Cylinder Head Removal and Replacement

Cylinder Head Removal and Replacement (in process as of 7/14/03)

Overview
My 1989 560 SEC with around 180,000 miles was been plagued with the typical puffs of smoke on start up. In an attempt to fix the problem, I replaced the valve stem seals a while ago, which cured the problem for a few months. While doing the seal I noticed that the #4 exhaust valve guide was loose, I could actually turn the guide.
Finally I decided, it was time to pull the head and have them reconditioned.
Note: When I say puffs of smoke on start up, that was basically to only time I would see smoke and I wasn't consuming much oil. I would add maybe 1 quart between oil changes (3-4k miles). If you are adding much more oil than that and see smoke while you're driving you're probably burning oil, which may suggest lower end (block) problems, which is not covered in this write up..

Disclaimer
My car is a 1989 US 560 SEC with a 117.968 engine. The procedures that follow apply to this vehicle and engine, I’m not sure how they may differ across other W126 vehicles and 117 engines. This write up is meant to be used as a reference only and not the actual procedure. Use the Mercedes 126 Engine Service Manual as the actual procedure. Also this is a very involved procedure and should only be attempted by individuals with advanced auto mechanical skills with all the necessary tools.

Other related Jobs.
Timing Chain replacement.
Upper Chain Guide Rails
Timing Chain Tensioner
Cooling System (hoses, radiator, thermostat, etc)
Brake Booster Vacuum Hose

Special Tools
Required:
Accurate torque wrench (10-120nm)
"U" body 8mm allen wrench
Box of sandwich size ziplock baggies & permanent marking pen.
MB V8 Valve spring compressor

Reference Info
Before and After Photos.

General Comments
Disassembly Note: This job involves removing hundreds items (parts, fasteners, etc). To make reassembly much easier, use sandwich size ziplock baggies and laundry mark to bag and label all associated components as they are removed. Replace fasteners that can be screwed back on the removed component. (i.e. removing the alternator, replace the electrical connection nuts on the studs and bag and label the mounting hardware) Also, it's a good idea to place a slip on paper in the bag with the component info. Motor oil will remove ink from a baggie.
Pay attention to, from where the screws/bolts are removed. Even though a bolt has the same thread size, if the length is too long, it could damage something when tightened. Read the manual closely, these kind of precautions are, in most cases, documented..

Procedure
Reference
MB Job 7.3-200 Removal and Installation of mixture control unit
I started by removing the air/fuel mixture unit. I disconnected the fuel lines into the fuel distributor, being careful to catch the fuel in a rag as I cracked open the connections. Disconnect and remove all the throttle linkages. Then remove all the lines to the fuel injectors. Remove the idle slide valve with rubber hoses. Unplug the connectors to both the EHA and throttle position sensor. remove the four 10mm nuts that mount the air/fuel mixture unit to the intake manifold. Loosen the clamp that secures the rubber air guide (bottom portion of the air/fuel mixture unit) and lift the air/fuel mixture unit off the throttle body (Fig-2).
That's the way it should come off, but the rubber air guide was so hard that I could not lift it off the throttle body. So I removed all the bolts around the perimeter of the air/fuel mixture unit and lifted off the top half. Then I was able to wiggle the lower half back and forth until I could lift it off (Fig-1).

Fig 1	Fig 2

Removing the Intake Manifold
Reference
MB Job 14-450 Removal and Installation of intake manifold upper & lower part, renewing gasket
I removed the all air distribution tubes, all the injectors, holders, o-rings and vacuum lines.. Remove the linkage brackets at the rear of the engine. Drain cooling system and remove left rear heater hose from the intake manifold and the thermostat housing top hose. Remove all the allen bolts that secure the manifold to the heads. Note that the 3 allen bolts in the center of the manifold secure the upper (Fig 2) and lower (Fig 3) sections.

Fig 3

With the intake manifold removed can see the head intake ports and the coolant passages. Note that below these ports there's a horizontal channel the runs from the front to the back of the head. This channel has a small hole into each exhaust chamber and is supposed to cool the exhaust as it was explained to me. As you can see in Fig-4 mine was totally packed with carbon. The guy whose reconditioning my heads (Bob) says he sees this a lot. See Fig 5-7..

Fig 4	Fig 5
Fig 6	Fig 7

Here's the lower section of the intake manifold (Fig 8)and these rubber rings seal the two halves. Mine were hard as rock and just loosely in place. Possible air leak and the cause for high idle which happens because air enters the system after the air flow meter. The oxygen sensor picks up in increase in the O2 level and orders more fuel from the EHA.

Fig 8

Removing Exhaust Manifold
Reference
MB Job 49-100 Removal and Installation of Exhaust System
MB Job 14-470 Removal and Installation of Exhaust Manifold
Removing the exhaust manifolds was a bit of a treat. Unfortunately, I didn't get any pix of this process, but it pretty straight forward. I started with removing the cross-member between the brake support mounts and the exhaust system. Then remove the left clamp the secures the left manifold and cross-over pipe (exhaust pipe that located between the engine and bulkhead). This clamp is accessed from under the car right behind the power steering. The clamp is secured be a single 11mm bolt with an attached nut on the backside of the clamp. This bolt will be rust covered, spray WD40 on the nut and allow to soak. Use a 6-point (to avoid rounding off the bolt head) 11mm socket and slowly work the bolt back and forth until the WD40 breaks the surface rust. If you rush this process the nut may start turning on the backside making it more difficult to remove this bolt. Once it breaks loose you'll be able to remove the bolt with your fingers. With the bolt out spread the clamp and remove. Repeat process for the right side. Access from under the car, directly above the front exhaust pipe flange. (The left side took me 5 minutes to remove, the right side took an hour because the nut started turning.)
Disconnect the EGR valve and piping from the left manifold. Remove the lower 4 manifold nuts, first soak with WD40. You will most likely back out the stud instead of just the nut, but that's okay. Then remove the upper 4 manifold bolts and wiggle the manifold loose of the cross-over pipe. Remove manifold from the top side. Repeat process for the right side manifold and remove from under the car.
Once I got the exhaust manifolds off, I found something very interesting. First, I could see where the oil was leaking down through the loose #4 exhaust valve guide. Second, the #2 exhaust port (Fig-9) was half clogged with a mineral deposit of some sort. Bob says he's never seen anything like this in the exhaust port, but has seen it in water passages when certain antifreezes react with the aluminum heads. He suggests sticking with manufacture's recommended antifreeze and changing coolant every year.

Fig 9

Removing the Cams
Reference
MB Job 05-220 Removal and Installation of Camshaft
MB Job 05-230 Removal and Installation of Rocker Arms
MB Job 05-310 Removal and Installation of Timing Chain Tensioner
MB Job 05-330 Removal and Installation of Tensioner Rail
MB Job 05-340 Removal and Installation of Slide Rails
Firewall: In order to get easier access to the rear head bolts, remove the top section of the outer firewall. This firewall (or bulkhead) is in three panels (left, center and right). On the right side, remove the window washer reservoir and battery. Detach the various electrical connection block from the firewall. Then remove the screw that secure the right panel to the top of the wheel well and to the center panel. On the left side, remove the brake booster vacuum line by loosing the 19mm coupling nut from the supply pipe (hold with 17mm wrench). Then loosen the 19mm coupling nut on the booster. With the line loose, push the rubber boot through the firewall into the engine compartment side and remove line. Again, disconnect any electrical block, vacuum lines and securing screws. Then carefully lift the panel out, making sure to leave the rubber feed-through grommets behind. Note: There are some plastic grommets that open up and stay on the panel.
Remove spark plugs.
Cam Oiler Pipe: Gently use a screwdriver to pry each of the plastic fitting off the cam bearings. They may break, but that's OK as you'll be replacing these pieces anyway. Just be sure to remove all the broken pieces. Also be careful to not bend the pipe.
Rocker Arms: Remove and place in 16 labeled baggies (i.e. #1-intake,#1-exhaust,#2-intake,etc), the rocker arms and tappet shim from each valve assy. These must be returned to their original position on reassembly. This job requires a special valve spring compressor tool. Be sure the piston is in the lower position and the cam lobe is point up when removing the rocker arm.
Caution: When manually turning over the engine, always turn the crankshaft in a clockwise direction.
Cam Timing: Turn engine over so that timing is positioned to Top Dead Center (TDC), that's the 0|0 mark on the harmonic balancer. The left and right cam timing marks should be very close to aligning. Note their exact position, either on paper or digital photo. Also mark the chain and sprocket on each side, so when you reassemble, you can easily line up these marks and then verify then timing marks are all line up as they were.
Caution: On reassembly these marks MUST line up near perfectly to they way they were or when the engine is turned over, you WILL experience catastrophic engine failure (i.e. pistons crashing into valves). I say "near perfectly" because when the heads are milled the cam timing will be off by a couple of degrees. Note that if the chain is off by one tooth on the sprocket, the cam timing will be off 18 degrees.
Timing Chain tensioner: Remove the two 13mm bolts and remove. Hold tensioner in place as bolts are being remove to keep it from cocking.
Sprockets: Use 7/8" hex socket to loosen the sprocket retaining bolt. Use a large adjustable crescent wrench to hold the cam from turning. In the center of the cam there's are two nubs that you can lock the crescent wrench to. Be careful to not drop any down into the timing chain galley when work over that area. With the sprocket bolt out, carefully rock the sprocket back and forth while pulling is forward. Watch that the woodruff key does fall out as the sprocket is removed. Bag and label parts.
Caution: Use a length of wire (coat hanger) to keep the chain from dropping down into the engine.
Tensioner rail: Remove per MB procedure.
Slide Rails: There are 3 upper plastic rails which have to be removed. See the MB procedure. The rails are secured by 2 pin each. These pins have to be pulled out of the heads. I made my own slide hammer by welding a (I think) 6mm bolt to a long rod and used a small sledge hammer head as the slide. The bolt and rod are screwed into the end of the pin and hammered out.

Removing the Heads
Reference
MB Job 01-415 Removal and Installation of Cylinder Head
MB Job 46-710 Removal and Installation of Power Steering Pump
MB Job 15-535 Removal and Installation of High Voltage Distributor
Remove the alternator and bracket.
Distributor: Remove the distributor, but first note the distributor body's position in the block. Simply loosen the retain bolt and lift the whole assy out.
Power Steering Pump: Remove the power steering pump from its bracket, but leave the hydraulic line connected. Then remove the p/s bracket plate, but before removing, note that there are 4 bolts that secure the bracket to the engine and there are 2 sets of 4 bolt holes. Remember which set of holes the bolts went through. If you use the wrong set, you either won't be able to get the belts back on or possibly won't be able to adjust the belts tight enough.
Hydraulic Compensating Elements: These are the 16 large ball headed bolts that the rocker arms rest on. Before the heads are sent to the machinist, it should be stripped down as much as possible (check with your machinist). So these elements should be removed and is easier done with the heads still mounted to the block. These elements are pumped up with oil and should be stored in an upright position when removed from the head. So take a cardboard box and punch 16 holes in the overturned bottom. Label each hole like the rocker arms and place each element in its respective hole.
Head Bolts: Loosen all the head bolt in the order explained in the MB procedure. These must be loosened in this specific order, so to reduce the possibility of head warping. I may be a little anal, but I labeled the position of each bolt so they could be returned to their original position. I simply punched holes (corresponding to the bolt position) in the bottom of a cardboard box and pushed the bolts into the appropriate hole. This made reassembly a little easier.
Lifting off Heads: The heads won't want to simply lift off and must be persuaded a little. I found a spot on the right head in the forward upper corner that I could pry the head loose of the block. The left side I use a rubber mallet to gently knock it in an upward direction to loosen it up.
Caution: Always be careful to not scratch or gouge the head or block mating surfaces.
Caution: With the heads removed, there are plenty of openings in the block for small tools, fasteners, dirt, etc to find their way into. So to avoid the drama of fishing a stray washer out of a water jacket, keep a piece of cardboard or something over the open block while not working on that area.

Fig 10	Fig 11

Rebuilding Cylinder Heads
This is a job that really can't be done by the average DIY'r. It's best to send your heads out to a reliable machinist. I asked the Parts Manager at my MB Dealership where they send their head work. In the So. Jersey area, I sent my heads to Anchor Atlantic in Pitman, NJ. Typically when high mileage heads (150K miles) go bad, the valve guides wear to where they loosen up in the head and the valve stem seals harden. One of the symptoms are puffs of smoke starting the car after it's been setting for a while. What happens is, as the car is setting, oil leaks down into the cylinder past the valve stem seam and/or down past the loose valve guide. Replacing the valve stem seals may fix the problem for a while, but bad valve are are not going to fix themselves. Also make sure you have the machinist fix any stripped or damaged spark plug holes.
Work that was done on my heads:
- The heads were sonic cleaned and bead blasted.
- Pressure tested for leaks.
- Valves were removed, springs tested, rotocups cleaned and checked, any parts would have been replaced if found defective, but all the parts looked good.
- Old valve guides were pressed out of the heads and new guides installed. In some cases the valves guides were loose in the head and special oversized guides were installed.
- All the old valves and seats were cleaned, reground on all three sides and lapped.
- The head's mating surface was damaged by head gasket failure. The aluminum in those areas was badly pitted. one area was so bad that had to be rewelded and milled. Other areas outside the fire ring were filled with JB weld.
- The valves were reinstalled in their original positions and new seals installed.
- Repaired (with heli-coil) a marginal spark plug hole and check the others.

Other Outside Work
In addition to the cylinder heads, I had Atlantic sonic clean my exhaust manifold and upper/lower intake manifolds. Bob at Atlantic told me it took several passes to get the inside of the lower intake clean. Then I sent the exhaust manifolds out to have them powder coated so they'd always look good.

Preassembly and Inspection
While the heads are out for reconditioning take the time to clean up the engine block and surrounding area. Again, be careful to not let a debris get into the exposed block openings. Be sure to very carefully clean the mating surface of the block of all remaining gasket material. Use a new utility razor to carefully scrape the old gasket off. Keep the blade as flat to the surface as possible to avoid nicking the the soft aluminum surface. Finish off the light remains with a drill mounted scotch bright pad. Do not use too must pressure because those pads can be quite aggressive and you'd end up damaging the block.
Inspect the cylinder walls for any heavy scratches or gouging. If the engine was maintained properly the cylinder wall should look almost flawless ( at least mine were, with about 180k on the clock). What ever slight scratches I could see, I couldn't feel them. If you do see and feel some significant scoring, I would suspect you would have had some significant oil usage.
Also clean up all the cylinder head bolt holes with Q-Tips and compressed air. Make sure the threads are clean and free of any gunk. Make sure all the bolts are cleanup too. I let the bolts soak in kerosene and used a brass wire brush to clean the threads up.
Use a wet vac to clean any debris from the cylinders, water jackets, etc.

After everything is cleaned up and the heads have come back from the machinist, take the time to carefully run the spark plugs and exhaust bolts/studs into each hole while the head is on the bench. It just makes it easier to clean out, if some debris found it way into the threads while it's on the bench rather than back on the engine.  Don't leave the exhaust manifold studs in, it's easier to install the manifold with the studs out.
Use a good flashlight to carefully inspect all the head ports and passages, use an air hose (or shop vac) and give all these crevasses the once over to clean any of the machinist debris that may have been missed. It's always better to save than sorry, if some metal filing were left behind, they could do some damage if they find their way past the oil filter.
Note: A good machinist would protect his work (and your heads) by carefully cleaning and wrapping the heads in plastic to keep debris out while the heads are in transit and awaiting installation.

Installing the Heads
Reference
MB Job 01-415 Removal and Installation of Cylinder Head
Install head gaskets as described in the MB job. Carefully have someone feed the timing chain through the chain galley as you gently place the head on the guide pins on the block. Make sure the the head is squarely seated and place the upper most head bolts in the head and finger tighten to hold the head in place. Carefully mount the cam and cam bearings installing the appropriate bolts.
Note: Only finger tighten the bolts, must must follow the MB procedure for torquing the heads bolt to avoid damaging the head and/or leaks.

Timing Chain Guide Rails: Install upper timing chain guide rails
Timing Chain Tension: Install the tensioner guide rail. wait to install the tensioner until after the sprockets are installed.
Cam Sprockets: Install the two sprockets aligning marks that you applies before disassembly. Note that you must ensure that the cam timing in set correctly before installing the rocker arms. With all the rocker are out, you can turn the engine over (manually) without the fear of damaging the valve (and pistons) it the timing is not set correctly.
Timing Chain Tensioner: Install the timing chain tensioner and verify that the cam timing is correct. If the timing is off, remove the tensioner, remove the sprocket and rotate the sprocket the direction to bring the timing marking in line. When the timing is set correctly, torque the tensioner. Note: It's normal for the right cam timing to be off a little (less then 18 degrees), if the head had to be milled, because the head is setting lower slacking the chain slightly. Which cause the the valve timing to be a little later.