There is a crank sensor in the front of the engine. When I unplug it the engine will not start, so I am assuming it is working properly. The head may have been changed before I bought it, because there appears to be a vent hose at the rear of the head that conflicts with the knock sensor and both will not hook up at the same time. Only one or the other. When I pulled the old cam sensor out, there was no metal fillings around it. I'm wondering if the timing could be off a tooth, but it runs very well when cam sensor is not connected. Has me stumpted!