Checking pistons and connecting rods (Mercedes-Benz S-Class W126)

Clean and inspect all parts. If any parts show signs of chipping, scratching or wear, they must be replaced with new ones. The piston pin seating locations must be selected so that the pin can easily move in the connecting rod at room temperature. The piston pins of individual cylinders must not be replaced.



Measure the clearance by the height of the piston rings in the piston grooves, then insert the piston rings in order into the corresponding grooves.



Insert the rings one by one into the cylinder hole.

Using the removed piston, move the ring down approximately 20 mm. Now it sits in the hole precisely.

Insert a flat feeler gauge into the gap between the two ends of the ring to measure the gap in the ring lock. When replacing only the piston rings, this gap should be measured at the lower end of the hole, since in this position it is the smallest.



Connecting rods that are used again must be checked for bending and distortion. A connecting rod that has overheated due to bearing damage (it turns blue) must not be reused. Connecting rods with a machined connecting rod bushing are supplied as spare parts. The connecting rod bolt hole must also be checked. To do this, place the connecting rod cap on the connecting rod bolts. If the cap moves downwards under its own weight, the connecting rod must be replaced. When assembling pistons and connecting rods, pay attention to the following:



Mark the relative positions of the connecting rods and connecting rod bearing caps with a center punch (1 point - 1st cylinder, etc.). The crank pin must not have any transverse scratches or nicks.

Lubricate the piston pins and piston holes before pressing in.

The ends (locks) of the piston rings should be placed evenly around the circumference of the piston.

Install the pistons on the connecting rods so that the arrow points in the direction of travel.