LO 8-6 Identify and outline the machining process to prepare the finish of a cylinder wall

LO 8-06: Identify and outline the machining process to prepare the finish of a cylinder wall.

 

Cylinder Wall Finish

Crosshatching is a special machined finish for cylinder walls used to provide a surface to retain oil and break in piston rings Figure 51. Because a cylinder is not perfectly symmetrical, the crosshatch will initially wear into the rings (and vice versa) to better conform to each other and produce a tighter seal between the two sliding parts.

Highly polished cylinder walls, with no crosshatch, will not allow residual oil to cling to the cylinder walls. Without the oil film on the cylinder walls, a gas-tight piston ring seal cannot be achieved. Consequently, poor sealing between the piston ring and the cylinder wall causes piston and ring scuffing as well as power loss due to blowby. Poor ring sealing also leads to high oil consumption.

FIGURE 08-51: Cylinder walls have a special machined finish called crosshatching . The crosshatch provides a surface for piston rings to wear into during the break-in period and retains oil for lubrication of the piston-to-cylinder wall.

FIGURE 08-52: Comparing crosshatch with plateau honing (left) and without plateau honing (right).

 

Cylinder crosshatch is produced when an engine is manufactured and through proper cylinder reconditioning processes during engine rebuild. Honing stones are used to produce the crosshatch finish of the cylinder walls.

To reduce the time and distance required for engine break-in, manufacturers use a process called plateau honing . This involves a final step of honing with a very fine abrasive stone or specialized nylon brush to remove the peaks of the cylinder crosshatch. Plateau honing also has the advantage of reducing engine oil consumption during break-in Figure 52.

	Technicians Tip
	Excessive idling of a diesel engine, sometimes just for a few minutes, will cause the crosshatch to fill with carbonized slobber. When the piston rings smooth out the slobber in a running engine, the crosshatch cannot retain oil and low compression results. This condition, when the cylinder wall crosshatch disappears, is called cylinder glazing . A glazed engine is accompanied by a low-power condition until it is operated under load for a few minutes to break up and burn out the glazed material from the crosshatch.

 

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