8.2.2 Cylinder liner – Instructions and comments on endoscopic and visual
examination
Terms used for endoscopic examination
Use the terms listed below to describe the condition of the cylinder-liner surface in the endoscopic examina-
tion report.
Findings Measure
Minor dirt scores Minor dirt scores can occur during the assembly of a new engine (honing prod-
ucts, particles, broken-off burrs). Removed cylinders clearly show such scoring on
the running surface under endoscope magnification. Cannot be felt with the fin-
gernail.
Findings not critical
Single scores Clearly visible scores caused by hard particles. They usually start in the TDC area
and cross through the honing pattern in the direction of stroke.
Findings not critical
Scored area These areas consist of scores of different length and depth next to one another.
In most cases, they are found at the 6-o'clock and 12-o'clock positions (inlet/
exhaust) along the transverse engine axis.
Findings not critical
Polished area Polished areas are on the running surface but almost the whole honing pattern is
still visible. Polished areas appear brighter and more shiny than the surrounding
running surface.
Findings not critical
Bright area Bright areas are on the running surface and show local removal of the honing pat-
tern. Grooves from the honing process are not visible any more.
New cylinder liners must be fitted in the following cases
Polished area:
covers more than 20% of the entire piston running surface,
covers more than 30° of the circumference and extends over more than 50% of
piston stroke,
is wider than 15 mm over the entire piston stroke.
Discoloration This is caused by oxidation (surface discoloration through oil or fuel) and temper-
ature differences around the liner. It appears rather darker within the honed
structure in contrast to the bright metallic running surface. The honing pattern is
undisturbed. Discolorations extend in stroke direction and may be interrupted.
Findings not critical
Corrosion fields / spots Corrosion fields / spots result from moisture (condensate) with the valves in the
overlap (open) position. They are clearly visible due to the dark color of the hon-
ing groove bottom.
This corrosion is not critical unless there is corrosion pitting.
Black lines Black lines are a preliminary stage of burn marks. They are visible as a clear dis-
coloration from TDC to BDC in the running surface and the start of localized dam-
age to the honing pattern.
Cylinder liners with a large number of black lines around the running surface have
limited service life and should be replaced.
MS150049/04E 2017-04 | Cylinder Liner | 79
TIM-ID: 0000003285 - 004
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