Crankshafts tend to have more issues. Nowadays 95% of the machining done on a crankshaft is done by CNC mills. Counterweights, flanges and bearing journals are all machined automatically. This makes for a very nice, consistent component. Where most of the Asian cranks “drop the ball” is in the bearing journal finishing. This is still a process done with a large spinning abrasive wheel. Due to the size of the grinding wheel required for final finishing of crankshaft journals, (usually about 3’ in diameter) the wheels are made out of compressed abrasive. Ideally a wheel made with “diamond stones” would be more consistent but due to the size of the wheel required and the cost to make a wheel that big is not practical. Abrasive stones have done a great job for centuries in the finishing of a metal surface. The only area where you can have issues is that the wheel or abrasive stone does not wear evenly. This is a constant situation when grinding a crank. One must repeatedly “dress” the wheel. To “dress” a grinding wheel is a process in where the operator makes sure the wear surface of the grinding wheel is square to the surface it is machining. When a crankshaft is ground too quickly or the wheel is not constantly checked for straightness the grinding wheel will wear more on the edges of the wheel. Because the wheel moves back and forth across the journal the bearing surface is still consistent and flat. The problem is at the edges or radius of the crank. This is where the wheel is not square and the journal surface has taper or “ramps up” just before the radius of the crank. Most people miss this because they measure in the center of the journal (assuming it’s flat all the way across). The journal measures within a tolerance and you are good to go, WRONG! If the journal has taper you will have a MAJOR failure if not addressed.
Chrysler had “backcut radiuses” from the factory. What this means is where the bearing surface ends at the edges, Mother Mopar had a narrow plunge cut on the journal. This allowed for a wide bearing that went right to the edge of the journal. While this is great for production engines, it does create a weak spot or stress riser where cracks will start. Performance cranks have what are called ”full radius” journals. This means there is a continuous radiused transition at the edge of a journal. These journals, with a full radius require a chamfered bearing to properly clear the transition. NOTE: This is where less expensive cranks drop the ball!
