I have used the cast 4" crank in 2 motors. At the end of the second season, one showed cracking and was replaced with a forged crank. No damage. The other crank showed no cracking occuring and was put back into service. The third race on the cast crank, #5/6 crank pin pulled out and alot of damage occured. These were dirt track motors and saw quite a bit of abuse. There weren't any forged cranks available when these motors were first built, but came available later. The forged crank is still being run after 8+ years. When i recieved the forged crank from MP, I had to turn the mains to correct size and out-of-round problems. I would have expected better with the "good" crank...