This is correct, single cylinder four stroke cranks are usually pressed together crankshafts with ball bearing pressed into the cases very similar to a watercraft crankshaft, but most of these engines are used in four wheelers and dirt bikes.There are of course some four stroke single street bikes, usually with an engine fairly common to a dirt bike engine by the same MFG. In those ATV and dirt bike applications a plain bearing crank which is much more susceptible to damage by dirt and contaminates in the oil would not be a good idea, the roller bearing crankshafts are a lot more tolerant of dirt and contaminates in the oil and and take a lot more abuse.All it takes to kill a plain bearing crank is a few grains of sand in the right locations.One more four stroke engine of note that used a roller bearing crank was the KZ1000 street bike, many a drag racing engine was based on this engine because the roller bearing crankshaft in it was damn near bulletproof.
