When I did this on mine, I took off the little plastic cover that covers up the fly wheel bolts, and stuck a wooden handle of a hammer in there. That held kept the engine from turning. Then I put a 3 1/2 foot piece of copper pipe over the breaker bar and that bolt came off no problem. Before using the pipe I couldnt budge the thing.
1988 190e 2.3 with 91 engine