrometer). The bearing clearances are also well within the "new parts" tolerances (checked with plastigage).

I read this article on how to install bearings. This recommends lightly buffing bearing shell surfaces with Scotch Brite to help the oil flow. I decided to use this method to clean up the mains before reinstalling them.

1. Was this really a good idea, they look slightly rough now?
2. One of the bearings had a small dark spot. The Scotch Brite disloged a particle that must have been embedded there. Now there's a small indentation in the shell surface, possibly between 0.1 - 0.3mm. deep. Is this acceptable?

A photo of rod bearings can be seen in this thread. The mains are in similar shape.

[bebbetufs]

Snapped some photos today. This is the gouge in the main bearing shell.


I then discovered that the thrust bearing journal on the crank looks like this:


And this:

[lindemans]

I am very interested in expert responses here.

I would think that a small crater in the bearing surface would not dramatically impact the distribution of mechanical load; as it has 99% of the surface left. Provided the edges of the crater are not sharp / do not stick out.

It surprises me that appearant minor scoring on these surfaces are no goes in practice.

Any technical analysis on the pics above ?

[Steve@Rennsport]

No worries, mate.

Use them in good health,....

Those bearings are designed for emeddibility so there is not a problem as long as all the clearances are well within spec.

[bebbetufs]

Excellent. That's a boost to my budget!

Any comments on the scoring on the thrust surfaces?
Those belt marks were left by the machine shop after polishing the main journals. The surfaces were silky smooth before.

@lindemanns

It surprises me that appearant minor scoring on these surfaces are no goes in practice.

I'm just a beginner, but according to a friend of mine (engineer) tiny scratches in the surface of highly stressed parts (cranks) are weak spots which can cause fatigue and ultimately failure of the part. I don't think scoring or pitting can cause them to fail, but I suspect pitting could cause cavitation of the oil film?

[Flieger]

Surface finish is not necessarily best when mirror finish. Cross-hatching can actually be flatter to the touch and when compared on a surface finish gauge. You need to check it, not just look.

[bebbetufs]

By checking you mean measuring it with a surface finish gauge?
I'll take it back to the machine shop and have them take a look at it then.

[Steve@Rennsport]

I micropolish each and every crank that goes into an engine and I'd recommend that here.

[bebbetufs]

Thanks for helping me out!

There is only one machine shop in my town (second largest in country) I just had the journals polished by them. I don't think it has been micropolished though. Is this ordinary kind of polishing not to be trusted?

I have spent $320 on polishing so far and expect the machine shop to remove those burrs for free as they were the ones who made them.