After extended use, cylinder liners of both 4-stroke, and 2-stroke engines will show signs of wear and tear. This wear is not evenly distributed. Most of the wear occurs between the reversal points of the upper and lower piston rings. Often we find scuffing marks where the upper piston ring changes direction. Also most cylinder liners, especially those of 4-stroke engines, will become slightly oval over time.
Another effect of this wear is increased lubricating oil consumption. When a cylinder liner comes out of the factory, it will have a slight cross-hatch pattern honed into it’s surface. This increased roughness helps the liner surface to retain the lubricating oil needed to provide an evenly distributed oil film between the piston ring reversal points. If the surface becomes too smooth due to wear and/or glazing of the surface, the piston rings will easier break the oil film, causing even more wear. Also any excess oil will no longer be retained by the liner surface, and burn off in stead, causing increased lubricating oil consumption.
If the total amount of wear is still within the rejection criteria as given by the manufacturer, the liners can be reconditioned. When we get them in our workshop, we will first clean and measure them. All measurements go into special protocol sheets. The next step is using a honing machine to make the cylinder bore round again, with a slightly bigger diameter, and restore the surface roughness needed to retain sufficient lube oil. Our honing machine can handle cylinder liners up to a diameter of 1 meter. The machine is made by the Swedish company Chris Marine. Here is a brief description of one of their typical honing machines: honing-machine.pdf
The pictures show a liner of a MAN B&W K80MC (this is a marine 2-stroke engine with a cylinder bore of 800mm). The first as we receive it in our workshop, the second with the liner in the honing pit with the honing machine inserted.
Finally the cylinder liner is measured again. Sometimes the landing surfaces between liner and cylinder cover, or liner and engine frame need to be skimmed on the lathe, to ensure the correct flatness of the sealing surfaces. Diameters, surface roughness, and other critical dimensions are recorded, and if everything is within the right tolerances, the liner is packed and shipped back on board again.
If necessary we can also transport our honing machine on board, and perform the honing in-situ, while the liner is still in the engine.