There's been lots of debate in this forum about whether or not the crank pulley is also a harmonic balancer. I've been told by my Nissan dealer that it is a balancer and also by close mechanic friend. The Chilton's manual refers to it as a balancer too. What do you think it is?

Since many people are now running underdrive and light weight crank pulleys, do you think they run the possible chance of a crank failure without the balancer (if it is a balancer)?


Dave

 

Here's one thing to consider aside from the harmonic balancer debate.

Imagine your looking at the crank assembly from the side. You have a big, heavy clutch or torque converter hanging off one end of the crank. On the other end of the crank you have the crank pulley. To me, it seems Nissan must have designed that pulley to be a certain weight on purpose. I mean, why else would they make a 8 lb or whatever pulley when they could just as easily make it 1/4 that weight. It just seems to me that the UD pulley would make the crank "back heavy" and alter the loads on not only the front and rear main bearings, but possibly affect harmonics.

I removed my UD pulley after ~1 year because the thought just frightened me too much.

You used to be able to do a search at The Old One's site; there had been loads of discussions regarding this topic. It appears that BBS is now defunct, but I was able to find one archived post from The Old One regarding at least one of the uses of a heavy factory crank pulley (note that the Honda type he discusses is the SAME type used on the Maxima):
http://www.theoldone.com/archive/pul...n_balancer.htm

 

I'll answer because you called out my name in the Post Subject line. Warning: this response is more in the "I think" category than the "I know" category. If other forum contributors have knowledge of the subject, please join in the discussion.

Harmonic Balancer is a misnomer. What is often called Harmonic Balancer is really a Harmonic Damper. Nissan doesn't use either term; the factory service manual identifies the part as Crankshaft Pulley.

The venerable Chevy small block V8 engine was made in a variety of displacements including 265, 283, 302, 305, 307, 327, 350, and 400 cubic inches. The 400 version could not fit normal crankshaft counterweights within the engine block skirt. Engine balance was achieved by adding balance weights to the flywheel and crankshaft pulley. In this unusual engine the crank pulley truly deserved the name "balancer".

The main purpose of a harmonic damper is to control harmonic vibration, not to balance the engine's rotating assembly. An underdrive pulley has a smaller diameter for the drive belt, but is not necessarily lighter. The advantage of an underdrive pulley is that it reduces the parasitic loads (alternator, P/S pump, A/C compressor) by turning them at lower rpm.

I'm not familiar with a lightweight crank pulley. Such a part might be useful to the all-out racer, the fellow who would also install a lightweight flywheel. I can't imagine that a lightweight crank pulley could provide much benefit, given the small diameter of the part.

For general information about Harmonic Dampers, go to http://www.fluidampr.com/problem.html

 

I checked the Stillen on-line catalog.

The description of their 4Gen underdrive pulley #408240 does not mention weight. Presumably its weight is similar to the stock unit.

The description of their 4Gen aluminum flywheel #451065 includes this claim:<font color='blue'>
"This billet aluminum flywheel is just over half the weight of the stock iron unit. With reduced weight (stock is 17.5#, this beauty weighs in at just over 13#), less power is needed to overcome flywheel inertia."</font>

I can't see how "just over 13#" can be regarded as "just over half the weight of the stock iron unit." Okay, let's cut them some slack, and assume they didn't mean weight, they really meant angular inertia. According to http://library.thinkquest.org/16600/...linertia.shtml the formula for the moment of inertia of a disk spinning about its central axis is I = 0.5xMxR*2. Is the radius of the Stillen flywheel less than the stock piece? I doubt it, because the ring gear on the periphery of the flywheel has to engage the starter pinion.

Given the simplifying assumption that both flywheels are plain disks of equal diameter, the angular inertia is proportional to the mass. Is Stillen blowing smoke, or is there more to the story?

 

hehehe............Sorry Dan.......Couldn,t resist!!

 

For the person that said the UD pulley isn't necessarily lighter.. it has to be. First of all going to the basics. If the stock underdrive pulley is made of steel and there is another identical one made of aluminum, the aluminum is undoubtabely gonna be lighter. Besides being smaller, it is also lighter.
Ex: for my friends 300ZX TT. Stock is about 8-12 lbs (can't remember exact weight) the billet aluminum UD Pulley weighs 3 lbs.
Being that it is smaller, and lighter, it takes less power from the engine to drive all the belts.

 

At a constant engine speed, weight has no effect. Weight (mass) is a factor only for changes in rotating speed (acceleration).

If one looks at the site DBM refers to, it should be observed that the equation he has is for angular momentum. If you look at the one for kenetic energy, you'll see that the value for angular velocity (omega) is squared. So: differences in rotating mass have much greater effects at high velocities than low one. Again, this is only a factor for changes in velocity (acceleration).