This engine has well known design flaws that cause the rods to bend and the cylinders to oval. Here is post from a well known expert on MB diesel engines in the US. This comes from www.mercedeslist.com. If your particular car already has the factory rebuilt engine, then you are fine. If not run away fast.

This makes some sense. Hydrolocking in some form may be an initiating
> cause. A little leak. A little bend. A little bend. An unbalanced
> load on the cylinder. Then the ovaling begins. Increased ovaling I've
> heard it blamed on dead glow plugs and / or head gasket leaks. While
> the fix your mechanic proposes may be possible, "He says the easy fix to
> prevent it all from happening is to remove the head, pull out the
> piston/rod assemblies (the engine can stay in the car)and replace the
> rods with the newer design now being offered by MB. Install a new head
> gasket and put 'er back together. Painless he says, and it can be done
> in a weekend." if the cylinders are not ovaled. If they are ovaled the
> block is toast (on a Friday no less). A compression test might help
> decide if the preemptive repair was worth trying.

There has been a lot of speculation about the rod bending properties of
the OM603.97 engine (Mercedes is silent on the subject), but despite
it's similarity to all the other Mercedes diesels produced during the
same period, the 603.97 was the ONLY one that developed the bent
rods/oval cylinders - and more than half of them have failed that way.
I have heard of two OM603.96 that have developed bent rods (but not the
ovaled cylinders) and maybe one or two 602.96 engines despite the fact
that MANY, MANY more of these engines were made. Then there is the fact
that once the rods were replaced and the cylinders were rebored and
sleeved, not a single OM603.97 engine has failed the same way. The
modified pistons (and several other modifications) used in early
rebuilds were determine to be of no benefit and were omitted from later
rebuilds.

A compression test is usually worthless until oil consumption is already
noticeably excessive (and by that time you already KNOW what's wrong).
The oil control rings fail to control oil consumption well before there
is any detectable compression loss. Bottom line is that the OM603.97
engine as released from the factory was flawed. The only reliable fix is
to replace the rods and rebore/sleeve the cylinders. Mercedes seems to
have a lock on the rebuilding process. I know of none of the Mercedes
rebuilds that have failed while more than half of the rebuilds done by
dealers, independent mechanics and rebuilders have subsequently failed.

Marshall
--
Marshall Booth (who doesn't respond to unsigned questions)
"der Dieseling Doktor" mbooth@pitt.edu
'87 300TD 182Kmi, '85 190D 2.0 161Kmi, '87 190D 2.5 turbo 237kmi, '84
190D 2.2 229Kmi (retired)


Steve