MTU 12V 2000 G23, Use And Maintenance Manual

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6 – 06 Cylinder Liner
6.2.2 Instructions and comments on endoscopic and visual
examination of cylinder liner
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 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.
Single scores Clearly visible scores from hard particles. They usually start in the TDC area and cross
through the hone pattern in the stroke direction.
Findings not critical.
Scored area These areas consist of scorings next to one another of different length and depth. 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 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 honing
pattern. Grooves from honing process are not visible any more.
Discoloration 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 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 to 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.
Discolorations (Heat) 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 towards the second TDC-ring . The honing pattern is usually not visible
any more and has 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.
Corrosion Corrosion traces have irregular circumferential length and depth. They can be caused
by either the piston skirt or crown. The material deposit on the liner (smear) shows
heavy discoloration and heavy scoring.
Replace liner.
M015560 / 00E 03-05 © MTU