How to tell which end of rod knock?

[clytle374]

If it is an US model 300D the pump is a Bosch MW.  The timing is set on the pump by shims under the flange on top of each pump element and balancing is done by turning the element.  DO NOT loosen the 2 bolts holding down each element.  If that has been done, it needs to go(with lots of cash) to someone with a test bench.

The delivery valve usually causes smoking before other problems on these cars, but could cause the problem.  They are available from the dealer and are easy to change.  They can be swapped from cylinder to cylinder just fine to diagnose the knock. 

IIRC they need to be replaced in sets since they were up dated several times and good luck matching a new one to the set.

BTW Mercedes sells the whole W123 (up to 1985 300D, 240D, etc, and all gas models of that chassis) for $20 on a cdrom.  Must have if you have one of these cars.