Diesel engine 12V 4000 G73, 16V 4000 G73. Manual - part 17
Findings
Measure
Burn mark
This is caused by a malfunction 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 2 onwards and less pro‐
nounced from TDC-ring 1. The honing pattern is usually no longer visible and
displays a clearly defined (straight) edge to the undisturbed surface. The dam‐
aged surface is usually discolored. The circumferential length varies.
Liners with burn marks, or heat discoloration, starting in TDC ring 1 have to be
replaced.
Seizure marks, scuff‐
ing
Irregular circumference lengths and depths. Can be caused either by the pis‐
ton skirt or the piston crown. Material deposits on the liner (smear), heavy dis‐
coloration. Severe, visible scoring.
Replace liner.
Evaluation of findings and further measures
The findings in the start phase of oxidation discoloration and heat discoloration are similar. A thorough
investigation and compliance with the above evaluation criteria allow an unambiguous evaluation. To
avoid unnecessary disassembly work, it is recommended that another inspection be carried out after fur‐
ther operation of the engine.