Harmonic Balancer

[Fraze]

Advice needed! Both my FC and an FB engine I have, have a disc of approx.170mm dia. riveted onto the front of the pulley. I have a new "Powerbond)" harmonic balancer which is supposed to suit all grey motors but it does not have the disc, but does have three tapped holes in it (may be for jacking screws??). I would rather use the new harmonic balancer- but how important is the disc? Thanks Frazer

[Harv]

G'day Frazer,

The disc is part of the old balancer... it comes off with the steel hub, then you throw the lot away and put on the new PowerBond balancer.

The original GMH grey motor harmonic balancers have a central hole which is tapped to 1 1/8” UNF (to accept the harmonic balancer puller tool - you need to buy or borrow one to get it off). However, the aftermarket grey motor harmonic balancers available from PowerBond have no central tapped holw. Instead, they use the three concentric bolt holes tapped through the hub to 3/8-24UNF on a 2 13/16” (71.44mm) PCD. These will come off with a "SuperCheap" type harmonic puller.

Cheers,
Harv

[Fraze]

Thanks Harv, you have confirmed what I suspected, but it is always wise to seek advice when unsure. Cheers, Frazer

[ardiesse]

Fraze,

Aftermarket grey motor harmonic balancers are to the same basic design as the red/blue/black motor harmonic balancers, but dimensioned to suit the grey crankshaft and timing case oil seal.  So even though they look nothing like the original balancer, they are a direct replacement.

In the original equipment grey motor balancers, the disc is the "inertial" component.  Two pieces of rubber sandwich it between the pulley and the hub.  The rubber is there to provide damping of torsional vibrations - the disc "wants" to resist sudden changes in speed, and the rubber has a little give in it to allow this to happen.

In the red/aftermarket grey balancers, there's a rubber ring between the hub and the pulley.  The pulley is quite heavy, and does the same job as the disc above - the rubber ring it rides on has a bit of give.

In short: both styles of balancer work on the same principle, but look completely different.

Have I gone too technical?

Remove the old one, replace it with the new one.  Job done.

[hsv-001]

Was the original a heavier unit ? Haydn

[ardiesse]

Haydn,

I'm going off on a tangent in this post.

I'm not certain the earlier version would have been heavier.  Can someone weigh an example of each harmonic balancer?

My hunch is that Holden harmonic balancers, of whatever design, are completely inadequate at their intended task.  Because: the grey motor 6200 rpm no-go zone.  If the balancer had been correctly designed, the 6200 rpm no-go zone would not exist.

Read on at own risk -

Harmonic balancer design is basically a black art.  It would most likely take a few broken crankshafts in the course of getting all the parameters right.  (These days, with a good finite-element analysis software package you'd stand a half-way decent chance of getting it right without breaking any cranks.)

Torsional vibrations in the crankshaft end up getting absorbed in the rubber component of the balancer.  The rubber is "springy", but not perfectly so, and the dissipative property of the rubber is crucial.

Things are complicated a little by the fact that the whole thing spins at engine speed, which is why a harmonic balancer has to have an inertial component in it, just like a little flywheel.  The important quantity here is the moment of inertia of the rubber-damped component - the higher the better. (Tries to remember first-year physics) For a point mass, a ring, or a thin-walled cylinder, the moment of inertia is mass times radius squared. For a disc, the moment of inertia is mass times radius squared, divided by 4.  The original balancer more closely approximates a disc.  The aftermarket balancer more closely approximates a ring.  The aftermarket balancer, then, makes more efficient use of the available mass.  But there's a lot more going on . . .

The engine's crankshaft and flywheel make a resonant system, much like if you clamp the end of a steel rule in a vice, and pull and release the free end.  It vibrates at a certain natural frequency, which in a grey motor occurs at 6200 rpm, so I'm guessing 103 hertz.

At resonance, the flywheel end of the crank is the point of maximum stress, which is why the cranks in racing grey motors break the flywheels off at 6200 rpm.  The harmonic balancer is at the front end of the crank, where the amplitude of vibration is maximum.

The designer's job is to fiddle all the parameters, like the lossiness of the rubber, its thickness, width, depth, and its radial position from the axis - so that all the vibrational energy in the crankshaft at resonance is transferred into the rubber, where it is converted to heat.  And the resonance is gone, damped out stone-dead.

It's the same class of problem as designing a matched load for a quarter-wave transmission line resonator in radio electronics (which is my day job).  Which means - with the right test equipment, you can measure the system and determine how well your harmonic balancer damps torsional vibrations, and not by the gloriously hit-and-miss method of revving an engine through 6200 rpm and seeing whether any bits come flying off either.

Now, if I had a few weeks of long service leave, a spare motor, some piezo transducers and a machine shop . . .

Rob

[Fraze]

I like your observations Ardiesse. My son used to race HQ Holdens years ago and at one meeting at Bathurst the flywheel bolts sheared on a fresh engine after only a couple of practise laps. The engine builder replaced these and the same thing happened again next practise. The engine man then realised he had replaced the harmonic balancer with a super doper after market one. This came off and was replaced with a standard GM unit - exit problem! Frazer

[Fraze]

Haydn, I weighed the harmonic balancers on the bathroom scales (which are notorious liars) and the old unit with the disc weighs 1.9kg and the new Powerbond unit weighs 1.7kg, Frazer

[hsv-001]

Ah ,I had a feeling the after market ones were lighter .Just through letting the clutch out under load . Regarding these old motors turning into grenades at revs . An old boss told me that to rev them you had to take as much as possible off the flywheel ,he was building speed cars pulling weight wasn't an issue  .Haydn

[Professor Grey]

Once upon a time I read in a couple of threads that the old style harmonic balancers were superior to the modern type.
Someone people said that a harmonic balancer from a Ferguson tractor was the best, because it had a larger diameter.
I'd be interested to see some discussion on this.
Cheers,
Prof.

[fcee]

  How is the aftermarket balancer installed without damage if you cannot use the old installing tool ? also has anyone heard of fitting a mercuy filled tractor balancer ,supposed to be the best of all . cheers  Steve.

[Harv]

How is the aftermarket balancer installed without damage if you cannot use the old installing tool ?

The new ones fit up by easing the balancer onto the shaft (like the old one), then using either a brass drift, large socket or small lump of wood to spread the load as you gently tap them on. Best to use a little BFH  .

Cheers,
Harv

[GreyFC]

I have a Ross Harmonic balancer:

http://rossperformanceparts.com/harmonic_balancers.html

There are 4kg.  Much Much bigger then the standard or the aftermarket redmotor type.

Anything to reduce the wobbles is an option I'll take.

[GreyFC]

  ....also has anyone heard of fitting a mercuy filled tractor balancer ,supposed to be the best of all . cheers  Steve.

Yes.  This was common.  Now days impossible to get one.

I tracked one down that had a slip for a red motor.  By Chance he lives close to me but the price was excessive.

Here are 2 pictures:

[Harv]

Yes.  This was common.  Now days impossible to get one.

I tracked one down that had a slip for a red motor.  By Chance he lives close to me but the price was excessive.

Mercury ones are hard to get, but Fluidamper still make the fluid filled ones (albeit with some more modern silicon based fluid). Would need to be a custom jobbie though:
http://www.fluidampr.com//

Cheers,
Harv

[fcee]

how do you know when to replace a balancer ? is it likely that an original would be degraded in the rubber enough to need replacing ? thanks Steve