The worn-out components in this video are on a 1987 300D Turbo (OM603.960 engine). The tensioner lever arm bearing was severely worn, causing misalignment of the idler pulley, which caused the belt to ride off the edge of the pulley. Although the aftermarket ÜRO brand belt shock felt normal when compressed & extended by hand, it was unable to sufficiently dampen the movement of the lever arm, despite only having about 8,000 miles on it (the shock was installed by a German car repair shop).
The constant vertical up/down movement of the lever and shock is not normal; the belt "flapping" around is not normal, and the intermittent clicking noise should not be there either. The center bolt in the lever was not loose, the play visible when moved by my finger is entirely from play in the bearing. Note that the plastic caps are missing on both the lever arm, and pulley. The plastic caps are critical on the lever arm and pulley to keep dirt out of the bearings.
A new Genuine Mercedes lever arm was installed with OEM Stabilus shock, INA pulley, and new plastic dust caps. Now the belt is aligned correctly on the pulley, there is almost no vertical movement of either the shock/lever or the belt, and the clicking noise is gone. When revving the engine at the end of the video, you can see the shock move smoothly, and correctly dampen the lever movement.
When replacing the lever arm, make sure to clean oil from the threads in the timing cover, and apply anaerobic sealant to the threads before torqueing to spec. AND, do not forget to install the thick washer between the lever arm and the timing cover. If possible, allow the sealant to set for 24 hours before starting the engine. Do not use anything except anaerobic sealant on the threads. And only install OE (Geniune Mercedes) or OEM replacement parts.
The parts shown in this video are used on the OM601 (4-cyl), OM602 (5-cyl), and OM603 (6-cyl) aluminum-head, SOHC diesel engines produced from approximately 1984 through 1995 worldwide. The parts are slightly different on the DOHC engines (OM604/605/606) introduced around 1994, used in USA from 1995-1999; but the basic design of the belt tensioner is similar both both SOHC and DOHC engines.
