Just got my H22 running and on its initial run, we noticed a strange noise in the engine and immediately turned it off. Took the car to the garage and checked the timing belt, timing, cam gear and all was perfect. We pulled the head and found that the exhaust/intake valves on piston #3 had touchec each other. So i've got one bent exhaust valve and will have the head taken to the machine shop to have them all checked. My setup is an H22 with JUN cams, valvetrain, stock valves, Type S pistons and a fully ported head with welded chambers and milled slightly around .015. I had 1 degree retard on the exhaust and at dead 0 on the intake side.

What could explain why this happened?