Low energy fuse for use in transmitting shock waves. Safety signs as shown can be seen from farther away than conventional signs. The two balancer shafts are divided into areas on both sides of a center line of the cylinder and into upper and lower regions relative to an axis of the crankshaft, and axes of the balancer shafts are arranged so as to be placed within a range of a diameter of the drive gear. In some embodiments, an indication of failure is output when the monitored drive parameter is outside an acceptable range of desired driving parameters during clamping andor firing.