Mercedes Coupes/Sedans/Wagons 1974-1984 Repair Guide

Cylinder Head

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REMOVAL & INSTALLATION 4 and 5-Cylinder Engines



See Figures 1 through 13

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Fig. Fig. 1: The studs indicated by the arrows are for attaching the rocker cover on 5-cylinder engines



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Fig. Fig. 2: Cylinder head bolt tightening sequence190E models (bolts "a" are tightened to 25 Nm)



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Fig. Fig. 3: Cylinder head bolt tightening sequence190D models (bolts "a" and "b" are tightened to 25 Nm)



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Fig. Fig. 4: Cylinder head bolt tightening sequence 4-cylinder gasoline engines (except 190E)



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Fig. Fig. 5: Cylinder head bolt tightening sequence 4-cylinder diesel engines (except 190D)



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Fig. Fig. 6: Cylinder head bolt tightening sequence 5-cylinder engines (bolts marked "a" are tightened with a Hex bit)



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Fig. Fig. 7: Cylinder head stretch bolt specifications



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Fig. Fig. 8: The cylinder head bolt stretch is measured at dimension "L"



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Fig. Fig. 9: Exploded view of the cylinder head components4-cylinder gasoline engines (except 190E)



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Fig. Fig. 10: Exploded view of the cylinder head components4-cylinder diesel engines (except 190D); 5-cylinder engines are similar



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Fig. Fig. 11: Remove the cylinder head after unfastening the bolts in the proper sequence



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Fig. Fig. 12: Remove the old gasket from the engine block ...



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Fig. Fig. 13: ... then clean the old gasket residue from both mating surfaces

In order to perform a valve job or to inspect cylinder bores for wear, the head must be removed. While this may seem fairly straightforward, some caution must be observed to ensure that valve timing is not disturbed.

  1. Drain the radiator and remove all hoses and wires (tag all wires).
  2.  


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 camshaft cover and associated throttle linkage, then press out the spring clamp from the notch in the rocker arm (all except 190 series).
  2.  

The cylinder head cover on the 190E is removed with the spark plug cables and distributor cap still attached to it.

  1. Push the clamp outward over the ball cap of the rocker, then depress the valve with a large screwdriver and lift the rocker arm out of the ball pin head (all except 190 series).
  2.  
  3. Remove the rocker arm supports (all except 190 series) and the camshaft sprocket nut.
  4.  
  5. On all 5 cyl. engines and the 190E, the rockers and their supports must be removed together.
  6.  
  7. Using a suitable puller, remove the camshaft sprocket, after having first marked the chain, sprocket and cam for ease in assembly.
  8.  
  9. Remove the sprocket and chain and wire it out of the way.
  10.  


WARNING
Make sure the chain is securely wired so that it will not slide down into the engine.

  1. Unbolt the manifolds and exhaust header pipe and push them out of the way.
  2.  
  3. Then loosen the cylinder head hold-down bolts in the reverse order of that shown in torque diagrams for each model. It is good practice to loosen each bolt a little at a time, working round the head, until all are free. This prevents unequal stresses in the metal.
  4.  
  5. Reach into the engine compartment and gradually work the head loose from each end by rocking it. Never, under any circumstances, use a screwdriver between the head and block to pry, as the head will be scarred badly and may be ruined.
  6.  
  7. Installation is the reverse of removal.
  8.  

All diesel engines manufactured after 2/79 utilize cylinder head "stretch" bolts. These bolts undergo a permanent stretch each time they are tightened. When a maximum length is reached, they must be scrapped and replaced with new bolts. When tightening the head bolts on these engines, be sure to follow the steps listed under "Torque Specifications" exactly. Under no circumstances may the older type cylinder head bolts be exchanged with the newer "stretch" bolts.

V8 Engines See Figures 14, 15, 16 and 17

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Fig. Fig. 14: Cylinder head bolt tightening sequenceV8 engines (except 6.9)



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Fig. Fig. 15: Cylinder head bolt tightening sequencemodel 6.9 V8 engines



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Fig. Fig. 16: Exploded view of the cylinder head and related componentsV8 engines



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Fig. Fig. 17: V8 engine cylinder head component keylist

Before removing the cylinder head from a V8, be sure you have the 4 special tools necessary to torque the head bolts; without them it will be impossible. Do not confuse the left and right-hand head gasketsthe left side has 2 attaching holes in the timing chain cover, the right side has only 1 hole. Cylinder heads on the 3.8, 4.5 and 5.0 liter V8's are not interchangeable.

Cylinder heads can only be removed with the engine cold.

  1. Drain the cooling system.
  2.  


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 battery.
  2.  
  3. Remove the air cleaner. Remove the fan and fan shroud.
  4.  
  5. Pull the cable plug from the temperature sensor.
  6.  
  7. On the 6.9, to remove the right-hand head, remove the alternator (with bracket), windshield washer reservoir and bracket and automatic transmission dipstick tube.
  8.  
  9. Detach the vacuum hose from the venturi control unit.
  10.  
  11. Remove the following electrical connections:
    1. injection valves
    2.  
    3. distributor
    4.  
    5. venturi control unit
    6.  
    7. temperature sensor and temperature switch
    8.  
    9. starting valve
    10.  
    11. temperature switch for the auxiliary fan.
    12.  

  12.  
  13. Loosen the ring line on the fuel distributor.
  14.  
  15. Loosen the screws on the injection valves and pressure regulator or mixture regulator. Remove the ring line with the injection valves and pressure regulator.
  16.  
  17. Plug the holes for the injection valves in the cylinder head.
  18.  
  19. Remove the regulating shaft by disconnecting the pull rod and the thrust rod.
  20.  
  21. Remove the ignition cable plug.
  22.  
  23. Loosen the heating connection on the intake manifold.
  24.  
  25. Loosen the vacuum connection for the central lock at the transmission.
  26.  
  27. Remove the oil filler tube from the right-hand cylinder head and remove the temperature connector.
  28.  
  29. Remove the oil pressure gauge line from the left-hand cylinder head.
  30.  
  31. Loosen the coolant connection on the intake manifold.
  32.  
  33. Remove the intake manifold. This is not necessary on 3.8L and 5.0L V8's although the bolts must still be removed.
  34.  
  35. Loosen the alternator belt and remove the alternator and mounting bracket.
  36.  
  37. Remove the electrical connections from the distributor and electronic ignition switchgear.
  38.  
  39. Drain some fluid from the power steering reservoir and disconnect and plug the return hose and high pressure supply line.
  40.  
  41. Disconnect the exhaust system. On 3.8 and 5.0L V8's, you need only remove the manifolds.
  42.  
  43. Loosen the right-hand holder for the engine damper.
  44.  
  45. Remove the right-hand chain tensioner.
  46.  
  47. Matchmark the camshaft, camshaft sprocket, and chain. Remove the camshaft sprocket and chain after removing the cylinder head cover. Be sure to hang the chain and sprocket to prevent it from falling into the timing chain case.
  48.  
  49. Remove the upper slide rail. On 3.8 and 5.0L V8's, remove the distributor and remove the inner slide rail on the left cylinder head. Remove the rail after the camshaft sprocket.
  50.  
  51. Unscrew the cylinder head bolts. This should be done with a cold engine. Unscrew the bolts in the reverse order of the illustrated torque sequences. Unscrew all the bolts a little at a time and proceed in this manner until all the bolts have been removed. On the 6.9, you'll need to raise the engine to remove No. 12 and 18 bolts on the left-side head. To do this, place the level adjusting switch at "S" (first notch).
  52.  

Cylinder head bolts on 3.8 and 5.0L V8's are nickel plated and 10 mm longer than those for previous engines.

  1. Remove the cylinder head. Do not pry on the cylinder head.
  2.  
  3. Remove the cylinder head gasket.
  4.  
  5. Clean the cylinder head and cylinder block joint faces.
  6.  

To install:
  1. Position the cylinder head gasket.
  2.  
  3. Do not confuse the cylinder head gaskets. The left-hand head has two attaching holes in the timing chain cover while the right-hand head has three.
  4.  
  5. Install the cylinder head and torque the bolts according to the illustrated torque sequence.
  6.  
  7. Further installation is the reverse of removal. On 3.8 and 5.0L V8's, insert the rear cam bearing cylinder head bolt before positioning the cylinder head. Also, install the exhaust manifolds only after the cylinder head bolts have been tightened. The camshaft sprocket should be installed so that the flange faces the camshaft. Check the valve clearance and fill the engine with oil. Top up the power steering tank and bleed the power steering system.
  8.  
  9. Run the engine and check for leaks.
  10.  

6-Cylinder Engines See Figures 18, 19, 20 and 21

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Fig. Fig. 18: Exploded view of the DOHC camshaft and related components



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Fig. Fig. 19: Fabricated tools for installing the cylinder head6-cylinder engines



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Fig. Fig. 20: Cylinder head and camshaft housing tightening sequence6-cylinder engines



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Fig. Fig. 21: Make sure the marks on the camshaft and bearing housing are aligned when the engine is at TDC6-cylinder engines

Two people are best for this job. The head must be removed STRAIGHT up. The 2 bolts in the chain case are removed with a magnet.

To install, use 2 pieces of wood 1 /2 inch to 1 1 /2 inch 9 inch to lay the head on while aligning the bolt holes. The exhaust camshaft gear bolt is 0.2 inch shorter.

  1. Completely drain the cooling system.
  2.  


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 air filter.
  2.  
  3. Remove the radiator.
  4.  
  5. Remove the rocker arm cover.
  6.  
  7. Remove the battery. Remove the idler pulley and the holding bracket for the compresser.
  8.  
  9. Remove the compressor and bracket and lay it aside without disconnecting any of the lines.
  10.  


CAUTION
Disconnecting any of the refrigerant lines could result in physical harm.

  1. Unbolt the cover from the camshaft housing.
  2.  
  3. Disconnect the heated water line from the carburetor, the vacuum line on the starter housing, and the distributor vacuum line.
  4.  
  5. Disconnect all electrical connections, water lines, fuel lines, and vacuum lines which are connected to the cylinder head. Tag these for reassembly.
  6.  
  7. Remove the regulating linkage shaft.
  8.  
  9. Remove the EGR line between the exhaust return valve and the exhaust pipe.
  10.  
  11. Disconnect and plug the oil return line at the cylinder head.
  12.  
  13. At the thermostat housing, loosen the hose which passes between the thermostat housing and the water pump. Unscrew the bypass line on the water pump.
  14.  
  15. Loosen the oil dipstick tube from the clamp and bend it slightly sidewards.
  16.  
  17. Unbolt the exhaust pipes from the exhaust manifolds and bracket on the transmission.
  18.  
  19. Force the tension springs out of the rocker arm with a small prybar.
  20.  
  21. Remove all of the rocker arms.
  22.  
  23. Crank the engine to TDC. This can be done with a socket wrench on the crankshaft pulley bolt. The marks on the camshaft sprockets and bearing housings must be aligned.
  24.  
  25. Hold the camshafts and remove the bolt which holds each camshaft gear to the camshaft.
  26.  
  27. Remove the upper slide rail. Knock out the bearing bolts with a puller.
  28.  
  29. Remove the chain tensioner.
  30.  
  31. Push both camshafts toward the rear and remove the camshafts' sprockets.
  32.  
  33. Remove the spacer sleeves on both camshafts. The sleeves are located in front of the camshaft bearings.
  34.  
  35. Remove the guide wheel by unscrewing the plug and removing the bearing bolt.
  36.  
  37. Lift off the timing chain and suspend the chain from the hood with a piece of wire. Pull out the guide gear.
  38.  
  39. Remove the slide rail in the cylinder head by removing the bearing pin with a puller.
  40.  
  41. Loosen the cylinder head bolts in small increments, using the reverse order of the tightening sequence. This should be done on a cold engine to prevent the possibility of head warpage.
  42.  
  43. Pull out the two bolts in the chain case with a magnet. Be careful not to drop the washers.
  44.  
  45. Pull up on the timing chain and force the tensioning rail toward the center of the engine.
  46.  
  47. Lift the cylinder head up in a vertical direction.
  48.  

Mercedes-Benz recommends two people for this job.

  1. Remove the cylinder head gasket and clean the joint faces of the block and head.
  2.  

To install:
  1. Cut two pieces of wood 1 /2 inch to 1- 1 /2 inch 9- 1 /2 inch Lay one piece upright between cylinders 1 and 2; lay the other flat between cylinders 5 and 6.
  2.  
  3. Install the cylinder head in an inclined position so that the timing chain and tensioning rail can be inserted.
  4.  
  5. Lift the cylinder head at the front and remove the front piece of wood toward the exhaust side. Carefully lower the cylinder head until the bolt holes align.
  6.  
  7. Lift the head at the rear so that the board can be moved toward the exhaust side. Carefully lower the cylinder head until all the bolt holes align.
  8.  
  9. Tighten the cylinder head bolts in gradual steps until they are fully tightened. Follow the torque sequence illustrated.
  10.  
  11. Check to be sure that both camshafts rotate freely after the bolts are tight.
  12.  
  13. The remainder of installation is the reverse of removal. Be sure that the spacer for the camshaft gear with the engaging lugs for the vacuum pump drive gear is installed on the exhaust side. Also, the washers for the bolts attaching the camshaft gears to the camshafts must be installed with the domed side against the head of the bolt.
  14.  
  15. Note that the attaching bolt for the exhaust camshaft gear is 0.2 in. shorter.
  16.  
  17. Be sure to adjust the valve clearance and fill the cooling system. Run the engine and check for leaks.
  18.  

CHECKING ENGINE COMPRESSION Gasoline Engines Only



See Figure 22

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Fig. Fig. 22: A screw-in type compression gauge is more accurate and easier to use without an assistant

A noticeable lack of engine power, excessive oil consumption and/or poor fuel mileage measured over an extended period are all indicators of internal engine wear. Worn piston rings, scored and worn cylinder bores, blown head gaskets, sticking or burnt valves and worn valve seats are all possible culprits here. A check of each cylinder's compression will help you locate the problems.

As mentioned in the "Tools and Equipment" portion of Chapter 1 , a screw-in compression gauge is more accurate than the type you simply hold against the spark plug hole, although it takes slightly longer to use (it's worth it). To check compression:

  1. Warm the engine up to operating temperature.
  2.  
  3. Remove spark plugs.
  4.  
  5. Disconnect the high tension wire from the ignition coil.
  6.  
  7. Screw the compression gauge into the No. 1 spark plug hole until the fitting is snug. Be very careful not to crossthread the hole, as most heads are aluminum.
  8.  
  9. Fully open the throttle either by operating the carburetor throttle linkage by hand, or on fuel injected cars having an assistant "floor" the accelerator pedal.
  10.  
  11. Ask your assistant to crank the engine a few times using the ignition switch.
  12.  
  13. Record the highest reading on the gauge, and compare it to the compression specifications. The specs listed are maximum, and a cylinder is usually acceptable if its compression is within about 20 pounds of maximum.
  14.  
  15. Repeat the procedure for the remaining cylinders, recording each cylinder's compression. The difference between each cylinder should be no more than 14 pounds. If a cylinder is unusually low, pour a tablespoon of clean engine oil into the cylinder through the spark plug hole and repeat the compression test. If the compression comes up after adding the oil, it appears that that cylinder's piston rings or bore are damaged or worn. If the pressure remains low, the valves may not be seating properly (a valve job is needed) or the head gasket may be blown near that cylinder.
  16.  

CLEANING & INSPECTION



See Figures 23 through 27

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Fig. Fig. 23: Use a straightedge to check the cylinder head for warpage



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Fig. Fig. 24: A wire brush mounted in a drill can be used to remove carbon from the cylinder head



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Fig. Fig. 25: A wire wheel may be used to clean the combustion chambers of carbon deposits



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Fig. Fig. 26: Check the cylinder head for flatness across the head surface



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Fig. Fig. 27: Checks should be made both straight across the cylinder head and at both diagonals

Carefully chip carbon away from the valve heads, combustion chambers and ports by using a chisel made of hardwood. Remove the remaining deposits with a stiff wire brush or a wire brush attachment for a hand drill.

Always make sure that the deposits are actually removed, rather than just burnished.

Clean the remaining cylinder head components in an engine cleaning solvent. Do not remove the protective coating from the valve springs.


WARNING
As most Mercedes-Benz cylinder heads are made out of aluminum, NEVER "hot tank" the cylinder head as is a common process with cast iron heads.

Place a straight-edge across the gasket surface of the cylinder head. Using feeler gauges, determine the clearance at the center of the straight-edge. If warpage exceeds .003 inch in a 6 inch span, or .006 inch over the total length the cylinder head will require resurfacing.

If warpage exceeds the manufacturer's tolerance for material removal, the cylinder head must be replaced.

Cylinder head resurfacing should be performed by a reputable machine shop in your area.

 
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