96 Task Description
6.2 Cylinder Liner
6.2.1 Cylinder liner Endoscopic examination
Preconditions
Engine is stopped and starting disabled.
Special tools
Designation / Use Part No. Qty.
Rigid endoscope Y20097353 1
Preparatory steps
1. Remove cylinder-head cover ( Page 105).
2. Remove injector ( Page 107).
Positioning crankshaft at BDC
1. Using barring device, turn crankshaft until crankpin of the cylinder to be tested has reached BDC.
2. Insert endoscope into cylinder liner through injector seat.
Cylinder liner - Endoscopic examination
Findings Task
Thin carbon coating on carbon scraper ring No actions required
Slight localized additive deposits at top edge
Localized smooth areas at lower edge
Carbon deposits on entire circumference between top piston ring and
lower edge of carbon scraper ring
First signs of marks left by top piston ring
Bright mark on entire circumference
Faultless, even honing pattern
First signs of marks left by lower cooling bores
Running pattern seems darker
Darker areas of even or varying color intensity Further endoscopic examination
Beginning and end of the discoloration are not sharply defined and do required as part of maintenance
not cover the entire stroke area work
Dark areas in the upper section of the cooling bore, remaining
circumference cannot be faulted
Piston rings cannot be faulted
On the entire circumference not only bright discoloration (not critical for Cylinder liner must be replaced;
operation) clearly visible darker stripes that begin at the top piston ring Service must be contacted
Heat discoloration in the direction of stroke and honing pattern damage
Heat discoloration of piston rings
1. Compile endoscopy report using the table.
2. Use technical terms for description of the liner surface ( Page 97).
3. Depending on findings:
Do not take any action or
carry out further endoscopic examination as part of maintenance work or
contact Service: cylinder liner must be replaced.
Final steps
1. Install injector ( Page 107).
2. Install cylinder-head cover ( Page 105).
M015715/00E 06-08 © MTU
Task Description 97
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 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 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-oclock and 12-oclock 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 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 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.
Seizures, Seizure marks 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.
M015715/00E 06-08 © MTU
98 Task Description
Evaluation of findings and further measures
The findings in the start phase of oxidation discoloration and heat discoloration are similar. Thorough investigation
and compliance with the above evaluation criteria allows a definite evaluation. To avoid unnecessary disassembly
work, it is recommended that another inspection be carried out after further operation of the engine.
M015715/00E 06-08 © MTU
