motorman1
ArboristSite Operative
Could also be the result of running a 20" bar at speed (high revs) and abruptly putting it into wood. Causes lots of stress on cranks. We broke more than a few 066 / 660's running short bars and pushing them too hard into wood. Same results, cracked cranks. Pretty sure that's why Stihl went to the poly flywheels later. At least that's what I've heard