I have a 1993 190 E 2.6. I just replaced/rebuilt head, timing chain, guides, tensioner, etc. How do I set the engine timing? Is the timing set at TDC or some degree? Where are the timing marks on the cam?

M103 engine is set to TDC. Ensure that the balancer (front flywheel) is at TDC marking "0|0", there will be either an indent or pin on the camshaft which must line up with the protrusion on the first camshaft bearing.

Note that your camshaft gear can go on in two different orientations with the normal one being with the arrow on the camshaft gear pointing to the protrusion on the front face of the camshaft. My head has had a lot skimmed of it meaning that the other orientation brings me closer to TDC.

Once TDC has been set rotate the engine twice by hand (720 degrees) and re-check. Always turn the engine clockwise only. Good luck, you'll get the hang of it.