…or at least there could be.
My brother, a solid mechanical engineer and muscle car devotee, was diagnosing an engine problem and asked me what I though. A customer at his job was reporting sparks coming from one of the pulleys on the front of an engine. This had been seen only a few other times, and the theories my brother heard were just entertaining. The customer had no idea what was going on, how to fix it, or whose fault it was.
When I learned a little more about the engine, and the pulley in particular, it became quite clear what was going on. The pulley, normally a solid circle of metal attached to the engine via a metallic shaft, was made of two separate metal pieces; an outer metal ring and and inner metal pulley, separated by a dielectric (rubber, in this case). If the belt was slipping on the pulley, an electrostatic charge could build up on the outer ring. The charge would have no way to dissipate like it would on a normal pulley. This charge could then arc to the engine block when it was strong enough (which isn’t too difficult, as the block and the pulley are fairly close).
So my brother went on site and sure enough, the belt was loose. A quick touch with the multimeter confirmed that the pulley was acting electrically as a capacitor, and a new (correctly tightened) belt fixed the issue. What’s interesting is that at some point, a mechanical engineer added that rubber ring as a damper without realizing the electrical implications under a common failure mode.
