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Background: A few years ago, I balanced my new Shovel stroker flywheels (static) and used 100% of rod & crankpin "rotating wt" with 60% of reciprocating weight, and I had discussed that 60% factor by phone with S&S......Now I'm considering putting stroker wheels (HD 45 stroke) in my
Indian 741 Scout (makes 50 ci), and one of the net sites I visit has had a discussion of balancing factors for Indians, with one response of 85% balance factor!!

There are also lots of obsolete "prescriptive" methods printed in old literature too ("add 2.5 oz to reciprocating wt")....also, some use a different balance factor for higher reving Scouts vs lower reving Chiefs.
So, other than 42 degree vs 45 degree engines, are there any differences in HD vs Indian which cause different balance factors to be different, and what does S&S recommend??

On Friday, Dyno Dan responded:
We always recommend 60%. I have seen them anywhere from 52-62% and it seems to be a matter of personal preference of where you want it to run the smoothest.
S&S Tech
Dyno Dan
Voice Phone 608-627-1497
Tech Fax 608-627-0324
Installation and set up manuals can now be found at sscycle.com

On Friday,  24 Sep 1999 06:54:42 -0500 Guy wrote:
Thanks, Dan....but I have questions: what is the relationship between where it runs the smoothest and balance factor?  ie, for discussion, do you use 52% if you're typically running 4500 or more RPM, vs 62% if you're typically cruising at 2200 RPM?  Is there any difference in vibration characteristics because of different cylinder angles of 45 or 42 degrees?  If you have messy technical stuff on these questions, please don't spare me, I'm an engineer. My intent is to disseminate this info to Indian websites....Thanks again.  -Guy-

Dyno Dan @ S&S Technical Services responded on Fri, 24 Sept. 1999 11:28:58 -0500:
I'm sorry we do not have anything in print, but the numbers we use were determined years age by actually building an engine and riding it, then changing the factor and riding again and deciding what worked the best - so I am afraid I have no documentation.
 
 
From: Cotten <liberty@npoint.net>
Guy! Bless S&S! I have relyed on them religiously for my Milwaukee projects for nearly 25 years. However, Lets rememember that there will be differences of perspective when we apply their commercial performance formulae to our calamitous antiquities. Even within the H-D spectrum they only supply super-light off-the-line go-faster wheels, whereas our side-valves really do appreciate a little flywheel torque and dampening effect. (Bless T&O for the alternative)
Your questions to S&S and their replies both talk in terms of vibrations. It becomes important here to distinquish the difference between rider-felt sensations and the harmonic push and pulls of flywheel thrust that balancing actually affects. Distracting vibrations are primarily a result of power train and chassis variables, as Moen has outlined <resonanc>, or at worst, out of true flywheel assembly. A properly fit and true crank will perform smoothly over a great range of factors, but will accelerate and develop power differently. This is the grace of a V-twin. Picking a factor is a means of tuning a motor for a particular duty: Low to drag race, or optimized higher to reduce those harmonics and prolong the life of the motor, as well as to allow it to comfortably cruise at the widest possible range of rpm. (Low factors seem to always want to be in constant acceleration, almost like dropping your countersprocket down two teeth.)
It does not surprise me that S&S does not have hard numbers to justify the 60% factor (for H-D's). This number was carved in granite by the pioneers long before strobelights, tachs, and dashpots became the state of the art.
I bow to the experience of other Listers who assert that 62 to 65% is
optimum for Chiefs. (Scouts? 101's, Any feedback?)
 
 
From: Duff <MICHIGANDER@Worldnet.att.net>
The 64% is about what you get with the rods plus piston complete with pin and keepers.

 
From: indianjohn <johnmarg@pilot.infi.net>
While cleaning my garage of sundry clutter, I came across some notes Imade while rebuilding a '41 Sport Scout and also my '38 Chief. Among them were the weight measurements I made for balancing. Using the values for the Chief and back-calculating the factor to agree with the Indian method of subtracting one complete piston assembly from the reciprocating weight, I arrived at about 63.5% or very close to the 64% stated in some messages. However, when this was repeated on the Scout, the factor arrived at was about 71%. I believe that most of the dissertation about factors has addressed the Chief so I am submitting this only to point out that a difference exists. The values represent actual measurements and I do not know how the aftermarket piston weights compare to factory original. Incidentally, the Scout rods were the heavier of the two.

Both engines were completed prior to this workshop and I used a 60% factor after having a conversation with the S&S tech dept. I was told that was the factor that they had arrived at for any V-twin engine and the result of their own experiences. The owner of the Scout now has 1000+ miles on the engine and says it is the smoothest it has ever run in the 20+ years he has had it, altho I don't know what, if any, factor the previous builder used. The Chief is awaiting paint to be completed before a trial run is accomplished but I am afraid gasoline may become obsolete first.

As for the 2.8oz additional weight cited in the old Q&A, I came across another "Service Shots" that noted that pistons made prior to 1941 were 4 oz heavier than current ones. Substituting these values in my Chief measurements resulted in a factor of 61% without the added weight and 66% after the 2.8oz correction. possibly, this instruction addressed these earlier parts.

Regarding methods I have seen that cited the piston to be assembled to a specific rod, I summed the total weight with the piston assembled to the front rod and again with it assembled to the rear and, not suprisingly, came up with the same total weight. As gravity should force the center of the weight mass to a point directly below the crankpin, I fail to understand what difference it should make in the end result. In fact, the Indian instruction I have from 1940 states the one piston to either front or rear rod.

I don't know what, if any, value this has but is my observations are based on actual measurements.
 
 
From: Guy <guyiii@home.com>
Excellent post, John....I want to make sure I understand, tho: didn't the Scout builder use about 71%?
 
 
From: indianjohn <johnmarg@pilot.infi.net>
guyiii, Unfortunately, we did not check the assembly for factors prior to tear-down. I used 60% when the engine was reassembled. My 71% cited in the message was based on the measurements I made at the time and reflects what the factor would have been had I used the procedure outlined by the Indian 'Service Shots" about balancing. I arrived at it as follows: each piston assembly weighed 336 grams with the small ends of the two rods totaling 464 grams for a total reciprocating weight of 1136. From this, I subtracted one piston assembly for a total factored weight of 800 grams. Dividing this by the total reciprocating weight of 1136 I arrived at 70.4% factor. For convenience, I left out the fractional grams in this description, the actual value is closer to 71%. (Did I calculate correctly?) In other words, the original factory factor was about 71% provided aftermarket and original piston weights are comparable. The previous builder was mentioned to point out that the statement about the "smoothest ride" was in comparison to an unknown value.
 

From: Matthias Elvenkemper <elvenkemper@unidui.uni-duisburg.de>
Late Indian Sport Scouts had a balance factor of 82 %. This figure was derived from an untouched NOS Sport Scout motor. Before disassembly of the wheels we checked it with the usual Indian "knife edge" method with one piston incl. rings installed on male (rear) rod and the flywheels were exactly balanced like described in the manuals. Three different methods (including a very complicated one that involved higher mathematics and kinetics) and were then used to find out the original factory balance factor, the result was always 82%.

A friend will lend me a pair of Chief flywheels, rods and an original piston. Will have balance factor checked with the same procedures.
 
 
From: indianjohn <johnmarg@pilot.infi.net>
If the factor is calculated using total weight instead of reciprocating, then the result would be in the 82% neighborhood. This is one of the methods described in the Q&A. ie. the balance weight is the total rotating and reciprocating weight less the weight of one piston assembly.