General information on inspecting cylinder walls - AH01.00-P-0300-01AMG

ENGINE 133, 156, 177, 178, 276.8 

General information 

If a complaint is made about an engine, for example because of noises, overheating, oil consumption etc., perform a visual inspection of the mounted cylinder head by lighting it with an endoscope. The following notes should be helpful in assessing the cylinder barrels to allow a professional decision to be made about the condition and further use of the crankcase. If this can cannot be assessed with sufficient certainty through inspection using an endoscope, then the "Check compression pressure" and "Check cylinder leakage" operations must be performed before removal of the cylinder head.

The results of the check must be documented on a repair order. In case of deviations from the prescribed wear and tolerance values, the cylinder leakage check must focus on determining the direction of leakage (towards valve or towards crankcase).

In case of deviating compression pressure values, in particular if the measurements taken with a compression recorder are below the installation tolerance and/or new values, a check must be made for signs of a fluid lock (e.g. wet piston crown, wet air filter, water-oil-glycol residues).

Crankcase with LDS coating (LDS = twin-wire arc-sprayed coating) 

In cylinder crankcases with LDS coating, an electric arc is used to seal off iron-carbon wires, to then spray them through an inert gas stream onto the inside of the cylinder. The resulting characteristic pores generate a retained oil volume in the surface, which in turn enables the reliable use of an extremely smooth, reflective honing structure.

Comparison between cylinder barrel with LDS coating, cylinder liners with Silitec cylinder barrel and cast iron cylinder barrels 

Cylinder barrel with LDS coating (LDS = twin-wire arc-sprayed coating) 

Cylinder barrels with LDS coating can be recognized by their reflective surface with pores (see white dots in the illustration) and the honing pattern.

The piston can be reflected in the barrel surface.

Fig 1: Identifying Cylinder Barrels With LDS Coating

Courtesy of MERCEDES-BENZ USA

Example of cylinder liners with Silitec cylinder barrel 

Fig 2: Identifying Cylinder Liners With Silitec Cylinder Barrel

Courtesy of MERCEDES-BENZ USA

The cylinder barrel has a dull, gray high-gloss surface and the honing pattern is hardly perceptible.

Example of cast iron cylinder barrel 

The cast iron cylinder barrel has a metallic, high-gloss surface and a clearly-shaped honing pattern.

Fig 3: Identifying Cast Iron Cylinder Barrel

Courtesy of MERCEDES-BENZ USA

There now follows some notes on checking cylinder barrels with LDS coating (twin-wire arc-sprayed coating) 

Visible pores (white dots) 

White dots or pores distributed over the entire cylinder barrel are typical for cylinder barrels with LDS coating.

Cylinder crankcase can be used again.

Fig 4: Identifying Visible Pores On Cast Iron Cylinder Barrel

Courtesy of MERCEDES-BENZ USA

Large-area rust or corrosion spots 

Rust symptoms in center of cylinder barrel

Cylinder crankcase can be used again.

Fig 5: Identifying Large-Area Rust/Corrosion Spots

Courtesy of MERCEDES-BENZ USA

Individual corrosion spots 

Individually-occurring corrosion spots over entire cylinder barrel, can also occur as cavities.

Cylinder crankcase can be used again.

Fig 6: Identifying Cylinder Barrel Individual Corrosion Spots

Courtesy of MERCEDES-BENZ USA

Optical strips and easily recognizable honing pattern 

Visible rust strips in upper piston ring reversal area of cylinder barrel and clearly recognizable honing pattern.

Cylinder crankcase can be used again.

Fig 7: Identifying Cylinder Barrel Optical Strips And Honing Pattern

Courtesy of MERCEDES-BENZ USA

Ring shaped corrosion on cylinder barrel 

Ring shaped corrosion in area o flower piston ring reversal area on cylinder barrel.

Cylinder crankcase can be used again.

Fig 8: Identifying Cylinder Barrel Ring Shaped Corrosion

Courtesy of MERCEDES-BENZ USA

Partial corrosion on cylinder barrel 

Partial corrosion in cylinder barrel.

Cylinder crankcase can be used again.

Fig 9: Identifying Partial Corrosion On Cylinder Barrel

Courtesy of MERCEDES-BENZ USA

Honing marks in cylinder barrel 

Honing marks, recess developed in cylinder barrel in honing angle, through machining without any bulging.

Cylinder crankcase can be used again.

Fig 10: Identifying Cylinder Barrel Honing Marks

Courtesy of MERCEDES-BENZ USA

Illustration of valve cooling bore in cylinder barrel 

Shading in cylinder barrel in cylinder wall area in development direction of valve cooling bore after run time (score marks and honing pattern recognizable).

Cylinder crankcase can be used again.

Fig 11: Identifying Valve Cooling Bore Area In Cylinder Barrel

Courtesy of MERCEDES-BENZ USA

Crack in cylinder barrel 

Crack in cylinder barrel running in longitudinal direction with coolant leakage after detaching coolant chamber on the cylinder crankcase.

Cylinder crankcase may not be used again.

Fig 12: Identifying Cylinder Barrel Crack

Courtesy of MERCEDES-BENZ USA

Local layer separation on cylinder barrel 

Planar limited separation of layer on cylinder barrel because of insufficient layer bonding.

Cylinder crankcase may not be used again.

Fig 13: Identifying Local Layer Separation On Cylinder Barrel

Courtesy of MERCEDES-BENZ USA