I believe the OM617 is the ONLY non-4-cylinder model in the OM61x engine range that is cast iron! So that's the same as saying its only as good as itself.:p Then again, if you mean in comparison to the OM60x engines, they are just as tough. The OM603 are just as tough as the OM617.

The OM617 is the same as the 4-cylinder models except for an extra cylinder being tacked on.