General information on inspecting cylinder walls - AH01.00-P-0300-01MM
ENGINE 278
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).
A magnet can be used to quickly check which type of cylinder barrel is involved, because cast iron cylinder barrels are magnetic and Silitec cylinder barrels are not.
Engine with Silitec cylinder barrel
Ideal condition
Matt gray surface, no honing pattern, dry cylinder barrel, no glossy sections or reflecting smooth spots.
It is also possible that irregularities can occur which should be individually assessed.
Individual score marks up fields of score marks
Caused by residual waste or soiling during company, e.g. through back pulsation of particle from the catalytic converter or the exhaust system.
Reuse crankcase.
Ring shaped imprints
Visible in the upper and lower piston ring reversal area are not a cause for concern.
Reuse crankcase.
Brown coloring of cylinder upper surface
Brown coloration (oil varnish) over large areas of the cylinder barrel indicates that the engine has been driven at a high temperature level.
This is normal and not a cause for complaint.
Reuse crankcase.
Glazing, smooth spots
Individual blank points, e.g. in middle of cylinder or in area of cylinder head bolts. Full circle impression at the upper and lower piston ring reversing points.
Reuse crankcase.
Optical steaks, friction marks
Starting from the first, second or third piston ring, run out after approx. 30 mm. Dry friction marks, imperceptible to the touch, caused by soot particles and oil film being washed off by fuel, e.g. during frequent cold starts associated with short-distance driving. These traces of friction marks which occur principally in area of cylinder head bolts and on pressure side are not a problem provided they are smoothed.
Reuse crankcase.
Impression on valve cooling bore for an 8 and 12 cylinder engine
The cooling bore in the crankcase shows a different coloration to the cylinder barrel.
Reuse crankcase.
Corrugated wear of the cylinder barrel
A washboard type surface structure of the cylinder barrel, partially or full perimeter.
Do not reuse the crankcase.
Rough streaks, friction scoring
Starting from first, second or third piston ring, tapering off only in bottom part of cylinder. Friction marks as described under "Optical streaks, friction marks" which have advanced to friction scoring.
If friction scoring is perceptible to the touch, the cylinder barrel is unusable.
Do not reuse the crankcase.
Piston scoring, ring scoring
Most of cylinder wall perceptibly roughened over the entire length.
Material deposits and perceptible scoring marks on cylinder wall and at piston skirt.
Cylinder barrel unusable.
Do not reuse the crankcase.
Engine with cast iron cylinder barrel
Glazing, smooth spots
Individual blank points, e.g. in the middle of the cylinder barrel or around the cylinder head bolts.
Reuse crankcase.
Visible stripes, friction marks
Starting from reverse area of the upper piston ring tapering downwards.
Traces of dry friction marks which cannot be felt, caused by oil film being washed off by fuel, for example from many cold starts when driving short distances.
Friction marks occurring mainly around the cylinder head bolts and on the pressure side are not a problem provided that they are smoothed out.
The piston rings are not damaged.
Reuse crankcase.
Ring shaped imprints
Visible imprints on cylinder barrel in the upper and lower reverse area of piston rings are not a cause for complaint.
Reuse crankcase.
Rotary bright, reflective, polished upper surfaces of cylinder
Starting from the reverse area of the upper piston ring with measurable, partial cylinder wear.
The cylinder barrel is unusable.
Do not reuse the crankcase.
Rough streaks, friction scoring
Starting from first and second piston ring, tapering to an end only in bottom part of cylinder. Progressive signs of friction lead to friction score marks.
Where these signs of friction are perceptible, the cylinder barrel is unusable.
The piston rings may be damaged.
Do not reuse the crankcase.
Continuous individual traces of scratch
Caused by soiling, for example, by the back-pulsation of soot particles from the catalytic converter or exhaust.
Reuse crankcase.
Piston seizure
Most of cylinder wall perceptibly roughened over the entire length.
Material deposits and perceptible scoring marks on cylinder wall and at piston skirt.
The cylinder barrel is unusable.
Do not reuse the crankcase.
Brown coloring of cylinder upper surface
A brown coloration over large areas of the cylinder barrel is oil varnish and indicates that the engine has been driven at a high temperature level.
Oil varnish above piston ring zone is normal and is not a reason for complaint.
Reuse crankcase provided no impermissible cylinder distortion is present.