Broken rocker arm???

[dieseldummy]

What would cause a broken rocker arm? I recently rebuilt my engine and after 700 miles and one oil change it started making a "thud" coming from the intake. So I took off the passenger side valve cover and found that one of the rocker arms was broken into two pieces. Luckily the broken off piece hadn't fallen into the motor. After close visual inspection it seems that there were two breaks. The first one looked older and was around the oil hole on the pushrod side. The second was the fresh one and was just an extension of the first. Back to the origional question, why would this be? After the origional 135K and now after another 700 trouble free miles why would it decide to fail? Any ideas and sources for parts would be great.
Thanks,
Justin

[ttpost]

did you replace the rocker arms when you rebuilt it? did you change the cam? more than likely it was just a minor flaw in the rocker that finally broke due to fatigue. or possibly it was too tight? was it possible it was cracked when you rebuilt the motor? just my thoughts :rolleyes:

[dieseldummy]

The rocker was origional. The cam is a Diesel Depot grind, I was told it is the same lift as stock just different duration. Thanks for the info.
Justin