Attention! Attention! Replace spark plugs only when the engine is cold or slightly warm. If the spark plugs are removed on a hot engine, the threads of the light metal cylinder head may be damaged.
Before starting work, prepare all the necessary tools. Some spark plug manufacturers supply special tools to measure the spark plug gap.
Engines 111, 271
- Candle wrench 16 mm, e.g. HAZET-2506 or -2776 (engines 111, 271) or HAZET-4766 (engine 112).
- Additionally, it is recommended to purchase special pliers, for example, HAZET 1849, which make it easier to unscrew the candles. MERCEDES-BENZ uses the 3277A assembly key for this.
- Depending on the number of engine cylinders, the required number of spark plugs. Applicable spark plugs are listed in the Specifications.
Remove spark plugs.
1 - Candle key
2 - Candle shaft
3 - Ignition coil
1. The best way to replace spark plugs is to buy new spark plugs in advance, adjust their gap, and replace each spark plug in turn. When buying candles, it is very important to choose exactly those candles that are designed for the engine of your car. Information about them is given in the Specifications.
2. With new spark plugs on hand, let the engine cool completely before removing the old ones. During this time, you can inspect new spark plugs for defects and check spark plug gaps.
Attention! Do not touch high voltage parts. Persons with a pacemaker should not carry out any work on the electronic ignition system.
3. Remove the ignition coils, refer to Section Removal and installation of ignition coils.
4. Remove the spark plugs with a spark plug wrench (1). When doing this, make sure that the key is straight and not skewed.
Examination
1. Compare the removed candle with those shown in the pictures in the Chapter Engine electrical equipment, this will give you useful information about the general condition of the engine.
2. Check the electrode spacing with a probe. The required gap value is given in the Specifications.
Note. With new spark plugs, the electrode spacing is usually set correctly.
3. To set the distance between the contacts, bend the corresponding ground electrode. To do this, tap on the side of it. When bending, rest a small screwdriver on the edge of the thread. Never lean on the center electrode as this can be damaged.
4. Apply a small amount of copper anti-seize compound to the threads of the new spark plug. Install the spark plug in the cylinder head and screw it in with your fingers until it stops, then tighten it with the head of the spark plug wrench. If possible, use a torque wrench to tighten the spark plug to make sure it is installed correctly. Plug tightening torque is included in Specifications.
Recommendations: To avoid the possibility of screwing the spark plug out of thread, put a small piece of rubber hose or plastic tube on its shank. The flexible tube will work as a universal joint, ensuring that the spark plug is aligned with the spark plug socket, and if the spark plug starts to warp, the hose will slip on it, making it impossible to strip the threads.
5. Before connecting to a high-voltage spark plug (BB) wire, carefully inspect it for damage, corrosion of the internal contact and measure the resistance. If it significantly exceeds 30 kOhm / meter, replace the entire set of wires.
6. Connect the wire to the installed new spark plug, again using a twisting motion and holding the connector until it is fully seated on the spark plug.
7. Repeat the above procedure for the remaining spark plugs in sequence to avoid incorrectly connecting the spark plug wires.
Installation
1. Insert the spark plug and screw it all the way into the cylinder head. After that tighten a candle the moment specified in Specifications. At the same time, the candle key (1) keep straight (A), without twisting it (IN).
2. Install the ignition coils, refer to Section Removal and installation of ignition coils.
Repairing damaged spark plug threads
If the spark plug thread in the cylinder head is found to be damaged, it must be repaired. Suitable tools and repair kits are available for this, for example from BERU. The damaged thread is drilled out with a special drill. It is not necessary to remove the cylinder head to do this. Then a new thread is cut in the head and the candle is screwed into a special adapter threaded insert. The additionally installed threaded inserts of the candles sit firmly and ensure tightness.
Engine 112
Only differences from 4-cylinder engines 111, 271 are described.
Removing
Twin ignition coils for two spark plugs a and b of one cylinder
1 - Coil housing a and b
2 - Designation on the valve cover
1. Remove the cover from the end of the motor.
2. Remove the upper part of the air filter housing (only for engines with an air filter located on the side of the vehicle).
3. Remove the air mass meter with suction pipe (only for engines with an air filter located on the side of the vehicle).
4. Remove the engine cover or air filter, refer to Section Removal and installation of the air filter.
5. Disconnect ignition coils (1).
6. Disconnect the spark plug plug using a double spark plug wrench above the cylinder head cover.
7. Turn out spark plugs.
Installation
1. Screw the candles by hand until it stops into the cylinder head and then tighten with a torque of 28Nm.
Attention! Each cylinder has two spark plugs. In order not to confuse the plugs, it is necessary to mark them in the same way as the cover on the engine (2).
2. Connect the plugs to the candles.
3. Install the ignition coils and secure with a torque of 8Nm.
4. Install the engine cover or air filter, refer to Section Removal and installation of the air filter.
5. Install an air mass meter with spigot (only for engines with an air filter located on the side of the vehicle).
6. Install the upper part of the air filter housing (only for engines with an air filter located on the side of the vehicle).
7. Attach the cover to the end of the motor.