That must be why the lower shell always look the worst? Consider this, if an engine has an excess of clearance in the mains, when you let off the throttle you can or should see the oil pressure resize a little. The lower shells always wear more then the uppers, I garantee it. Also, what produces the most stress in a rotating engine? The load during the combustion cycle while the piston is pushing the crank around after TDC !!! NO one can argue that fact with any intelligence! In over 40 years of working on engines the only time I saw a bearing with the upper shell looking worse then the lower was in a 3406 Cat with a bent crankshaft. In that engine there were a couple of upper shells that looked worse because the crank would lift against the uppers when on the exhaust cycle. If there were any other times a load were present, you would not have an engine producing torque and HP. It would be nothing more then an air compressor. Even so, with either of those, the major load is on the bottom shell period. The only time the load on the upper shells exceeds major lower load on the lower shells is when you are decelerating or going down a hill with your foot off the throttle, at which time the engine becomes a vacuum pump!
