Since 2015 my 1981 Mercedes 240D has clattered on start up following an oil change. This apparent valve train noise however subsided the moment the system pressurized, roughly 5-7 seconds. According to Mercedes the 5-7 seconds it took to pressurize was perfectly normal but the clattering was not. Ironically no one pointed to the tensioner as a possible problem.
Understand, the W123 diesels, whether 240 or 300 series engines, do not have hydraulic lifters so there should be nothing to "tick, clatter or tap". The one thing that is hydraulic is the timing chain tensioner.
Changing the timing chain tensioner is not hard and will also potentially restore your timing by a touch, reduce a considerable amount of noise from the engine bay and the biggest thing of all, save other components from being destroyed!
STEP 1
Drain radiator. If you have not changed the coolant in the past 2-3 years, now is the time to service the cooling system. Do a complete flush with new Mercedes coolant. FYI, why do I recommend Mercedes coolant, simple they have proprietary additives that keep the system in good shape for the duration of the 2-3 years it is in the system. Other coolants I have tired have not maintained their clarity on changing as the Mercedes brand has.
STEP 2
Remove the thermostat housing assembly from the head. You will only need to disconnect the short coolant hose shown below. Check this hose for any dry rot and replace if necessary. NOTE: A considerable amount of coolant will flow out when disconnecting.
In addition, I would highly recommend to replace the two bolts holding the thermostat assembly to the head. They pass through the water jacket and will most likely be rotting. Mercedes has them for about $6 ea. Worth the price to not have a broken bolt the next time you have to get into the system.
This is also good time to replace the thermostat if you need a new one.
STEP 3
Remove the 2 bolts and one exhaust manifold nut. NOTE: more than likely this tensioner will be stuck in place and will need to be pried off the side of the head, but if it still has any "spring" left it will pop out.
STEP 4
At this stage you can disassemble and see if you can rebuild the unit. Mercedes has the spring but no longer make several other key components in the system that will more than likely need replacing. I went by way of a new tensioner as I need two parts that were no longer available.
Mercedes-Benz still has the tensioner available for about $330. Febi a German OEM supplier also has them for about $75. I am a big fan of all OEM but in this case I could not see a difference in construction and went with the Febi. Time will tell.
STEP 5
Clean the area around the tensioner hole making sure not to introduce any dirt into the engine.
STEP 6
Place gasket on end of new tensioner and mount. The new tensioner will have much more resistance and will require you to compress it while installing the bolts.
STEP 7
Reinstall cooling system components, and refill system with coolant. Do not use the old coolant.
STEP 8
Run car and listen for any unusual sounds. Check coolant level after engine has cooled.
