Less than proper octane places a higher load on all parts of the rotating assembly because the ecu retards ignition timing. Piston tdc algorithm will not coincide precisely with ignition timing as per design spec of the ecu. Therefore, as piston is still rising to tdc, ignition is occuring. This increases a downward pressure as the piston is rising to tdc. ie, downward force on the crank, main bearings, and rod bearings. Silent death over time.
Ferd