when you spin a bearing.. is the crankshaft really spinning the rod bearings around in circle.. or just the bearing is slightly off in the rod cap and touches the crank while the bearing is still stationary? i think this is a good question idk.. thanks for any ideas.

 

Spun bearings are when the rod or main bearing spin with the rod cap/crank journal. the bearings are crescent shaped pieces of metal. (Bearing Image ) when there isn't enough oil to supply the space needed between the crank journal and the rod cap or the crank journal and the main cap the bearing will seize on the crank and follow it's rotation. This is bad for multiple reasons. the most obvious of which would be the metal shavings from the bearings as they spin in the rod cap without oil or the main cap without oil.


Cited from a Mitsubishi site...... but same concept. Hope this answers it.

 

When bearings take a ****, they generally do spin with the crank. However if you catch it early, it may only have a crazy-large clearance gap between the bearing & crank. When that is the case, the bearings tend to distort, and try to hug the crank when removed.

 

ya makes sense..