Hone cylinders

Part 1. Preparation and safety

Objective

• Hone the cylinders to operational condition.

Personal safety

Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:

• Work clothing - such as coveralls and steel-capped footwear
• Eye protection - such as safety glasses and face masks
• Ear protection - such as earmuffs and earplugs
• Hand protection - such as rubber gloves and barrier cream
• Respiratory equipment - such as face masks and valved respirators

If you are not certain what is appropriate or required, ask your supervisor.

Safety check

• Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.

Points to note

• Ensure that the bore is left totally clean, any foreign particles can cause damage to the assembled engine.

Part 2: Step-by-step instruction

1. Measure pistons
   Just before they are reconnected to their rods, the pistons are measured so that the final bore size can be determined for the honing process.
   On pistons with uncoated skirts, the diameter is measured on the skirt with a micrometer. When the exact size of the piston is known, the machinist will then know the finished size to hone the cylinder walls.
2. Coarse grit hone
   The honing process does two things: First, it enlarges the cylinder bore to the exact size that is needed to give the specified amount of clearance between the piston and the cylinder wall. Second, it leaves a fine crosshatch pattern of light scratches on the walls of the cylinder that are necessary to retain microscopic beads of oil. This film of oil seals the piston rings to the cylinder walls and keep the compression inside the combustion chambers.
   As the stones go up and down in the cylinders, the machine flashes a light when the stones are at the bottom of the bore and a meter tells the machinist how heavy the load on the stones is. It is the balance between the speed of the stroke and the load on the meter that returns the cylinder to a perfectly straight and round bore.
   A dial bore gauge is used frequently during the honing process.
3. Fine grit hone
   There are three grades of stone used during the honing, and when the size of the bore reaches specific points, the machinist changes to a finer grit stone to slow down the metal removal and provide a smoother surface.
   When one side is complete, the block is flipped over and all three grades of stone are used on the other four bores.
4. Brush clean
   When all the cylinders are within tolerance, the stones are changed for some brushes that will be run with the honing oil to clean as much of the grit out of the crosshatches as possible before the final wash.