Mercedes Coupes/Sedans/Wagons 1974-1984 Repair Guide

Timing Chain Tensioner

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REMOVAL & INSTALLATION4 and 5-Cylinder Engines



See Figures 1 through 5

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Fig. Fig. 1: Exploded view of the timing chain components190D models



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Fig. Fig. 2: Sectional view of the timing chain components190E models



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Fig. Fig. 3: Cross-sectional view of the timing chain tensioner190E models (190D similar)



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Fig. Fig. 4: When removing the timing belt tensioner, unbolt the air conditioning mounting bracket ...



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Fig. Fig. 5: ... then move the air conditioning unit to one side without disconnecting any lines

There are 2 kinds of timing chain tensioners. One uses an O-ring seal and the other a flat gasket. Do not install a flat gasket on a tensioner meant to be used with an O-ring.

Chain tensioners should be replaced as a unit if defective.

  1. Drain the coolant. If the car has air conditioning, disconnect the compressor and mounting bracket and lay it aside. Do not disconnect the refrigerant lines. On diesel engines, drain the coolant from the block.
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CAUTION
When draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.

  1. Remove the thermostat housing.
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  3. Loosen and remove the chain tensioner. Be careful of loose O-rings. On the 190 series you must first remove the tensioner capnut and then the tension spring. The tensioner body can now be unscrewed with an Allen wrench.
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  5. Check the O-rings or gasket and replace if necessary.
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  7. To fill the chain tensioner, place the tensioner (pressure bolt down) in a container of SAE 10 engine oil, at least up to the flat flange. Using a drill press, depress the pressure bolt slowly, about 7-10 times. Be sure this is done slowly and uniformly.
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  9. Install the chain tensioner. Tighten the bolts evenly. Tighten the capnut on the 190 to 51 ft. lbs. (70 Nm).
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V8 Engines

The chain tensioner is connected to the engine oil circuit. Bleeding occurs once oil pressure has been established and the tensioner is filling with oil.

Since December of 1974, a venting hole has been installed in the tensioner to prevent oil foaming. If you have a lot of timing chain noise, use this type of tensioner, which is identified by a white paint dot on the cap.

Service procedures for tensioners and rails on the different V8's are all similar. Arrangement and shape and size of parts however, is slightly different.

  1. On California models, disconnect the line from the tensioner.
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  3. Remove the attaching bolts and remove the tensioner. The inside bolts will probably require a long, straight 6 mm allen key to bypass the exhaust manifold. It is a tight fit.
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  5. Place the tensioner vertically in a container of engine oil. Operate the pressure bolt to fill the tensioner. After filling, it should permit compression very slowly under considerable force. If not, replace the tensioner with a new unit.
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  7. Install the tensioner and tighten the bolts evenly.
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6-Cylinder Engines See Figure 6

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Fig. Fig. 6: Timing chain tensioner components6-cylinder engines

  1. On A/C vehicles, remove the battery. Unbolt the refrigerant compressor and lay it aside. Do not disconnect the refrigerant lines.
  2.  
  3. Remove the plug with a 17 mm allen key.
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  5. Tighten the threaded ring and loosen the ball seat ring.
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  7. Remove the threaded ring.
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  9. Remove the chain tensioner with a 10 mm allen key.
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  11. Be sure the tight side of the chain is tight.
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  13. Compress the tensioner and install the chain tensioner with a 10 mm allen key. Do not bump the allen key or the tensioner will release.
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  15. Screw in the threaded ring and tighten it to 44 ft. lbs.
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  17. Tighten the ball seat ring to 18 ft. lbs. The pressure bolt should jump forward with an audible clock. If it does not, the assembly must be removed and the installation repeated until it does click.
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  19. Install the plug.
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  21. Reinstall the A/C compressor, battery and air cleaner.
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