Ok to start off i had the rough start issue yesterday. When looking at my engine bay i noticed there was a crank pulley with no belt. I thought for sure i had shredded or lost a belt but the gen 3 is beltless so why do we have a crank pulley? Rotational mass? Timing? Or did i miss something?
Mean. <<snicker>> OP: I wondered the same when I first saw it I was told it works as a flywheel. I presume for rotational energy when the ICE no longer needs to rotate.
It is first off a crankshaft -dampener-. Without it you would trash the bearings. Using it to drive belts was the 20th century solution to make the car work. In the 21st century we don't need the belts any longer. Except on those still making obsolete cars.
It is probably a harmonic balancer, aka a crankshaft dampener as mentioned above. Don't lose any sleep over this, and continue to enjoy your Prius.
The same basic engine is used on the Corolla and Matrix, so they probably kept the belt groove features on it for the sake of having a common part. Otherwise, a plain flywheel would probably work.
