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

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!