Diesel engine 12V 4000 G73, 16V 4000 G73. Manual - part 16

7.1.3 Engine – Test run

DANGER

Unguarded rotating and moving engine components.

Risk of serious injury – danger to life!

• Before barring or starting the engine, make sure that nobody is in the danger zone.

WARNING

Engine noise above 85 dB (A).

Risk of damage to hearing!

• Wear ear protectors.

Engine – Test run

1.

Start engine (→ Page 32).

2.

Perform test run not below 1/3 load and at least until steady-state temperature is reached.

3.

Carry out operational checks (→ Page 34).

4.

Stop engine (→ Page 35).

7.2 Cylinder Liner

7.2.1 Cylinder liner – Endoscopic examination

Preconditions

☑ Engine is stopped and starting disabled.

Special tools, Material, Spare parts

Designation / Use

Part No.

Qty.

Rigid endoscope

Y20097353

1

Preparatory steps

1.

Remove cylinder head cover (→ Page 76).

2.

Remove injector (→ Page 79).

Positioning crankshaft at BDC

1.

Using barring device, turn crankshaft until crankshaft journal of the cylinder to be inspected has reached

BDC.

2.

Insert endoscope into cylinder liner through injector seat.

Endoscopic examination of cylinder liner

Findings

Action

• Thin carbon coating on circumference of carbon scraper ring

• Slight localized additive deposits at top edge

• Localized smooth areas at bottom edge

• Carbon deposits on circumference in clearance between top piston

ring and bottom edge of carbon scraper ring

• First signs of marks left by top piston ring

• Bright mark on entire circumference

• Consistent honing pattern without objections

• First signs of marks left by lower cooling bores

• Running pattern seems darker

No action required

• Dark areas with even or varying degrees of discoloration

• Beginning and end of the discoloration are not sharply defined and

do not cover the entire stroke area

• Dark areas in the upper section of the cooling bore, remaining cir‐

cumference without objections

• Piston rings without objections

Further endoscopic examina‐

tion required as part of main‐

tenance work

• On the entire circumference, apart from light areas of discoloration

(that do not impair operation) clearly darker stripes that start at the

top piston ring

• Heat discoloration in the direction of stroke and honing pattern dam‐

age

• Heat discoloration of piston rings

Cylinder liner must be re‐

placed; Service must be con‐

tacted

1.

Compile endoscopy report using the table.

2.

Use technical terms for description of the liner surface (→ Page 68).

3.

Depending on findings:

• Do not take any action or

• carry out a further endoscopic examination as part of maintenance work or

• contact Service; cylinder liner must be replaced.

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Final steps

1.

Install injector (→ Page 79).

2.

Install cylinder head cover (→ Page 76).

7.2.2 Cylinder liner - Instructions and comments on endoscopic and visual

examination

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

Measure

Minor dirt scores

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.

Single scores

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.

Scored area

These areas consist of scores of different length and depth next to one anoth‐

er. In most cases, they are found at the 6-o'clock and 12-o'clock positions (in‐

let/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.

Bright area

Bright 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 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 interrupt‐

ed.
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 is corrosion pitting.

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.
Cylinder liners with a large number of black lines around the running surface

have limited service life and should be replaced.

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