7.3.2 Instructions and comments on endoscopic and visual examination of cylinder
liners
Terms used for endoscopic examination
Use the terms listed below to describe the condition of the cylinder-liner surface in the endoscopic exami‐
nation report.
Finding Action
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
fingernail.
Findings not critical.
Single scores Clearly visible scores from hard particles. They usually start in the TDC area
and cross through the hone pattern in the direction of stroke.
Findings not critical.
Scored area These areas consist of scores of different length and depth next to one anoth‐
er. In most cases, they are found at the 6-o'clock and 12-o'clock positions (in‐
let/exhaust) along the transverse engine axis.
Findings not critical.
Smoothened area Smoothened areas are on the running surface but almost the whole honing
pattern is still visible. Smoothened areas appear brighter and more brilliant
than the surrounding running surface.
Findings not critical.
Polished area Polished areas are on the running surface and show local removal of the hon‐
ing pattern. Grooves from honing process are not visible any more.
Discoloration This is caused by oxidation (surface discoloration through oil or fuel) and tem‐
perature 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 interrupt‐
ed.
Findings not critical.
Corrosion fields / spots Corrosion fields / spots result from water (condensed water) with the valves in
the overlap (open) position. They are clearly visible due to the dark color of the
honing groove bottom.
This corrosion is not critical unless there are corrosion pittings.
Black lines Black lines are a step towards heat discoloration. They are visible as a clear
discoloration from TDC to BDC in the running surface and the start of localized
damage to the honing pattern.
Cylinders with a number of black lines around the running surface have limited
service life and should be replaced.
76 | Task Description | M015650/03E 2011-10
TIM-ID: 0000000014 - 009
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