Engine - Cylinder Wall Inspection
Date: May 19, 2009
Order No.: S-B-01.00/27
Group: 01
SUBJECT:
MY-All, Models with Engines 112, 113, 137, 272, 273, 275
Cylinder Barrel Inspection
Cylinder Wall Inspection
If engine complaints regarding noises, overheating, or oil consumption arise, visually inspect the mounted cylinder head with a light probe and
endoscope (bore scope). If visual inspection with an endoscope is not sufficient, consult the following documents in WIS: "Check compression
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 374
pressure" and "Check cylinder leakage" before removing the cylinder head (WIS documents AR01.00-P-1300, AR01.00-P-0200, AR01.00-P-1200,
AR01.40P9201AA, etc.).
When inspecting Silitec barrels with a light probe it is absolutely essential to observe all possible scenarios before removing an engine or replacing a
crankcase. Section A describes acceptable cylinder barrel wear and section B describes the cases where cylinder barrels are deemed unacceptable
and the crankcase should be replaced.
Ideal (Normal) Cylinder Wall Condition
The ideal is a matte gray surface, no honing pattern, and a dry cylinder barrel without polished sections or mirror polished flats. Individually assess
any irregularities (Figure 1).
Note:
Do not replace crank case based on suspicions only. Perform checks and / or repairs according to published WIS, DTBs, and other official
documents. If other than crankcase components are determined to be a cause of complaint, replace only affected components.
Note:
Use only approved methods to remove any carbon deposits when performing a repair. Do not use any sand paper, abrasive pads or disks or grinding
and sanding tools. Use only approved fuel additives. Dealers might be debited when performing unapproved or incorrect repairs as well as when
unnecessarily replacing parts.
Deviations
DEVIATIONS
A. Cylinder Wall Deviations from Normal Wear Where Crankcase Can Continue to be Used For any deviations from normal wear and tolerance
values, document the direction of the leakage while checking the leak tightness of the cylinder (in the direction valve or in the direction of the
crankcase). In the case of deviating compression pressure values, in particular when not achieving the installation tolerance/new values (measured
with a compression recorder), one should check for indications of a fluid lock (e.g. wet piston crown, wet air filter, water-oil-glycol residues).
In the following cases of deviation, continue to use the crankcase.
1. Individual or Fields of Score Marks
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 375
In cases where individual or fields of score marks (Figure 2), (usually caused by residual waste or soiling through back pulsation of particle from the
catalytic converter or the exhaust system), continue to use the crankcase.
2. Ring Shaped Imprints
In cases where upper and lower reversal range of piston rings (Figure 3), continue to use the crankcase.
3. Brown Coloration at Upper Cylinder
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 376
In cases where brown coloration (Figure 4) (oil varnish) over large areas of the cylinder barrel, (which indicates that the engine has been driven at a
high temperature level); continue to use the crankcase.
4. Pressure Gloss Marks and Smooth Spots
In cases where individual blank points (Figure 5), as on the middle of the cylinder or around the cylinder head bolts or an all-round impression at the
piston ring reversing point above and below; continue to use the crankcase.
5. Optical Stripes, Friction Marks
In cases where dry friction marks (Figure 6), which cannot be felt, which start from the first, second or third piston ring and run out after approx. 30
mm; continue to use the crankcase.
NOTE:
These traces of friction marks which occur principally around the cylinder head bolts and on pressure side are not a problem provided they are
smoothed. They are caused by soot particles and oil film being washed off by fuel as a result of frequent cold starts associated with short-distance
driving.
6. Imprint on Valve Cooling Bore for an 8- and 12- Cylinder Engine
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 377
In cases where the cooling bore in the crankcase shows a different coloration (Figure 7) than the cylinder barrel; continue to use the crankcase.
B. Deviations Necessitating Replacing the Crankcase
1. Corrugated Wear of the Cylinder Barrel In cases where the cylinder barrel surface has a washboard appearance (Figure 8), partially or all around;
do not use the crankcase anymore.
2. Roughened Mottling, Friction Scoring
2000 Mercedes Benz CLK 320 (208.365) V6-3.2L (112.940) Page 378
If friction eroded marks or streaks (Figure 9) are observed starting from the first, second or third piston ring and taper down to the cylinder bottom,
the cylinder barrel is unusable and the crankcase should no longer be used.
3. Piston seizure, eroded areas on the ring
Most of cylinder wall perceptibly roughened over the entire length (Figure 10). Material deposits and perceptible scoring marks on cylinder wall and
at piston skirt. The cylinder barrel is unusable and the crankcase should no longer be used.
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