Engine - Determining Cylinder Wall Condition

REF. NO. 01/30
TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: May 1994

SUBJECT:
ENGINES 116.96/117.96, 119, AND 120
EVALUATING ALUMINUM BLOCK CYLINDER WALLS

When an engine is examined for complaints of noise, overheating, oil consumption, etc., the cylinder walls should first be examined using a borescope with the cylinder head(s) installed.

The following guidelines are intended to help determine the condition of the engine block and its suitability for further use. If this cannot be determined adequately using the borescope, the cylinder head(s) must be removed.

1. Normal condition
Matte grey surface. no hone marks.





2. Smooth or shiny worn areas (Figure 1)
Isolated polished areas, for example, in the middle of the cylinder or in the area of the cylinder head bolt bores.
Engine block can be used further.

3. Smooth, shiny, polished surface around most of cylinder wall (Figure 2)
Usually beginning at the first piston ring, in the upper end of the cylinder with measurable partial cylinder wear.
Cylinder wall not suitable for further use.





4. Visible lines, scuff marks (Figure 3)
Beginning at first piston ring, ending after approx. 30 mm. Scuff marks, which cannot be felt, caused by fuel washing away oil film, such as in frequent cold starts in short distance driving.
These scuff marks which occur primarily in the area of the cylinder head bolts and on the thrust side are not a concern as long as they are healed. The piston rings are not damaged. Engine block can be used further.

5. Roughened lines, scoring (Figure 4)
Beginning at the first and second piston ring, ending only at the lower end of the cylinder. Scuff marks as described in 4 progressing into score marks. Piston rings may be damaged.
If marks can be felt, cylinder wall not suitable for further use.

6. Isolated continuous scratch marks
Caused by contaminants such as the reversion of carbon particles from the exhaust. Engine block can be used further.

7. Ring shaped impressions (Figure 1)
Visible in the upper and lower area where the piston ring stops before reversing direction.
Engine block can be used further.

8. Piston seizing
Cylinder wall is usually roughened over the entire length. Material transfer and noticeable scoring that can be felt on the cylinder wall and piston skirt.
Cylinder wall not suitable for further use.

9. Brown discoloration of cylinder surface
This discoloration over large areas is oil varnish indicating that the engine was operated at high temperature levels.
Engine block can be used further provided that no unacceptable cylinder distortion is found. Oil varnish above the piston ring area is normal.