What will make tow rods bend? I took the 406 back to the engine builder and have it tear it down. The number 5 and 7 guide rods are bent. The pistons are fine and he is taking it down further to check the crank and bearings. So far it looks like its just the two rods. Said that there was odor of like old gas and the rods had a sludge like material on them. Asked how long after it was broken in it sat. It sat little over 2 weeks until I had the days off to install. Put it in, ran like a champ. Its when the distributor got loose and messed up the timing that it went down hill. Question still is- what contributed to the bent rods. Looks like its going to be 300 bills out of pocket. Thats okay because I bought the engine in 06 and there is only a year warranty. This just recently happened about a month ago.
What RPM did you spin it to?
Most likely you floated the valves.
What cam, springs, size valves, and type of piston?
I would imagine a flat top piston right? Tell me what your cam specs are @.050" also. Speaking of the cam, did you check your cam to rod bolt clearance? Once I hear the cam specs I'll know if this may be an issue.