Mercedes Coupes/Sedans/Wagons 1974-1984 Repair Guide

Valves and Springs

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REMOVAL & INSTALLATION



See Figures 1 through 7



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Fig. Fig. 1: Use a valve spring compressor tool to relieve spring tension from the valve caps



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Fig. Fig. 2: A small magnet will help in removal of the valve keepers



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Fig. Fig. 3: Be careful not to lose the valve keepers



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Fig. Fig. 4: Once the spring has been removed, the O-ring may be removed from the valve stem



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Fig. Fig. 5: A magnet may be helpful in removing the valve keepers



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Fig. Fig. 6: Remove the spring from the valve stem in order to access the seal



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Fig. Fig. 7: Remove the valve stem seal from the cylinder head

  1. Remove the cylinder head. Remove the rocker arms and shafts (all except 190D). Remove the camshaft (190D only).
  2.  

On gasoline engines only:
  1. Using a valve spring compressor, compress the spring and remove the valve cone halves (be careful not to lose the two valve cone halves).
  2.  
  3. Remove the spring retainer and then lift out the spring.
  4.  
  5. Pry off the valve stem oil seal and lift out the lower spring seat (thrust ring). Remove the valve through the bottom of the cylinder head.
  6.  

Then removing the valve stem seal and the thrust ring, a small screwdriver and a magnet may come in handy.

On the 190D:
  1. Remove the hydraulic valve tappet with Special Tool #601 589 05 33 00. After the tappet has been removed, follow the procedures detailed for gasoline engines.
  2.  

On all other diesel engines:
  1. Position an open-end wrench on the valve spring retainer; while holding the retainer, unscrew the capnut with a valve adjusting wrench.
  2.  

A second valve adjusting wrench will be required to hold the counternut while loosening the capnut.

  1. Loosen and remove the counternut.
  2.  
  3. Lift out the valve spring and lower spring seat. Remove the valve through the bottom of the cylinder head.
  4.  

On all engines:
  1. Inspect the valve and spring. Clean the valve guide with a cotton swab and solvent. Inspect the valve guide and seat and check the valve guide-to-stem clearance.
  2.  
  3. Lubricate the valve stem and guide with engine oil. Install the valve into the cylinder head through the bottom and position the lower spring seat (thrust ring).
  4.  
  5. Lubricate the valve stem oil seal with engine oil, slide it down over the stem and then install it into position over the spring seat.
  6.  

When installing seals, always ensure that a small amount of oil is able to pass the seal so as to lubricate the valve guides; otherwise, excessive wear may result.

Intake and exhaust valve stem seals on the 190 series engines are not interchangeable.

  1. Position the valve spring onto the spring seat with the tight coils facing the cylinder head.
  2.  
  3. Install the spring retainer. On all diesel engines (except 190D), the lug on the retainer must be seated in the groove on the valve stem.
  4.  
  5. Further installation is the reverse of the removal procedures detailed previously for the individual engine groups.
  6.  

Tap the installed valve stem lightly with a rubber mallet to ensure a proper fit.

INSPECTION



See Figures 8 through 18



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Fig. Fig. 8: Cross-sectional view of the valve train190E models



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Fig. Fig. 9: Cross-sectional view of the valve train190D models (intake shown; exhaust similar)



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Fig. Fig. 10: Cross-sectional view of the valve trainV8 3.8 engine (all V8 engines are similar)



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Fig. Fig. 11: Exploded view of the valves and related components



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Fig. Fig. 12: Installing the valve assembly



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Fig. Fig. 13: Checking the valve spring free height with a vernier caliper



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Fig. Fig. 14: A dial gauge may be used to check valve stem-to-guide clearance



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Fig. Fig. 15: Valve stems may be rolled on a flat surface to check for bends



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Fig. Fig. 16: Use a caliper gauge to check the valve spring free-length



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Fig. Fig. 17: Check the valve spring for squareness on a flat surface; a carpenter's square can be used



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Fig. Fig. 18: Use a micrometer to check the valve stem diameter

Inspect the valve faces and seats (in the cylinder head) for pits, burned spots and other evidence of poor seating. If the valve face is in such bad shape that the head of the valve must be ground in order to true up the face, discard the valve because the sharp edge will run too hot. The correct angle for valve faces is given in the specification section at the front of this section. It is recommended that any reaming or resurfacing (grinding) be performed by a reputable machine shop.

Check the valve stem for scoring and/or burned spots. If not noticeably scored or damaged, clean the valve stem with a suitable solvent to remove all gum and varnish. Clean the valve guides using a suitable solvent and an expanding wire-type valve guide cleaner (generally available at a local automotive supply store). If you have access to a dial indicator for measuring valve stem-to-guide clearance, mount it so that the stem of the indicator is at a 90- angle to the valve stem and as close to the valve guide as possible. Move the valve off its seat slightly and measure the valve guide-to-stem clearance by rocking the valve back and forth so that the stem actuates the dial indicator. Measure the valve stem using a micrometer, and compare to specifications in order to determine whether the stem or the guide is responsible for the excess clearance. If a dial indicator and a micrometer are not available, take the cylinder head and valves to a reputable machine shop.

Using a steel square, check the squareness of the valve spring. If the spring is out of square more than the maximum allowable, it will require replacement. Check that the spring free height is up to specifications. Measure the distance between the thrust ring and the lower edge of the spring retainer, and compare to specifications.

 
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