Honing is an abrasive process which leaves small scratches on the surface of the cylinder bore. The depth of the scratches is determined by the grit size of the abrasive method being used. Oil is trapped in the scratches and provides lubrication during running-in and normal engine operation.
The cylinders of aluminium cylinder blocks can be restored by honing but, for some engines, the manufacturers do not recommend re-boring.
There are two types of cylinder hones. One has rigid stones and the other has a large number of small beads of abrasive arranged in the form of a brush. Hone stones are made of aluminium oxide or silicon carbide, both are very hard abrasives.
Before using a hone, all exposed parts, such as the crankshaft, should be covered with oil-soaked rags that will hold dust and particles of abrasive. The cylinders should he cleaned carefully after honing, as any abrasive material left behind will damage the engine.
Hones are driven by a portable electric drill. This rotates the hone while the operator moves it up and down in the cylinder bore to produce a cross-hatch pattern on the cylinder wall (Figure 5.7).
2. Shake the hone to make sure that all the stones contact the cylinder wall.
3. If the hone shakes, remove it and pack behind the low stones to get rid of the shake.
4. Operate the hone for about two strokes, and again try the hone for shake. Check it in another bore and. if satisfactory, proceed to hone. Lubricate the stones during use.
5. Use a slow drill speed and adjust the up-and-down movement so that the desired cross-hatch pattern is obtained. If the vertical movement is too slow or too short, the angle of the pattern will be too flat.
This type of hone consists of a central shaft with a cylindrical brush head. Small abrasive beads are attached to the ends of nylon filaments to form the head of the brush (Figure 5.9). The hones are made in a number of sizes with different abrasives. Each hone size is suitable for a range of cylinder sizes.
The hone is driven by an electric drill and operated up and down the cylinder to produce the desired crosshatch pattern.
|Fig 5.10 (a & b)|
A recommended cleaning method is:
I. Clean the bores with detergent and water and a stiff brush.
2. Rinse with clean water and dry with a clean cloth.
3. Wipe the bores with a clean cloth that has been dipped in engine oil.