Replacing the head gasket in a Mercedes can be a very difficult and time-consuming process. However, with the right tools, knowledge and patience, it can be done. Accessing the head gasket requires that you remove many components of your engine and disconnect many valves and wires. The basic idea is to remove anything blocking access to the gasket, and this may differ depending on your specific Mercedes.
Open the bonnet. Disconnect the negative battery terminal to prevent electrical shock. You can disconnect the cable by finding the negative terminal, and using a socket wrench to turn the bolt on the terminal connector counterclockwise.
Remove the header, intake and exhaust unit. The removal process will vary based on the model and year of Mercedes. The header is generally bolted on, but it may need to be cut off with a welding torch depending on the age. the intake can be generally removed with a screwdriver by unscrewing the bracket holding it on. The exhaust will have to be cut off with a welding torch.
Remove the plastic insignia plate covering your valve cover, if one exists. Remove it by prying it off with your hands or a screwdriver. Plastic insignia plates are generally held on by clips and can be removed by hand. Pull carefully as to not break any clips.
Remove each bolt securing the valve cover by turning counterclockwise with a socket wrench.
Slide off the valve cover.
Flip over the valve cover to view the gaskets.
Remove the gaskets from the valve cover by peeling them off. You may need to scrape the remains off with a flathead screwdriver.
Inspect the groove that the gaskets sit in to assure that there is no warping or cracks.
Use any automobile cleaner to clean the inside of the valve cover.
Place the new gaskets into the valve cover ensuring that they fit in exactly.
Place some RTV silicone on each corner of the cam journals to ensure a tight and secure fit. The cam journals are merely the openings to the cam. They are circular in shape, and they are the first thing you'll see when you remove the valve cover.
Position the valve cover back in place.
Reattach the bolts to secure the valve cover using the correct torque technique. The centre bolt is first working side-to-side and outwards.This will insure that the cover sits uniformly.
Reattach and reconnect any parts or lines you removed to provide access to the valve cover. The parts removed will vary based on the year and model of your Mercedes. Most Mercedes don't require you to remove anything to get to the valve cover -- other than the plastic insignia plate -- so you won't have anything that you need to reconnect.
Press the plastic insignia plate back into place with firm pressure until you hear the clips lock into place.
Reconnect the negative terminal of your battery.
Test your engine to ensure that it is running properly.
Step 2 outlines removing items that are most likely covering your valve cover. These may differ based on your specific Mercedes model. However, the ultimate goal is to remove all lines and parts interfering with access to the valve.