General information on inspecting cylinder walls - AH01.00-P-0300-01AK

ENGINE 266.920/940/960/980 in MODEL 169.0/3, 245.2 

Pressure gloss marks, smoothing 

Individual blank areas in the middle of the cylinder barrel or in the area of the cylinder head bolts.

The crankcase can be reused.

Fig 1: Identifying Cylinder Barrel Pressure Gloss Marks

Courtesy of MERCEDES-BENZ USA

Visible stripes, friction marks 

Starting from the reverse area of the upper piston ring tapering down. Traces of dry rubbing which cannot be felt, caused by oil film being washed off by fuel, for example during frequent cold starts during short-distance driving.

Friction marks occurring mainly around the cylinder head bolts and on the pressure side are not a problem provided that they are smoothed out.

The piston rings are not damaged.

The crankcase can be reused.

Fig 2: Identifying Cylinder Barrel Visible Stripes (Friction Marks)

Courtesy of MERCEDES-BENZ USA

Ring shaped imprints 

Visible imprints on cylinder barrel in the upper and lower reverse area of piston rings are not a cause for complaint.

The crankcase can be reused.

Fig 3: Identifying Visible Imprints On Cylinder Barrel

Courtesy of MERCEDES-BENZ USA

Rotary bright, reflective, polished upper surfaces of cylinder 

Starting from the reverse area of the upper piston ring with measurable, partial cylinder wear.

The cylinder barrel is unusable.

Fig 4: Identifying Polished Upper Surfaces Of Cylinder

Courtesy of MERCEDES-BENZ USA

Roughened mottling, friction scoring 

Starting from the turnaround point for the upper piston rings and then running in the lower part of the cylinder.

Friction marks as described under "Visible stripes, friction marks" can lead to rubbing erosion.

Where these signs of friction are perceptible, the cylinder barrel is unusable.

The piston rings may be damaged.

Fig 5: Identifying Roughened Mottling (Friction Scoring)

Courtesy of MERCEDES-BENZ USA

Continuous individual traces of scratching 

Caused by soiling, for example, by the back-pulsation of soot particles from the catalytic converter or exhaust.

The crankcase can be reused.

Piston seizure 

Most of cylinder wall perceptibly roughened over the entire length.

Material deposits and perceptible scoring marks on cylinder wall and at piston skirt.

The cylinder barrel is unusable.

Brown coloring of cylinder upper surface 

Oil varnish over larger areas of the cylinder barrel signalize that the engine has been run at a high temperature.

The crankcase can be reused if no impermissible cylinder warping is visible.

Oil varnish above the piston ring zone is normal and should not be considered a cause for complaint.