Mercedes Repair/Maintainance Transmission, etc... Tips
Found the followng Mercedes repair article and thought many of you will be interested in reading it too. It contains some useful transmission tips on the W163.. There is a limit of 15,000 characters, so I will break this article in three sections/parts..
Mercedes Repair/Maintainance Tips
Recommended service intervals:
M104 every 45,000 mi or 4 years
M111 every 45,000 mi or 4 years
M119, M120 every 60,000 mi or 4years
M156, M275 every 60,000 mi or 5years
M112, M113 motors every 100,000 mi or 5 years
M272, M273 motors every 91,000 mi or 5 years
Some years have slightly different intervals, your owner’s manual will have the best information. Or call us and we will confirm it.
It helps to lubricate the threads with anti-seize as you don't want to gall the spark plug bores on removal or installation. You can also use light oil if you prefer but anti-seize is a better thermal conductor and is preferable in the interface. Galling occurs when the aluminum cylinder head threads seize and stick to the plated steel spark plug threads. Many spark plug manufacturers specify installing plugs dry as the anti-seize can increase the torque and cause thread damage. This is probably not the case but you should decrease the torque to compensate if desired, approx 20%. Just be careful the anti-seize doesn't get on the electrode as it is contains metal particles and is conductive and the spark will find the lowest resistance path to ground. Avoid the use of air tools until you are sure the spark plug is moving freely, and use a torque wench to finally install. The correct torque is important as it controls the rate of heat transfer, too loose and the plug will run too hot. A hot plug can cause pre-ignition, this occurs when the fuel air mixture ignites before the optimum piston position. This can cause peak cylinder pressures to occur before the piston is at TDC and if this occurs over time the engine pistons can be eroded and damaged. If the plug is too tight the threads may be damaged and hard to remove later. If the plug cannot be inserted and tightened all the way finger tight the threads may need to be chased with a thread chaser. This has to be done carefully lubricate with penetrating oil if you are cutting carbon, and grease the recesses in the tap if you are removing metal it will catch the shavings from falling into the cylinders. Fortunately, overheating plugs and galled threads are extremely rare on a Mercedes if you follow the tips in this section.
Replacing plugs on the M112 and M113 engines is much easier with the special tool to remove the wires without damaging them. This 17mm wrench was designed to adjust valves back before hydraulic lifters were common, this tool is now more commonly used as a spark wire removal tool. It gives you the proper fork like opening and leverage to make an difficult removal job easy. Hose pliers and boot removal tools are other less preferable options but do work. The correct tool is 110 589 01 01 00 if you do these a lot you may want to order one. Reproductions of this tool are available but the original design is open on both ends and twists in different directions, it helps when doing the back cylinders. Some copies I have seen are not quite the same, they may work well, but I haven't tried them. You may also want a spark plug installer it's all rubber tool that allows you to insert and and finger tighten plugs, cross threading is not something you want on a back cylinder where you have barely enough room for a hand. There are many different deigns the all rubber one from Mac tools works well. Be aware the most common source of ignition problems on these two engines are the spark plug wires. At the dealer the price of one spark plug wire is over $50 when you have 16 on a M113 it gets expensive quickly, may times to accommodate a budget only a few cylinders are done at a time. Iterating repairs and diagnosis time can get even more expensive. We can sell an OEM wire set for a M113 for around $400 while our labor to install is also substantially less than the dealer. Replacement of spark plug wires isn't that common but if you need to do several cylinders consider doing a set. The labor to replace the plugs and the wires is substantially less than doing them separately so if your dealer is using menu pricing make sure you ask for them to adjust for the labor overlap.
One other issue on The M112 and M113 engine is that the oil baffles at the top of the valve covers seep oil, changing the valve cover gaskets alone won't stop the oil seep. The reason it appears in this section is that if usually occurs after 5 years on on most of these vehicles the plugs also need to be replaced. If you can replace the plugs and reseal the valve covers the labor is reduced substantially. The seep when it gets bad covers he coils and wires in oil and dirt and although it can be cleaned up its something that can be avoided if you inspect the valve covers for the need or resealing at the same the plugs are replaced. The oil baffles on the valve covers are resealed with engine sealant 003 989 98 20 10, its the RTV type sealant that is used for most Mercedes engine assemblies that have no gaskets. This is an outstanding sealant that forms a very strong bond when fully cured, has a 10min work time and skins over quickly so it can be put into service within 30min. It takes awhile to fully cure but that is unimportant to its sealing qualities. Be aware it is critical that the surfaces to be bonded be cleaned of all old adhesive and dirt or any oil. Any oil and the finished assembly will leak. It is a labor intensive repair but it doesn't have to cost $1000. I recently resealed two valve covers both baffles and replaced the plugs on a CLK 430 and the total repair was approximately $800, the dealer estimate was $925 just for the valve cover gaskets. You could pay as much as $925 and would be amazed that in many cases the valve covers go in the spray cabinet washer the gaskets get replaced an the baffles are never touched. Technically, the oil baffle reseal is not part of the valve cover gasket operation so it may not always be done. It is an additional operation and is the most time consuming part of the job if done correctly. If you are in need of this repair make sure you do both the baffle and the gasket reseal, and if you are near 5 years or 100k miles do the plugs also. The labor overlap is considerable so its not unreasonable to ask if this was considered when preparing the estimate. At Foreign MotorWorks you can be sure all labor overlaps will be considered when preparing any estimate, so you don't double pay labor charges. For example if I need to remove the coils to remove valve covers or the plugs and I am doing both the total labor needs to be reduced to reflect the reality that the coils were only removed once, it is common for the labor amounts to be summed and no overlap considered.
A note on plugs in older engines before 1990, it is not uncommon to find the incorrect spark plugs in vehicles with distributor type ignition systems. If you plan upgrade sparkplugs you need to carefully inspect or replace all the secondary electronic parts or the end result may be carbon tracking, current leakage and misfiring. It is not practical or beneficial in many cases to do this. Use the OEM plug recommended for the motor. Some high energy plugs may last longer, but often have larger gaps and need more voltage to fire. If your coil cannot provide this voltage or the spark plug wiring insulation is poor, that voltage will find another path to ground. As a result the car won’t idle smoothly, making them a poor choice in this case. With sparkplugs only use the OEM parts or the results may be less than desirable even if the plugs are made of superior materials. Beyond issues of gap are subtle variations of heat range and resistance that make the choice of the correct spark plug best left the design engineer. It's best to keep to the OEM recommendations, there is little evidence to suggest that changing spark pugs from the OEM specification would have any benefits.
Use caution when replacing plugs on Mercedes motors produced between 1991-1196 as the insulation on the engine wiring harness can be brittle. On a M104 engine this is very common but may of these have already been repaired by replacing the engine harness. Check the insulation on any of the exposed wires in the engine harness, on the engine. The heat causes the insulation to crack and flake off, this may be visible. If the insulation is cracked don't touch anything unless you are committed to replacing at engine wiring harness because it may not start after replacing the plugs, or may misfire or backfire into the intake which can damage the throttle valve.
A common cause for misfires is a no spark or weak spark condition. For anyone interested in diagnosing a weak spark condition consider this. In a vacuum the voltage required to jump a gap is high, but the voltage drops with increasing pressure reaches a minimum and sharply increases again. This is called a Paschen’s law. If you use an ordinary spark plug to diagnose a no-spark condition you may mistakenly think the spark is normal and present, but when in the high pressure environment of an engine cylinder the spark may be absent. Use a high energy spark tester, these have very large gaps to compensate for the decrease in the needed voltage at atmospheric pressure. The reason for this is that in a high vacuum ionization of a gas cannot assist spark generation, gas presence is sparse in a vacuum therefore this ionized conductor not being present results in higher energy sparks. At high pressure ionization of a gas in inhibited by electrostatic forces caused by crowding of the ions in the gap, that’s why at lower pressures like atmospheric where an ionizable medium air is present but its concentration is still small that a minimum spark energy occurs. With this mind it also helps to explain why some misfires only occur under load, this is where cylinder pressures are highest and the needed spark energy is also the highest. Weak plug wires may not show up at idle but may turn on the CEL under hard acceleration. A high energy spark tester simulates the higher load condition where the misfire occurs. Most OBD II code scanners can also be helpful locating the problem cylinder if the vehicle was built after 1997. Beyond this ignition scopes provide the best window into cylinder ignition condition and compression, but they are seldom needed on OBD II vehicles because the on board testing is so comprehensive. Misfire recognition is very sensitive, and in case where a leaking valve may be suspected a relative compression check can be performed electronically on some engines with a scan tool which can monitor starter draw current. The relative current draw for a leaking cylinder will be low, this in many cases is much faster than a conventional compression check which can be performed after if needed. If the problem can be uncovered quickly with the correct equipment the corresponding diagnosis cost to you will be the lowest. If you are doing the repairs yourself or at a shop without diagnostic technicians consider the cost of replacing unneeded components, it may be better to have it professionally diagnosed by a specialist before replacing any parts. You can then choose to repair it yourself if desired.
Modern timing chains can be expected to last the life of the engines but some engines such as the M119 have reported failures, bent valves, mostly due to plastic guide failure although this is uncommon if you have any abnormal engines noise you should have it checked. Broken oil tubes on the M119 can also cause loud lifter noise. If your engine has more than 150,000 miles on it and you have done all the scheduled maintenance chances are the timing chain is fine. If it's an older engine from the 1970's or 1980's or has a single roller chain it may be needed. The bottom line is the only way to know for sure is to check it, if it’s fine leave it alone. It would be rare to break without wearing out first. To check it, with the valve covers off rotate the engine at the crank bolt manually clockwise to TDC, either the cam timing marks line up or they don’t. Don’t rotate counterclockwise if you miss TDC, that’s when plastic rails snap. Regardless, you need to take up the chain slack to get a valid measurement so always only rotate in the direction of normal engine rotation.
If the timing marks don’t line up you have chain stretch, installing an offset woodruff is one solution for small corrections, but for anything more than a several degrees you are inviting disaster. On an interference engine loss of the chain is loss of the engine in many cases, unless it occurs at low engine speeds even then valves will be bent on several cylinders. If you replace the chain check the sprockets if blunted or rounded they should also be replaced, a worn sprocket will quickly wear out a new chain. Consider chain and sprocket wear fitted parts. If they are worn replace them both. Realize that the labor to pull the front cover and replace all the sprockets is considerably more than feeding a new chain in, but it won’t last long if your sprockets are worn. For do a chain if its needed unless then make sure its done correctly or it will need to be done again.
If you remove the timing chain you removed the chain tensioner, don't forget to reset it is the ratcheting hydraulic type or you may end up with a chain that's far too tight. You'll hear the chain noise if you missed this step and risk snapping a camshaft or braking the chain if driven like that. You need to dismantle the chain tensioner, to do this remove the allen nut then the spring and spacer. Pull the pin out fully, it only goes one way. Then insert the pin in through the back so it not extended. Install the tensioner with the 27mm nut and the allen nut installed, the chain should be properly installed and timed. Then insert the spring and spacer, compress the spring and install the allen nut. Replace the aluminum seals if they look at all compressed or damaged. Installing the allen nut while compressing the spring is most easily done with an air ratchet, if you use air tools to start the job make sure to finish with a torque wrench.
2005 ML 500
Black, 18" AMG Wheels, 285/60R18 Yokohama Geolander HTS + Bi-Xenons(+ Drew's e-code mod, though the reflectors rusted off and do not give out much light anymore), Yakima roof bars, Akebono pads all around. Former vehicle 2001 ML 320 with 108K miles, when traded, and a large repair/defect history. After all these years of owning my current 2005 ML 500, it is a major unreliable vehicle with a very large/expensive repair/defect history and has been like this since brand new.
Last edited by AC_ML; 08-21-2009 at 10:20 AM.