Originally posted by Bryan TTM
i've personally never spun a bearing...i'm not sure i even understand how they spin...they snap in one way only...if you dont mix the caps on the mains or rods...and torque properly...how does a bearing spin unless the rod or crank journal is egged...never understood that

The tabs on the bearing only center it in the rod, they do nothing to hold it in place. Bearing shells are sized slightly larger than the hole they fit in, so when you tighten down on it, everything gets squished. This creates a great deal of friction between the bearing backing and the connecting rod, which holds the bearing in place. When the piston changes direction at the top of the cylinder between the intake and exhaust stroke, the connecting rod goes into tension. The amount of tension at high rpms is so great, the connecting rod bolts stretch like springs. This reduces the amount of squish on the bearing cap, reducing the amount of friction holding it in place and the bearing spins. The amount of crush can be measured, the term used will be crush gap or k-gap. The typical method to measure k-gap is to tighten one connecting rod bolt to full torque while the other is left loose. A gap will open up on the other side and it can be measured with a feeler guage. I have never seen data published on recommended k-gaps for a small block Chevy. The only engines I have done this measurement on were slightly larger than a small block Chevy.