Part 1. Preparation and safety
Objective
- Machine the cylinder block 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
- The machining process removes material and this causes heat to build up in the component. Always allow breaks in the machining process so that components can cool.
Part 2: Step-by-step instruction
- Hone the main bearing saddle
The main caps need to be removed first so that a small amount can be ground off the bottoms of the seats of the caps. Then the caps are put back on the block and tightened and torqued to spec. Now the opening is no longer circular, it's a slight oval.
The size is checked with a dial bore gauge and the honing stones are inserted and expanded until the proper drag is felt. The honing drill is lined up with the stones and once the oil starts to flow through the tube above the block, the stones are passed in and out while the drill is running so that metal is removed and the oval shape begins to return to a perfect circle.
As the stones take off metal, the block and caps begin to heat up and the machinist checks the size with a gauge and takes a break to let the block sit and cool so the metal will return to its true size.
After a few minutes of cooling, the stones are run again and progress is checked with a gauge. Then the block is lifted and turned around so that the hone can be finalized to the perfect size from the other side.
This is the first process for the block because the next two machining procedures depend on a perfectly straight line through the main bearing bore for proper mounting to the machine.
- Level the block decks
Next, the alignment dowels for the heads are removed and the block deck is leveled. When the deck is perfectly level the cutting machine is started and it runs by itself at a set pace, shaving the surface to make the deck perfectly flat so that the new head gaskets will have no problem sealing out water, air or oil leaks.
When one deck is done, the block is rotated and the machine is setup again. Both decks must be cut the same amount or there will be a difference in the compression ration from one side of the motor to the other and the intake manifold won't fit properly. The amount removed in this case was so tiny that the factory number stamping of the block ID was even still visible.
- Bore the cylinders
Using the same mounting point through the main bearing bore, the block deck is now leveled in the boring machine. The machine needs to be set in the approximate centerline of the first cylinder bore. Then the machinist tells the machine what type of engine this is and presses go. The machine takes care of the rest for the first half of the block. This particular machine centers itself in the bore and the cutting tool for the proper overbore size which was already set up in the spindle goes to work once it starts to spin.
The boring machine knows how far to go down in the bore for each engine type that is programmed in and when one bore is done it retracts the spindle and automatically moves to the next bore and centers itself once again. It goes through and cuts all four of the bores to size for this side of the block.
The block is then lifted out and flipped to the other side to get finished. A piston bore that is still the original diameter as when it left the factory is said to be standard size.
Pistons are manufactured for oversized bores in increments of ten, twenty, thirty, forty and sixty thousands of an inch, or in increments of point two five or a quarter of a millimeter, up to one and a half millimeters.
The boring machine will cut the cylinder wall to fractionally less than whatever bore you will need and the honing machine will later expand it to the exact specification.
