I have a 2003 Hyundai Tiburon 2.7L. Harmonic Balancer is loose. The car looses power. The serpentine belt comes off the pully. The vehicles starts but only the bottom pully turns I believe it is the crankshaft pully. Any suggestions or ideas of the cause or what to check?

A harmonic balancer (sometimes referred to as a "vibration damper") is a relatively simple component comprised of three pieces; inner hub, rubber isolator and outer inertia ring. Although the isolator separates the hub and inertia ring, the part looks and feels like one solid piece with no moving parts. While the engine is running however, combustion events in the cylinders cause the the crankshaft to twist back-and-forth which in turn oscillates the hub away from the inertia ring; the rubber isolator is then stretched and absorbs the harmful vibrations. As the harmonic balancer ages and wears from vibration, the isolator can begin to tear resulting in what appears to be a loose and wobbly pulley. To resolve, the serpentine belts must be removed, harmonic balancer unbolted and replaced with new part. You can read more here: https://www.yourmechanic.com/article/how-to-replace-a-harmonic-balancer-by-richard-zeppetini

There is one bolt in center of pulley/harmonic balancer. Sounds like the harmonic balancer has started going bad..if bolt in center of pulley is loose...which is fairly uncommon tighten which you just tighten Iike any other bolt. If it is tight then you will need the replacement. Replacement is a good bit more involved. Radiator has to be removed, special tool, harmonic balancer pulley remover is required..it will remove pulley. Then you line up pulley with keyway..tap on with rubber hammer until pulley is on far enough for bolt to be started..tighten the bolt and it pulls the pulley all the way into place.

More info please ! Steering wheel wont shake in park if vehicle not moving. But to hazard a guess without knowing make year are model would not be possible .

how this happen,get loose it self.

It sounds like the harmonic balancer came apart. This is a two part pulley seperated by a rubber gasket. The part itself is much less expensive at auto parts stores than the dealership but you may need to wait a few days for it to arrive as most stores won't have the part in stock. A picture of the harmonic balancer is below:

2004 SANTA FE HARMONIC BALANCER

You can go to autozone.com and register for free for free online repair manual for your vehicle. Also google images have pics. There are also more manuals here:
http://manualspace.com/manual/search/89-toyota-celica-gt-repair-manual-online-pdf.htm

03 should still be under warrenty, if not check belt and power steering pulley if loose or wobbling need repair

REMOVE OR DISCONNECT

1. Serpentine belt from the crankshaft pulley.
2. Raise the vehicle on a hoist.
3. Right front tire and wheel assembly.
4. Right inner fender access cover.
5. Using a 28 mm socket, remove the crankshaft harmonic balancer retaining bolt.
6. Crankshaft harmonic balancer using tool J 38192 or equivalent.
7. Sensor electrical connector.
8. Foreign object deflector.
9. Sensor and pedestal from block face.
10. Sensor from pedestal.

INSTALL OR CONNECT:

1. Loosely install the crankshaft sensor on the pedestal.
2. Position the sensor with pedestal attached on special Tool J 37089.
3. Position the special tool on the crankshaft.
4. Bolts to hold the pedestal to the block face, torque to 20-40 Nm (14-28 lb.ft).
5. Torque the pedestal pinch bolt to 3-4 Nm (38-40 lb.in).
6. Remove special tool J 37089.
7. Place the special tool 37089 on the harmonic balancer and turn. If any vane of the harmonic balancer touches the tool, replace the balancer assembly.
8. Balancer on the crankshaft.

• Apply thread sealer (GM 1052080) or equivalent to the threads of the balancer bolt.

1. Torque the crankshaft bolt to 140 Nm + 56°(104 lb.ft + 56°).
2. Foreign object deflector.
3. Electrical connector.
4. Inner fender shield.
5. Tire and wheel assembly, torque to 140 Nm (104 lb.ft).
6. Lower the vehicle.
7. Serpentine belt.

You have to replace the whole balancer

You say the bolt is tight? then if that is the case the balancer out ring is comming apart, the balancer needs to be replaced