Condition of main bearings

[pett3227b]

I have a new crankshaft and new main bearings. I have plastigauged the main bearings and the clearance is good. I took a look at the main bearings after taking it back apart. The surface is scuffed up on a couple of them. Looks like areas that are more shiny than others. Wondering if this is a problem or if it is normal.

[rednax]

Did you rotate the crankshaft at all?

[ricky racer]

If the clearances are good, put assembly lube on them, torque the caps down and move on.

[pett3227b]

Yeah I turned the Crankshaft a lot.

[Gary Dotson]

Sounds like you may not have gotten all the parts as clean as they could have been. There is no such thing as too clean, when assembling an engine. Clean everything as much as you possibly can, coat the bearings with assembly lube and assemble. Fine scratches in the tin flash finish won’t be much of a concern.

[Stoffregen Motorsports]

Scuffing on the bearings is normal, but yes, if not clean, it can be caused by debris or sharp edges.

Basic block and rod prep includes sanding or filing the corners and edges of the rod and main bearing saddles. Just lightly to knock off sharp edges. The sharp edges can scratch the back of a bearing as it is being inserted in the saddle and can cause the bearing to sit up instead of being fully seated. Remove the bearings with scuffing and look for scratches or debris on the back of the bearing shell.

Also, there is a theory that you are never supposed to turn a crank backwards. This is based on the process of grinding a crank journal which is directional. SOme think that turning a crank backwards can cause the tiny filaments on the journals to scuff the bearing. I've never put much stock in that theory, but some are adamant.