Engine and Timing Marks — Basic Information and Use (Mercedes-Benz C-Class W201)

1. Top dead center (TDC) is the highest point in the cylinder that each piston reaches during its crankshaft rotation. Each piston reaches TDC at the end of the compression stroke and again at the end of the exhaust stroke. However, TDC generally refers to the position of the piston during the compression stroke. Piston #1 is located on the camshaft timing chain side.

2. Setting the piston of the 1st cylinder to the TDC position is an important condition for many procedures, such as replacing the drive chain and replacing the camshaft.

3. Locate the high-tension wire terminal of cylinder 1 on the distributor cap. If the terminal is not marked, trace the high-tension wire from the spark plug of cylinder 1 to the cap (cylinder No.1 is located on the engine side of the drive chain).

4. Remove the camshaft cover as described in paragraph 4.

5. Using a suitable wrench socket on the vibration damper hub bolt/crankshaft pulley, turn the crankshaft clockwise until the following marks are aligned (see Fig. 3.5, a, b).

• a) The TDC ("O/V") mark on the crankshaft pulley is aligned with the indicator on the camshaft drive chain housing.
• b) The TDC notch on the flange in front of the camshaft is aligned with the upper surface of the cylinder head.
• c) The distributor rotor is aligned with the mark on the outer rim of the distributor housing (you may have to remove the mudguard to see the mark).

6. When the marks are aligned as described in step 5, the piston of cylinder 1 will be at TDC. If the camshaft timing chain is removed, do not turn the crankshaft until the chain is reinstalled.

[Original published on the website mercedesman]