1941 ulh heads

[T. Cotten]

Actually, those holes likely were for balancing. Many people forget the early u motors used an open female rod, which is substantially lighter than a later closed set..

But the bottom of the rods, Chuck,..

Is designated rotating weight;
You balance to a percentage of the reciprocating mass.

The tops of male and female rods are essentially the same.

....Cotten

[chuckthebeatertruck]

But the bottom of the rods, Chuck,..

Is designated rotating weight;
You balance to a percentage of the reciprocating mass.

The tops of male and female rods are essentially the same.

....Cotten

This reply has me confused as it implies there is no reason to weigh the rotating weight.


Every balance sheet I've used has one weighing the rotating mass and adding that weight to a percentage of the reciprocating weight to figure the bob weight.

This implies that a change in rotating mass does affect the overall balance.

I like to work with theoretical models vs. words for something like this to make sure we are saying and meaning the same thing(s).

So, here's my crusty attempt:

If the reciprocating is steady at a generic 1600 grams then 55% of that would be 880 grams [1600 X .55]

If the rotating mass were (for the sake of this example) 1500 grams with an open rod and 1600 grams with a closed rod (yes, I know the spread is not this extreme) then we'd have total weights of 2380 for the open rod [1500 +880] and 2480 [1600 + 880] for the closed rod. Divided by two means we have a 50 gram spread on each wheel between the weights calculated for the open and closed rod.

Whilst the motor may never care about that 50 gram per wheel difference . . . the balancing job does.

Put simply; a lighter bob weight = more mass taken out of the far side of the wheels to "balance" it. Conversely, a heavier bob weight may not need any mass removed from the wheel.

I'm open to learning -- so, what am I missing?

[T. Cotten]

This reply has me confused as it implies there is no reason to weigh the rotating weight...

Exactly, Chuck!

The rotating weight only becomes necessary when dealing with multiple-throw motors.
(Because ya gotta fake it with bob weights..)

If you know your reciprocating weight on a v-twin, even though the flywheels are assembled, you can still static balance it to any percentage you dream up.

People make more out of it than it is.

....Cotten

[chuckthebeatertruck]

Ah, now it becomes clear.

I get where you are coming from Cotten and I don't disagree.

However, I think we are talking past one another instead of with one another.

I was and still am responding to the original poster's question, which stated in sum: why are there all these holes in my flywheel?

I am not responding to "what balance factor should I use" . . . nor entering into a balancing discussion.


I gave a plausible explanation to the OP for why his wheels "may" have more holes than expected.

This explanation is rooted in the understanding of how many people balance wheels . . .and how a change in the rotating mass affects the bob weight calculation, which can and does directly affect how many holes are drilled.

In this regard, I think we can both agree there are many motor builders over the generations who have not yet evolved to your level of understanding regarding balancing. As a result, they have spent quite a bit of time balancing their v-twins searching for something. Put simply, we do not know who last worked on the OPs wheels nor where they stood on balancing. We are only left with context and guesses from that context.

When I thought this through; the general contexts I applied were as follows:
how common is balancing -- pretty common.

How common are holes drilled to affect balance -- pretty common.

How does a lighter rod affect balance -- generally more weight comes out of the wheel. Put all that together . . .

And, I stand by my statement that the most likely reason for all the holes in the OPs wheels are for balancing and that it is entirely possible the wheels were balanced for lighter, open female rods which could result in more holes in the wheels than the OP is used to seeing in other v-twin motors.

May we please respond to this guess ^^^^

Otherwise, we aren't talking with one another -- we are talking AT one another; which is little help to the OP or us.

[T. Cotten]

I didn't say they weren't balancing holes, Chuck!

That's usually their intention, whether right or wrong.

I just picked at your open female rod thing.
The top of an open female rod only "weighs" less than the top of a closed rod.
(Because its "half" of a lighter rod.)

If you whacked them off with a chop saw, they would be the same mass.

Really don't need no bobweights, really: Balance the real assembly.

And you don't need to drill the wheels at all, if you can lighten the reciprocating hardware.
Pistons are temporary, not the wheels... Or plug existing holes.

....Cotten