Definition of quantal. 1  1 [Latin quanti how many, plural of quantus] : of, relating to, or having only two experimental alternatives (such as dead or alive, all or none) 2  2 [quantum] : of or relating to a quantum.
3. Engine movement. Another symptom of bad or failing engine mounts is an engine that moves in the engine bay. If the engine mounts are in good condition, they should be able to secure the engine firmly in the engine bay.
Over-revving the engine can lead to rod breaks. The revving causes rod failure due to a valve's spring failing or being sucked into the engine. Faulty bearings cause too much play in a crankshaft and stresses the rod. Continued stress causes metal fatigue and eventual rod failure.