AH01.40-B-0001-03A | Notes for evaluation of a cylinder barrel | Engine 457.9, 460.9, 904.9, 924.9, 906.9, 926.9 | |
The following indications help on the evaluation of the cylinder wall to make a technical decision, on the condition and possible reutilization of the engine block or engine cylinder liner.
In a new engine, the wall is cylindrical, with the operation time a natural wear occurs.
The cylinder wall does not wear uniformly, it becomes conical with normal wear.
The honed cylinder wall can also be identified for wear or damage.
The images represented next are only to illustrate the possible types of cylinder wall damages. In the evaluation of the types of damage, for a diagnosis, the surface condition of the piston and of the rings is always to be considered.
Wear or damages on the cylinder wall are frequently caused by:
Leakage in the intake air ducts after the air cleaner;
failures in the fuel injection system;
too small or too large clearance between the piston skirt and the cylinder wall during operation;
poor engine oil quality (oil viscosity) or engine oil dilution by fuel;
damaged or dirty engine oil filter;
fault in the engine oil circuit, too low engine oil pressure, for instance; and
deformed or damaged oil injection nozzles for piston cooling.
After a repair, before starting the engine, fill the oil circuit, by auxiliary means, with approved oil. Next, crank the engine several times through the starter, without permitting engine firing, actuating simultaneously the keys ("START" and "STOP"), until engine oil pressure is obtained.
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Normal state
Opaque gray surface, honed area visible, dry cylinder wall, without oil residue, without polished or mirrored regions. The cylinders or cylinder liner walls must not present traces of burns. Light scores are not critical.
The honed surface is more or less visible in the entire extension of the cylinder. At the reversion point of the first piston ring, the honed area may be partially worn.
The engine cylinder or cylinder liner nay be re-utilized.
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Only for the engines 904.9, 906.9, 924.9, 926.9
The striae in the top area (arrows) of the cylinder wall, formed by induction hardening in the manufacture of the block, is to be considered normal.
The greater the engine operating time, smaller is the visualization of the striae (arrows).
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Carbon deposit on the cylinder wall
Check the fire area on the cylinder wall or cylinder liner wall of the engine for the existence of carbon (arrow).
In the presence of carbon (arrow) in the fire area:
- Clean the fire area and re-utilize the cylinder liner or cylinder of the engine block.
- additionally remove the piston and assess the piston rings.
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Continuous and isolated marks of scratches or scores
Check the running surface of the cylinder liner or of the engine cylinder for marks of scratches or scores (arrows).
In the case of light marks (arrows), the cylinder liner or the engine cylinder may be re-utilized.
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Marks in the shape of rings
At the top and bottom piston ring reversion point color tones are visible (arrow), the honing image can still be observed.
The engine cylinder or cylinder liner may be re-utilized.
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Areas with mirrored or polished marks
Isolated polished marks, for example, in the center of the cylinder wall (arrow) or a mark around the top and bottom reversion point of the piston ring.
The cause may be poor engine oil quality.
Engine 457.9, 460.9:
The engine cylinder liner is destroyed and has to be replaced.
Engines 904.9, 906.9, 924.9, 926.9:
Replace or machine the engine block, additionally remove the piston and assess the piston tings.
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Visible scores, traces of friction
Traces of dry friction or formation of bands (arrow) on the cylinder wall as from the second or third piston ring, in the entire extension ending at the bottom.
Caused by soot particles and washing of the oil film by fuel.
Damaged piston rings may also be the cause.
Engine 457.9, 460.9:
The cylinder liner and the piston are destroyed and have to be replaced.
Engine 924.9, 926.9:
Replace or machine the engine block.
Pistons and rings are to be replaced.
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Damages by dust
The honing marks are no longer visible or are nearly erased by the polishing. At advanced wear a step is noticed at the top reversion point of the first piston ring (arrow).
Engine 457.9, 460.9:
The engine cylinder liner is destroyed and has to be replaced.
Engines 904.9, 906.9, 924.9, 926.9:
Replace or machine the engine block.
Pistons and rings are to be replaced.
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Piston seizing or rough scores, seizing by friction
Normally a roughness is noticed on the entire extension of the cylinder wall. Stock sediment and perceptible marks of seizing on the cylinder wall and also on the piston skirt.
Engine 457.9, 460.9:
The engine cylinder liner and the piston are destroyed and have to be replaced.
Engines 904.9, 906.9, 924.9, 926.9:
Replace or machine the engine block.
Pistons and rings are to be replaced.