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Task Description
6.2.2
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 examination report.
Minor dirt scores
Single scores
Scored area
Smoothened area
Polished area
Discoloration
Corrosion fields / spots
Black lines
Discolorations (Heat)
Seizures, Seizure marks
MS15009/00E 06-09
Light scoring can take place during the assembly of a new engine (honing products,
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 from 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/exhaust)
along the transverse engine axis.
Findings not critical.
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 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 temperature
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 are corrosion pittings.
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.
These are caused by a disturbance in the liner / ring tribosystem. Usually they run
over the whole ring-travel area (TDC/BDC), starting at the first TDC-ring and becoming
more visible from the second TDC-ring onwards and less pronounced from TDC-ring
1. The honing pattern is usually no longer visible and displays a clearly defined
(straight) edge to the undisturbed surface. The damaged surface is usually discolored.
The circumferential length varies.
Liners with heat discoloration starting in the TDC-ring 1 have to be replaced.
Irregular circumference lengths and depths. Can be caused by either the piston skirt
or the piston crown. Material deposits on the liner (smear), heavy discoloration.
Severe, visible scoring.
Replace liner.
93
© MTU
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