MTU M015710/04E Operating Instructions Manual page 121

7.2.2 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.
Findings
Minor dirt scores
Single scores
Scored area
Smoothened area
Bright area
Discoloration
Corrosion fields /
spots
Black lines
136 | Task Description | M015710/04E 2012-09
Action
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.
Clearly visible scores caused by hard particles. They usually start in the TDC
area and cross through the hone pattern in the direction of stroke.
Findings not critical.
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/ex‐
haust) along the transverse engine axis.
Findings not critical.
Smoothened areas are on the running surface but almost the whole honing pat‐
tern is still visible. Smoothened areas appear brighter and more brilliant than the
surrounding running surface.
Findings not critical.
Bright areas are on the running surface and show local removal of the honing
pattern. Grooves from honing process are not visible any more.
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 interrupted.
Findings not critical.
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 is corrosion pitting.
Black lines are a step towards heat discoloration. They are visible as a clear dis‐
coloration from TDC to BDC in the running surface and the start of localized
damage 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.