Scout Balance Factor

[T. Cotten]

If you have the patience and math skills, CB,...

The goofy little S&S stand could still be used with your custom arbor, but it makes it all really really tedious.

Are you equipt to weigh your rod tops and bottoms, and conjure bobweights?

....Cotten
PS: I got talked into an S&S HD arbor, if anybody thinks they need one cheap.

PPS: The pic of the rails is from a 1942 Quartermaster Corps handbook, TM-515, digitized by google from the University of California.

[T. Cotten]

This drawing really bugs me, Folks,..

Engine+balancing.jpg

Because the crankpin isn't drawn square to the countermass!

....Cotten

[pisten-bully]

...okay, I confess a bit of cornfusion here! IF a flywheel assembly is balanced as described, with the rods, pistons, and rings that are going into the motor...and the assembly (less one piston and rings) balances as described, then why bother figuring the balance factor? Balanced is balanced...right?

[pisten-bully]

This drawing really bugs me, Folks,..


Because the crankpin isn't drawn square to the countermass!

....Cotten

...doesn't appear the frame rails are level, either

[T. Cotten]

...doesn't appear the frame rails are level, either

Please visualize a line, Harry,...

Through the centers of the crankpin and main; It does not bisect the countermass.

....Cotten

[T. Cotten]

...okay, I confess a bit of cornfusion here! IF a flywheel assembly is balanced as described, with the rods, pistons, and rings that are going into the motor...and the assembly (less one piston and rings) balances as described, then why bother figuring the balance factor? Balanced is balanced...right?

In practical terms, Harry,...

Yes.

(Ironically, that's why we do not know the original factors!)

....Cotten

[pisten-bully]

Please visualize a line, Harry,...

Through the centers of the crankpin and main; It does not bisect the countermass.

....Cotten

I saw that Cotten! My pitiful attempt at levity was only to suggest the drawing (as copied) is not to be trusted either!

702B1A25-4FD6-456D-B41F-5E7ACA0E9CE1.jpeg

[pisten-bully]

In practical terms, Harry,...

Yes.

(Ironically, that's why we do not know the original factors!)

....Cotten

...then why all the discussion about balance factors? This is not directed at any one person Cotten, I'm simply trying to understand. What is a balance factor and why is it used, or not used? Seems to me that if you physically balance the flywheels as described, with both rods and one piston with rings then your motor will run smooth. But I read these treatises on flywheel balancing, math included, and don't see why?

[T. Cotten]

...then why all the discussion about balance factors? This is not directed at any one person Cotten, I'm simply trying to understand. What is a balance factor and why is it used, or not used? Seems to me that if you physically balance the flywheels as described, with both rods and one piston with rings then your motor will run smooth. But I read these treatises on flywheel balancing, math included, and don't see why?

Its worse than that, Harry,...

The true genius of the Founders of motorcycling has been lost with Time, and replaced with pontifications.

Its pseudoscience to split grams of mass when the motor doesn't even know it has two pistons.

....Cotten

[JTR249]

When I sent a piston to Ross Racing Pistons so they could make two Warrior .010 oversize for my 1950 Indian Road Warrior, Jim Mosher sent me an email and suggested I remind them that the originals were not made the same (sand-casting) as modern pistons (?). The reason is that modern, reproductions based on the old originals or period aftermarket pistons (which mine are--Robbins made for Warrior in 1950-1951) must have more clearance and somehow this affects the original balance factor.
Now, correct me if I misunderstand, if a rim is not true, it will slightly wobble if bad enough. Sometimes you can't detect it and this condition does not much affect your ride. Damage happens over time. If it is bad enough, you know it because you feel it. The internal parts of the motor are similar, I suppose. I don't mean to over-simplify here. Flywheels themselves have to be balanced as well as the reproduction pistons on the rods because of the difference in the very materials themselves. Jim Preussner said this to me recently about the Indian verticals. if this is not done correctly, the motor suffers damage depending on how much it is out of balance than the original specs.
What would be a worse case scenario if the balance were really off? Does it pull on the cam gears? Over-heat the motor?
Just trying to understand.
-JR

[T. Cotten]

Beware JR..

Balancing a motor is nothing like balancing a wheel, where mass is equalized. Motor balancing requires masses to be proportionately un-equal.

Motor balancing is not a science. It is only an applied technique to keep the motor from throwing itself apart. Different factors will give different performance characteristics, so it is also a 'tuning' tool. All motors have a 'balance', although not always ideal for its duty. Single-throw motors have forgiving advantages over motors such as vertical twins or Fours, in that there is only one reciprocating mass, and one rotating mass. The motor doesn't know if one piston is heavier than the other, and there is no place for it in the balancing equation.

Properly true'd, a 52% v-twin motor runs just as smooth as a 60% motor, but the low factor favors acceleration, whereas the high factor favors longevity and cruising. With a ~1500g reciprocating mass, eight points of factor is 120 grams!

Its not just about the flywheels. Replacing cast pistons with forged dramatically drops the factor, and vice versa. Its easier to lighten the pistons than to drill the wheels into Swiss cheese near the crankpin, and you often want to keep as much flymass as possible.

Motors are not balanced for the rider's comfort. The motor doesn't know there is a rider. When a top motormount comes loose, you feel it shake because the motor is no longer "balanced". Tighten the mount, and the shaking stops, because its back in "balance"!

As far as motor wear, it should be intuitive that when a machine is bouncing at idle, it is not balanced to turn that slow, and internal forces are maximized. Raise the idle to where it smooths out, and forces are then distributed, with less wear.

...Cotten

[JTR249]

Cotten,

That makes sense to me. Thank you for clarifying this.
I have often heard people say that if you get an antique motorcycle, you should probably be the kind of person that doesn't mind working on them a little.

Is the balance factor also why the 1946 Chiefs had idle adjustment on the grip? All factors designed to fall within a given range and not a single setting?

I know vertical Warriors all have something called an engine brace kit, which I have several of, though I never realized this was possibly the reason for them!
Do you think they just couldn't get the motor balanced properly because of the way they designed them?
Pete Sink said vertical Scouts were also bad about shaking too much.

Thank you for the lesson.
Much appreciated.
-JR

[T. Cotten]

Cotten,

That makes sense to me. Thank you for clarifying this.
I have often heard people say that if you get an antique motorcycle, you should probably be the kind of person that doesn't mind working on them a little.

Is the balance factor also why the 1946 Chiefs had idle adjustment on the grip? All factors designed to fall within a given range and not a single setting?

I know vertical Warriors all have something called an engine brace kit, which I have several of, though I never realized this was possibly the reason for them!
Do you think they just couldn't get the motor balanced properly because of the way they designed them?
Pete Sink said vertical Scouts were also bad about shaking too much.

Thank you for the lesson.
Much appreciated.
-JR

I know next to nothing about verticals, JR,...

But two crank throws makes for more opposing forces. V-twins are singles with two cylinders.

There is no perfect factor for any motor, only marginal ones. The whole magic of a single-throw motor is that it will perform over a wide range of RPMs with a wide range of factors, and its hard to mess it up. Verticals apparently make it more complicated. The brace must stiffen things, absorbing forces from some vector or another: http://virtualindian.org/Flywheeltheory3.htm

And know of no idle mechanisms other than on the carbs; I suspect you refer to the spark advance, which naturally affects the idle speed, and retarding makes it easier to get the 'crash box' in gear.

....Cotten

[tfburke3]

chief has throttle on bars,idle adjustment is on carb.
I often wondered if Indian even balanced every motor.This would very time consuming and maybe not needed if all components are the same.How far off can a run of flywheels be from each other?
Also how was original factor determined?Most likely trial and error,racing results etc.
Also I would not call using a recommendation from a scout motor builder with a land speed record picking a factor out of thin air.
Tom

[T. Cotten]

....Also I would not call using a recommendation from a scout motor builder with a land speed record picking a factor out of thin air....

He probably didn't, Tom!

He merely bowed to convention: the current pop harley factor.

In the early '80s it was 52; Something changed, and it wasn't the motors.

We can be pretty certain that Indian didn't use sixty.

....Cotten
PS: How many different factors did Mr. Mosher assemble and run?