Originally Posted by Stretch

I can't say much that will be constructive / specific for the OM601 but I can say that for the M102 (petrol) engine the difference between the 1.8 and 2.0 version is in the head design and the piston design => the cylinder bore is the same.

The 1.8 M102 has ball topped / convex pistons and a head that suits these protrustions. The 2.0 M102 has flat topped pistons and a different shape to the combustion chamber in the head. I've seen pictures of a M102 2.3 engine that has the convex piston design and combustion shape in the head that is similar to the 1.8 design.

So the message is => if the bore diameters are the same - look carefully at the piston design and combustion chamber shapes. Mercedes also made different displacements by fiddling with the unswept volumes and piston shapes rather than just changing bore sizes