How to balance a flywheel?

[Steve Jelf]

A triple gear seized and spun the pin, and wallowed out the hole, so the flywheel is toast. When I have the magnets on the "new" flywheel and it's ready to install, I'll need to balance it. I would really prefer not to undo all the caps and rods and remove the crank shaft from the engine. If I sandwich the flywheel between two transmission shafts, bolt them together, and put the works on the balancer, will that be good enough, or is there likely to be too much runout in the shafts?

[speedytinc]

If your shaft bases are square you will not have a problem.
This is how I do it.

[Harry Lillo]

If you are satisfied that your crankshaft is balanced properly,
independent of the flywheel assembly you could do so.
Mine are usually balanced as a unit and are indexed to
go together the same way.
Harry

[JTT3]

Steve you would need to make sure that both transmission shafts are straight first. Then balance that assembly first. Index bolts to the shafts & flywheel for fit and location. If you’re lucky enough to have a static balance set up it will be much better.
I have remove material from the the edge & face of the flywheel proper, I can’t find it now but I have a chart that shows the weight of material by hole & depth size that will give you an idea of weight removed. I do capture the material drilled out and weight it on a digital scale to confirm. I determine the balance using disk magnets that you can buy at hobby lobby. These can be located on the flywheel to bring the flywheel into balance. They come in packs that have several sizes of magnets. You’ll need to weigh them each so you’ll know how much material needs to be removed or added. Hope that helps

[Craig Leach]

I hate to say this but harbor freight sells a motor cycle wheel balancer that may be of use for this.
Craig.

[Erik Barrett]

I balance flywheel or flywheel/magneto assemblies using two transmission main shafts end to end for a mandrel. I make sure to offset the key slots for the clutch hub 180 degrees apart. Then the unit is static balanced on precision leveled knife edges. This procedure is accurate far beyond what is needed for a model T. In fact I sent one of my static balanced units out to be spun on a dynamic balancer at a speed shop. It came back with two 1/4” holes drilled about 1/8” deep to zero it out. I also made mandrels to balance the transmission drums on the same rig. They are much more difficult to deal with.

[Allan]

Eric does as I do, except my "precision" edges are ground down back edges on 14" hacksaw blades. It is easy to determine the heavy spot and have at it with a 5/8" drill in my drill press. The hardest part is repeating the drill/balance/drlll a bit more/ balance cycle until the heavy spot goes away. I too had one of my own primitive jobs balanced by a machine shop, with just a smidgeon more in one hole, "just because we could" was their verdict.

Allan from down under.

[dykker5502]

Well, a flywheel is a wheel like any other whell I presume so I have twice with great succes balanced a model T flywheel with magnets and all on a regular wheel balancing rig:

The cone on the axle ensured that the flywheel was centered but I had to measure for a little tendency to wobling, but a hit with a rubberhammer could get it right. Just to be sure I checked both axis:

Initially it was quite out of balance!

It shows where to put the balancing weight. Well, we can't do that, so we have to remove that weight from the direct opposite place
So how much steel to remove for 62 grams? Well, drill and meassure, drill amd meassure and at last it's OK:

You can see the final turn here (Youtube video).
And the final result here:

"OK" means it's within +/- 2 grams.
I have since assembled the engine and put it in the car and driven it - it goes like a Rolls-Royce

Theoretically you can do both a static and dynamic balancing on a rig like this and I have done it on a 1926 Chevrolet flywheel, but it requires a certain thickness like a regular wheel, and since model T flywheels are so relatively thin, only static balancing is done here.

[jab35]

Just curious, Steve:

What was the clearance of the triple gear bushing to pin diameters when you assembled that transmission? Also, IIRC you had media blasted some parts for this rebuild, were the pins, by chance, old ones sandblasted and reused? Thanks, jb

[Charlie B in N.J.]

Man I love that dynamic balancer set up. There’s no way you can get any closer.

[J and M Machine]

'Quote" If I sandwich the flywheel between two transmission shafts, bolt them together, and put the works on the balancer, will that be good enough, or is there likely to be too much runout in the shafts.

Yes You can get away with this to get it close but right way is to have it dynamically spun on a balancing machine.
I have posted pictures of most likely worst Model T flywheel we balanced showing significant unbalance of flywheel assembly.
I individually weigh the triple gears and then weight match them to each other.

[BobShirleyAtlantaTx]

If you have a lathe or a friend with one it easy to make brass thimbles of any weight needed. If you need a lot of weight they can have straight sides.

[BobShirleyAtlantaTx]

That way no permanent change is made to the flywheel.

[dykker5502]

Oh, I forgot to mention that I weight the 3 triple gears and eventually take a tiny bit off in a lathe on the two that are heavier than the lightest. I believe J&M machine do the same if I understood them right.

[Allan]

John's photo of the non starter flywheel is not like any Ford flywheel I have seen. Balance boring on the outer edge of the flywheel is not usual. The flywheels are balanced PRIOR to fitting the magnets on starter flywheels, as the boring registers are under the magnets. You can imagine how well that works when 16 heavy magnets and ancillary fixings are added. Often the balancing holes drilled on an assembled flywheel are in completely different positions to the factory ones.

Allan from down under.

[RajoRacer]

It's a very early flywheel with those type of magnet bars.

I also use a Sunstrand static balancer.

[Steve Jelf]

What was the clearance of the triple gear bushing to pin diameters when you assembled that transmission?

Wish I knew. I didn't do them, and I didn't think to ask.