R107 valve cover mishap

[Calloused]

I changed the valve cover gaskets on my 82 380sl without a problem. When I put everything back together and I turned the engine on there was a kick to the drivers side ever so often. The movement was similar to revving the engine hard but it was moving the car a bit. There was no grinding or abnormal noise coming from it. Then i heard a pop and smoke was coming up from the front of the engine. I rechecked every thing I did and tried it again and it lasted about 2 seconds before another pop and the motor shut off. This time there was a slight hiss from the motor after the pop. How bad did I break the car? I simply replaced the gaskets and did not touch anything else. Any help would be greatly appreciate.