Flywheel Balance Factor for VL Motor

[Buster]

Can anybody (or Steve) tell me what the factory flywheel balance factor should be for a stock VL motor. I know about 50-60% factors for later motors, but I have read several places the stock VL motor has a flywheel balance factor in the 40%'s. If so, why so much difference and what is the factor. Thanks!!

[harleytoprock]

I don't see why a 60% factor wouldn't work very good on a VL. It's been proven to be good for late motors. The reciprocating motion isn't any different between early and late motors. Maybe back in the 30's the factory didn't know any better. I'd also like to hear what other people have to say about this.

[sswaney]

If you do a search for "harley balance factors" there was a good discussion on this site back in 05. Its worth the read.

[Steve Slocombe]

I've been using a 46% balance factor on my last dozen VL motor builds and they seem fine. This came from my flywheel balancing guy about 15 years ago who said he found it in a notebook. He said the more modern Harley motors were balanced 58-60% as they were meant to blat around town at low revs. Most of the old books seem to imply 50% balance facors as they talk about halving weights when calculating for balance. It can't be that critical, as Shop Dope 112 of 17 December 1934 says it is not altogether necessary to rebalance flywheels when changing from iron pistons to the new T-slot aluminium pistons, as long as both pistons are changed. Those big VL flywheels must be very forgiving.

[Kozy]

How do VL flywheels compare to UL flywheels in regard to mass?

[Rubone]

Very comparable, the physical dimensions are almost identical.

[T. Cotten]

Harleytoprock!

The reason for the lower factor for Vs is the different mounting within the frame.

Kozy!

Factor is totally independent of total mass.
Heavy wheels and light wheels can have the same factor.

The real shame Folks,..

..is that nobody takes the time to back-calculate unmolested motors before they molest them. Thus choice of factor is nearly always based upon hearsay or blind conjuring.

Fortunately, V-twins are enormously forgiving!

....Cotten

[Buster]

I am building a fixture with parrell sharp edge bars (similar to what Cotton shows at Virtual Indian site) to static time the assembled flywheels. Current balance holes at heavy end of flywheel are drilled from interior of flywheel. If I have to drill additional holes, can they be drilled from exterior of flywheels as long as they do not line up with current holes on interior sides. My flywheels currently have two drilled holes on one flywheel and one drilled hole on the other flywheel. If factor is below 50% (say 46%) would not the weighted end of the flywheels be lighter than the measured recipricating + rotating assembly. I do not have OEM pistons and will be using after market pistons. To static the assembled flywheel assembly on my parrell bar fixture, whould not I have to temporarily add weights to the heavier counter weighted area of the flywheels. I am over my head, but I am going to learn how to do this. Thanks!!

[harleytoprock]

You should balance the wheels seperately.

[T. Cotten]

Buster!

I'm not clear on your question, but first,..
"knife edges" aren't really 'sharp', but ground to a narrow flat on top.
If I were to do it again, I would just use ground round stock instead of ground planer blades.

The flywheels won't know if you drill all the way through to another hole.

And most factory-mated wheels are already "equalized" satisfactorily. Balancing them separately is often an exercise in feeling good. You hope they are moving as one mass anyway!

When on edges, you will be stacking weight upon the rods (or conjuring a bobweight) to simulate the reciprocating mass, until it comes to balance. Then you can calculate the existing factor, and stew about changing it.

There is only one total reciprocating mass in the motor balancing formula, and only one counterbalance mass. The percentage of the total reciprocating mass that brings it to balance is your factor.

So you need to know your total. Weighing the piston assemblies is easy.
The rod tops only take a little more attention.
This can be achieved, even while assembled, as shown in the attachment.

....Cotten

[Kozy]

Model U ballance factor

Harleytoprock!

The reason for the lower factor for Vs is the different mounting within the frame.

Kozy!

Factor is totally independent of total mass.
Heavy wheels and light wheels can have the same factor.

The real shame Folks,..

..is that nobody takes the time to back-calculate unmolested motors before they molest them. Thus choice of factor is nearly always based upon hearsay or blind conjuring.

Fortunately, V-twins are enormously forgiving!

....Cotten

Cotton,
I'm not a machinist or a engine builder so I don't know all the things that effect selection of balance factor. All I know is what I've heard and the low factor for the VL surprised me. I read your compilation of posts at the VI site and now realize a factor for a particular VL motor would not necessarily work for a particular U motor even though the motors are similar. That being said, can you give me an idea of acceptable range of balance factor for a U in a stock chassis? Have you ever had the opportunity to back calculate a U to determine OEM factor?

[harleytoprock]

"And most factory-mated wheels are already "equalized" satisfactorily. Balancing them separately is often an exercise in feeling good. You hope they are moving as one mass anyway!"
I repectfully disagree with you on that one. First there is no guarantee the wheel are equalized to begin with. Next material removal could throw off equalization even if it was right from the start..
Only time I would balance as an assembly would be if dynamicaly balanced. One wheel could be out and the other wheel also out to compensate, yet when staticly balancing the assembly, it could show correct balance.

[T. Cotten]

Harleytoprock!

Which part do you disagree with?

"Most"?
(..or "satisfactorily"? I'm getting uncomfortable with the spelling myself.)

And what keeps you from drilling the two wheels equally?

For that matter, what keeps you from adjusting the reciprocating weight, and not touching the wheels at all?

....Cotten

[Buster]

Hey Cotton, do you static balance harley flywheels as an assembly or balance them seperately? Uncle Frank's Q&A says to balance harley flywheels sperately. If this is true why are Indian flywheels balanced as an assembly and harley flywheels balanced individually. I appreciate everybody's comments.

[T. Cotten]

Kozy asked: "...can you give me an idea of acceptable range of balance factor for a U in a stock chassis? Have you ever had the opportunity to back calculate a U to determine OEM factor?"

I've never been trusted with a U that hadn't been molested, so it is up to others to save what History comes by them.
As far as an 'acceptible' range, I can only guess the range is so wide that it would be hard to pick a bad one.

V-twins are incredibly forgiving, unlike opposed or inline designs.
The motor doesn't even care if its pistons match.
And an ideal factor for one application may not be ideal for another, such as solo vs. hack, but both will run fine with the other's factor.
My belief, based upon personal experience alone, is that choice of factor is a tuning tool, that can give identical motors of differing factor different characters of performance.

And Buster asked: "...do you static balance harley flywheels as an assembly or balance them seperately? "

I don't accept motorwork any more.
But when I did, every motor was different, be it miss-matched swapmeet refugees, fresh T&O's, or somebody's previous excursion into fantasy balancing. My own Chief came with one cast wheel, and one Z.
My experience upon a Stewart-Warner machine tells me that dynamic balancing has its time and place too, but predominately in the later third of the Century!

Basic balancing technique does not distinquish between marques.

As far as re-balancing mated wheels, I never hesitated to do them assembled.

Let us ponder, Folks,..
Just how flywheels were treated at the factory. Raw wheels probably came from the foundry in batches. Undoubtedly they were machined in batches as well. My best suspicion is that sample wheels were balanced and averaged, and then the "floor" was told to where to drill just so many holes, just so deep, for that batch. Voila: "balanced".

As I posted, one must 'stew' over one's choice of factor, and knowing what it is to begin with often makes decisions easier.

...Cotten