Flywheel imbalance

[wolf k]

All good stuff.
Anybody know why Ford changed from 28 oz. to 50 oz. on the same sized engine, 302?

[Jerry Clayton]

Post #10---first picture---thats an ATI hub and weight for an Ford 302---the weight bolts on--stock OEM weight is cast as part of the hub

Keep in mind that there are a lot of drive line harnmonics in different gears, angle of u joints as suspension goes thru ride height changes, etc that the dampner also cancels out---all harmonics don't come from strictly engine vibes--------

[Caprimaniac]

The balance/ imbalance, crank balancing and crankshaft balancer topic is coming together, then... (Very easy to mix them up!)

Sorry for hijacking the thread.. but... been thinking of this for some time:

Jerry, or anyone with insight on the topic, do you have any input on weight of balancer? Take ATI as an example. They have steel, steel aluminium and all aluminium dampers. Weight of alu dampers are roughly 1/2 of the steel ones.

On a performance engine turning 7- 8000 rpms with "good" , balanced, internals would you see any downsides of using a lightweight aluminium balancer?

My thoughts are: With a heavier the outer ring of the balancer the smaller the tendency for the crankshaft to bend or twist at speed. But, if hard accelerating or braking, a greater twisting force applied by the heavy weight balancer.
Also: Are the heavy balancer a trick from the thoughts of having a steady idle and low rpm torque? (Likewise for a heavy flyywheel.)

RS

[blykins]

I would use an all-aluminum balancer in a 100% full-race application only, where weight savings is paramount. Aluminum is light, but it's not as capable of absorbing torsional harmonics as well as a steel or steel/aluminum piece.

[xb-60]

....and is there a relationship between the mass/diameter of the flywheel (and clutch?) and the mass/diameter of the harmonic balancer? I take it you don't just go and buy just any harmonic balancer for a zero balanced engine, it has to be matched?
Cheers,
Glen

[blykins]

If its internally balanced you buy any 0 bal flywheel and any 0 bal harmonic balancer.

[MOTORHEAD]

While searching for the proper damper for my 428 cranked fe I've noticed several
references to " zero balanced @ 28 oz".which seems like an oxymoron to me. How can it be zero balanced ,but have a 28oz weight in one place ? Obviously I don't understand the term. @

[blykins]

It's because a 410/428 FE is an odd-duck....

All FE's have a 0 balance harmonic balancer, but 410's and 428's have a 28oz weighted flywheel/flexplate.

[tirod]

On most engines seeing rpms under 6500, it's cost effective to just run what the factory did.

What a lot of race engine builders do, and how it's trickled down to the street, has been distorted over the last 45 years. Sure, a properly balanced engine runs smoother, and that's the first clue - owner comfort. Driving a buzz box doesn't connote quality. It's why some four cylinders are fitted with balancer shafts to reduce the vibration. BUT - those smoothly running motors are no guarantee of vastly improved longevity. They wear out just the same; some, like the 2.5 Chrysler, don't even last that long. (Sure, ask me how I know.)

There's another thing going on in the crankcase most don't know about. All the oil slinging around isn't formulated to be that slick, it has a tendency to cling. What good is it if it runs off immediately? It needs to stay there and keep doing it's job, providing a place for metal to spin separated from the other metals.

Smokey Yunick took photos of that back in the '60's - it's in his book Power Secrets, and it shows a crank at speed with about two quarts of oil wrapped around it in a disgusting blob. And - it wasn't smoothed out, it has heavy places that move around.

How can your crank be balanced with over 16 oz of oil floating around on it knocking it out of balance? ITS NOT BALANCED. And that's why the harmonic balancer is there to smooth out all those randomly occurring vibrations.

Go look up racing pans and windage trays, what's the one thing many race cars use? Crank scrapers and strippers, fitted within thousandths of an inch to clean off all that oil and 1) return it to the oil pickup, 2) reduce the rotational inertia. Look around some more and you'll see vendors selling coatings for the crank throws and rods that help sling off oil that sticks to them.

Guys, we've been getting sold high precision balancing jobs for over 40 years, but when you get to actually talk to a machinist in a shop building his own, he puts it together with the factory balance - and tolerance, which is good enough for any stock crank.

It's just another high speed low drag things that consume cubic dollars in an otherwise warmed over stock rebuild, and a lot the myth about it is overblown. If you're not running a crank scraper, your engine simply will not ever be completely balanced while running, and the money was wasted.

[Caprimaniac]

Originally Posted by blykins

I would use an all-aluminum balancer in a 100% full-race application only, where weight savings is paramount. Aluminum is light, but it's not as capable of absorbing torsional harmonics as well as a steel or steel/aluminum piece.

That was my thoughts as well.
And some folks say the heavy balancers will kill the crank for instance in dragracing where the RPM's go from 9000 to 1000 in an instant when going off the throttle or from 4000 to 9000 at launch....

"....and is there a relationship between the mass/diameter of the flywheel (and clutch?) and the mass/diameter of the harmonic balancer?"

Add diameter = add mass.
But; the diameter has nothing to do with the flywheel/ balancer imbalance.
For instance in small Cheby (and Ford?) you have 6 and 7" diameter balancers. Not only are the 7" heavier if width & material is the same, but having the mass at a greater distance from the centre makes higher momentum, and therby higher force.

You see racing clutch- setups are twin or tripple 7" and some circletrack (and also cup- cars? And drag- cars?) run without any harmonic balancer.....

[xb-60]

Originally Posted by tirod

... it shows a crank at speed with about two quarts of oil wrapped around it in a disgusting blob....

tirod – surely what shows in the photos is the oil cloud? I didn’t know what a windage tray or a crank scraper is, so did a bit of looking around. Doesn’t the windage tray attempt to control or limit the oil cloud, which when not controlled, provides resistance to the rotating assembly? It seems that when done correctly, a windage tray can contribute to a power improvement of around 3%.
Cheers,
Glen

[xb-60]

[quote=Caprimaniac;1199242]
"....and is there a relationship between the mass/diameter of the flywheel (and clutch?) and the mass/diameter of the harmonic balancer?"

...Add diameter = add mass....[quote]

That’s true of course. But if I’ve understood correctly, both the flywheel/clutch combo, and the harmonic balancer are responsible for absorbing the harmonics, or resonances, that result from multi-sourced vibrations. Some of the resonances come from the torque transferred to the crank from each piston after combustion. So...it would seem logical that you don’t just slap on any convenient (zero balanced) harmonic balancer, as the HB and the flywheel need to work as a pair, so need to be sized to complement each other. IMO.... but really I’m just guessing, which is why I’m asking....
Cheers,
Glen

[Caprimaniac]

...."as the HB and the flywheel need to work as a pair, so need to be sized to complement each other"

We've agreed that both need the same imbalance or lack off such, so that's a sealed topic.

Regarding to total weight or physical size (diameter) I would say, it depends.
A lightweight flywheel/ clutch and a very heavy harmonic balancer or vice/versa- might not work out very well. I've never looked into it. It's interesting topic, though....

For instance; Should you put flywheel + clutch assembly on the scales and find a HB with approx same weight?

As I understand it, only the HB will absorb the harmonics/ resonances. (In addition to the rotating mass itself, down to the molecular scale...)

As the both serves as rotating mass at each end of a rotating stick, I suppose you are right that this also might take up some, in itself.

The imbalance in the rotating front and rears are there to minimize harmonics, so that's another story.

[xb-60]

Originally Posted by Caprimaniac

...A lightweight flywheel/ clutch and a very heavy harmonic balancer or vice/versa- might not work out very well....

Anybody know what the story is? Plenty of people - from what I've read in this forum - go to a lightened flywheel and clutch for racing, so what do they do with the HB? Go lighter? Go heavier? Cross their fingers? Is there a relationship or rule that you use?
Cheers,
Glen