Popular Hot Rodding - Boring the Mystery out of Machining

Once considered exotic, but now thought of as common practice, is bolting a torque plate to the deck surface while honing. The process simulates the distortion a block experiences when a cylinder head is bolted into place, and is just another measure used to make sure the bores are as round as possible. Likewise, another procedure becoming more common and accepted for street motors is plateau honing, or honing in multiple stages. As the name suggests, an initial coarse honing stone is followed up by several finer grit stones in different stages to flatten the peaks in the finish. The result is deeper valleys that improve oil retention and lubrication for the pistons and rings, in addition to providing a smooth surface. "Almost all performance engines these days are plateau–honed," says Pat. "As far as the grit of the stones they’re using, everyone has their own method, so it’s somewhat secretive."

Based on bore size and cylinder length, the machinists can set the rotational rate and dwell rate of the shaft

Based on bore size and cylinder length, the machinists can set the rotational rate and the dwell rate of the shaft. It’s hinged on a series of universal joints to position it straight within the bore. Allowing the block to cool every 10 to 15 minutes prevents the block from distorting.


A knob at the top of the honing machine controls the amount of tension the stones exert on the cylinder walls.

A knob at the top of the honing machine controls the amount of tension the stones exert on the cylinder walls. A meter that measures the load on the motor in amps (or percent) helps the machinist to estimate, by seeing, in addition to feeling, how much progress is being made. Between rounds of honing, a dial–bore indicator is used for a definitive answer. This proves is repeated several times with different stones until the final finish and bore size is reached, and total honing time ranges from one to one–and–a–half hours.

There is still some debate, however, regarding hot honing. It involves heating up the honing oil to roughly 200 degrees to simulate the expansion a block experiences at operating temperature. As with the use of torque plates, the idea is to get the bores as round as possible, but not everyone’s convinced. "Some guys swear by it, but other guys try it once and never do it again."

Decking

To promote proper cylinder–head sealing, the deck of the block is often surfaced, or decked, to provide a smooth, even surface for the gaskets and heads. As with boring, it is critical that the deck is machined perpendicularly to the crankshaft centerline. Since the pistons sit below the deck at top dead–center in most production blocks, the deck height is often reduced to improve quench and raise the static compression ratio.

Before decking begins, a dial gauge is run across the surface in numberous spots to make sure it's completely flat.

It may look like a plain piece of square tubing, but the bar the mains locate off of on a Sunnen HBS–2100 is a highly precise piece that costs about $400 to replace. Before decking begins, a dial gauge is run across the surface in numerous spots to make sure it’s completely flat. The gold clamps on each side can adjust the angle the bar sits at if necessary.


The speed the cutter rotates at and the rate at which it moves across the deck from front to back are manually adjustable.

Actually positioning the cutting head into place requires a delicate touch and lots of experience. It is lowered until it just barely touches the deck surface, then the machine goes to work. The speed the cutter rotates at and the rate at which it moves across the deck from front to back are manually adjustable. After each swipe, a dial gauge is used to track progress, and entire process takes about an hour.