timing chain broke ... damage?
this is my first time posting but hopefully people will still help. I just finished replacing the head gasket on my 330i. I started the engine and it ran, I then stopped the car to check the coolant and oil levels before starting again. when I went to start the engine again I heard a pop and it would not start. unfortunatly I turned the engine over many more times to check for fuel and spark. When I took the valve cover off I found that the secondary timing chain had broken (the chain between the camshaft sprockets). It destroyed my tensioner too. The thing that most surprised me was all of the coolant in the head area. It poored out of my vanos unit when I took it off (I assume I will have to rebuild this too now). I had my head surfaced and checked for cracks so I know the head was in good shape.
My question is what could cause these events to transpire. I found little to no information on these problems so I assume they are rare. What could I have done wrong? If the valves and pistons are ok what can I do to avoid these problems again. (I will try to get the head off again tonight) Thanks for any help.