Inspection and restoration of pistons and piston rings (Mercedes-Benz E-Class W123)

1. If the pistons are being reinstalled on the engine, carefully remove the piston rings by spreading each one just enough to remove it through the bridge between the grooves on the piston body.

2. To prevent the rings from falling into the groove above, it is recommended to insert two or three narrow strips of tin (old feeler gauge plates) under the ring at equal distances from each other, and then twist the ring off the piston.

3. Clean the grooves and rings from carbon deposits so as not to scratch the aluminum surfaces of the piston.

4. If new rings are installed, the top compression ring must be stepped to avoid it hitting the "wear ring" that has formed at the top of the cylinder bore.

5. Before final installation of the rings on the pistons, measure the gaps in the ring joints. These gaps must comply with technical requirements.

6. Check the side clearance of the rings with a feeler gauge to ensure that it meets the specifications. If the clearance is too large, replace the piston, as its groove is worn along the height.

7. Install the rings and rotate their locks evenly around the piston circumference (by 120°).