Polishing the crank journals is done to reduce friction and make the journal perfectly smooth to the Nth Degree...A loose bearing clearance, within spec of course, is ideal for a motor...This will allow for proper lubrication and minimum friction...The Crank rotates on a Simple Bearing similar to a tire hydroplaning on a wet puddle...If the puddle isn't deep enough, the tire will not hydroplane and if the puddle is too deep, the tire will be out of control...

You want the puddle to be the most perfect depth and with enough speed, you can travel over it without touching the bottom and without throwing the car out of its line...

The polishing of the crank allows for it to glide right over the oil flow as it is pushed thru the oil holes of the bearing or rod journal and reaches the rotating crank journal...

When that spinning crank hits the bearing, you will a severly damaging event...The bearing is pushed into the block or rod as the crank jounal is pushed into the bearing...This is why we say it has a "spun" journal or "spun" bearing...

This causes material to pack up and block the oil holes and you will lose oil pressure...This also forces fragments of the metal from the crank journal and the bearing throughout the engine...It usually will collect in the oil filter and the oil pickup...

This is not the end of the crankshaft though...A machinist is able to weld material onto the crankshaft's journal and then grind and polish it down to a smooth and perfect surface as if it were new...Then he will "Line Bore" the mains and/or rods to allow for a perfect fit onto the crank's journals...Then he will get the proper sized bearings to meet the assembly spec given by the manufacturer...

Now, this repair procedure is what is practiced in the majority of the Internal Combustion Engine World, but, Honda Crankshafts tend to let go the welded-on material and the crankshaft is officially scrapped...

Most Forged Crankshafts are not repairable or at least the machinist will not warrannty the work if the journals must be welded...

You can also stroke/destroke motors cranks by using this method as well...

Balancing of the crankshaft is done on a rotating fixture that simulates the engine's rotation...The machinist will remove material from the CrankShaft to achieve the minimum Harmonic to, again, reduce friction...

The proper way to balance the bottom end is to properly match the pistons' and the rods' weights', respectively...Then assemble them onto the crankshaft and then balance the crank with the entire rotating assembly, all as one unit...

Zee