A couple of weeks ago I was driving home with a warmed up engine. I rounded a corner and aggressively accelerated from 20 MPH to 60 MPH. I heard the sound of the engine change and noticed the mechanical oil pressure gauge was at zero. I shut her down and had her towed home. Upon further review, the rocker shaft for the #2 cylinder was cracked. What would cause this? The push rod is not bent. Any suggestions on additional areas to check? I was going to pull the intake and inspect. I'm trying to decide between attempting repairs or pulling the motor. Thanks in advance for any insight.