andrew383

iTrader: (14)

oh come on guys help me out

Yogi Bear

We're talking about 2 types of balancing here. When you take your crank, pistons and rods, and have them "balanced", you are balancing the rotating masses. The shop will weigh the pistons and rods to come up with a combined weight. The shop then installs "bob weights" on each crank pin journal which are equal to the measured combined weight of the pistons and rods. The crank is then spun on a lathe like machine to check for balance, much as the guys at the tire store spin your wheels & tires to check them for balance. After taking balance measurements (vibration) while spinning the crank, the operator stops the crank and adds or removes metal at the counterweights to balance the crank. A crank that spins with bob weights attached without vibrating is said to be "balanced". The LS motors are "balanced internally" because no weight on the flywheel or the front pulley is used to balance the rotating assembly. Some Ford V8s were externally balanced because they used offset weight in the flywheel to achieve rotating balance.

The harmonic balancer on the front of the crankshaft serves a completely different purpose. The harmonic balancer or "damper" damps out the TORSIONAL VIBRATIONS. As the crank spins, the pistons and rods transmit impulses to the crank, much like striking a spring with a hammer. The combustion impulses twist the crank with alternating positive and negative forces. These impulses make the crank vibrate in the torsional direction, like a clock spring ticking back and forth. If these torsional vibrations are at just the right frequency (RPM) they will cause excessive stress on the crankshaft, eventually leading to catastrophic failure.

What is needed is a damper or shock absorber, to damp the torsional vibration. This is where the harmonic balancer or damper comes in. The damper is constructed of 2 concentric pulleys with a gap in between. The gap is filled with rubber. When the crank tries to vibrate torsionally The force of the vibration is damped (absorbed) by the rubber ring.

Have you ever bounced on the bumper of a car or truck with no shocks? The car continues to bounce long after you get off because there is nothing but a little friction to stop it. Install some good shocks on the car, and the car only bounces as long as you bounce on the bumper. The shocks are damping (absorbing) the energy, and stopping the vibration.

A harmonic balancer does the same thing to a crankshaft that wants to vibrate in the torsional direction. The balancer absorbs energy and prevents torsional vibration. A crankshaft without a harmonic balancer will fail much sooner than one with a balancer. If the UDP is not a balancer, you are asking for trouble.

andrew383

iTrader: (14)

so it wouldnt send the vib's through the pulley to the belt then?

LMSeven

iTrader: (3)

Dude just buy the god damn pulley

andrew383

iTrader: (14)

dude read the gd thread!!! i already bought it.look at the first 2 posts i made its my car its on

Yogi Bear

We're talking about very small torsional vibrations here. You have very large forces moving through very small angles. A crankshaft is quite stiff, and won't twist very far. The vibrations would be damped by the rubber ring in the damper, and little, if any, would be transmitted to the belt. The stretch in the belt would further damp the vibrations so that they would be inconsequential. You get much more vibration in the belt from the impulses created by the A/C compressor.

andrew383

iTrader: (14)

so would everybody say to just take it off? or keep it on?

Yogi Bear

It depends on how much of a gambler you are. Chuckie, in post #7, has had good luck with his for 130,000 miles. It's a crapshoot. I wouldn't want to take the chance on breaking my crank for a measley 5-6 HP.

LMSeven

iTrader: (3)

My bad I missed the 2nd post, I was drinking last night (longest 3 days of work ever). Lots of people run them, lots don't. Making horse power isn't always safe!

andrew383

iTrader: (14)

ah its cool