For example: the Ford 302 came with either a 28oz or 50oz imbalance from the factory depending on the year. This means that the balancer and the flywheel are off balance by that amount due to added counterweighting. The crank is also off by this same amount due to lack of counterweighting. Put them together and you have a balanced assembly.
The crank couterweights are are trimmed to offset the weight of the piston and rod assembly. The imbalanced cranks are due to factors such as size and/or manufacturing cost. There is not enough material to balance the piston and rod assembly so they add extra counterweight instead to the outside of the engine, the balancer and the flywheel.
I believe the F20C is neutral balanced meaning that the balancer anf flywheel do not help to balance the engine. In this case, the harmonic balancer doesn't balance the engine, it only absorbs harmonic frequencies.

 

Yeah, I forgot to mention when I had the pulley balanced I had the entire assemble balanced (i.e crank, pistons, rods, flywheel, pulley)

it cost about 250 to have it all done, and was well worth the investment!

 

I also had one of their hydro pulleys fail... same situation as the post above... I would never buy anything from them again.... especially not a crank pulley... too much at risk... Luckily I had kept the stock pulley in my car under the passanger seat, and I carry a socket set in the car just in case... build quality sucks, and no, I didn't over torque the bolts...

 

The term Harmonic balancer is a misnomer.

the device is a harmonic dampner.

Regardless of how well you balance your rotating assembly there will still be rpm's at which your crank will have a natural frequency of vibration. Think of a tuning fork, it has a natural frequency...or tone that it vibrates at. the crank is the same way. although it is very strong forged steel it still has a natural frequency. the goal of the factory front pulley is to "dampen" out the natural frequencies of the crank. Not to "balance" the crank.