'27 JD Cut Down Project - SWAN

[aumick10]

I read a 2005 post on this issue that had a very good explanation of the effects of balancing.
Most of my experience is with street Evo's and drag bikes.
The drag bikes were built to a very specific set up to run over 200 hp at 7500-8500 rpm.
Those balance factors were used for mechanical reliability, rider comfort did not come into it, especially for electrical items.
Street bikes are not a sensitive to different balance factors, so these have a wider plateau as you mention.

Cheers,
Mick

[T. Cotten]

What was the factor, Mick?

...For twice the rpm of a street machine?

Thanks in advance as always,

....Cotten

[aumick10]

Tom,
It was over 20 years ago, but from memory it was over 60%. This was only part of the overall design specs.
Light wheels but heavy rods and pistons.
We would usually have to add weight to the wheels, typically lead or Mallory metal.
Mick

[T. Cotten]

I remember sixty became the "sweet spot" back then, Mick!

But in the early '80's the speed shops (like Lakeshore) used 52%, and they ran smooth, too.
(And it seemed like mine jumped quicker.)

That was for Pans that back-calculated to ~57% OEM.
But 'modern' machines had different frames than Steve's, too.

....Cotten

[aumick10]

It just goes to show how subjective the balance factor is.
Bike weight, gearing, riders style all come into account when deciding where to balance for.
Mick

[T. Cotten]

It just goes to show how subjective the balance factor is.
Bike weight, gearing, riders style all come into account when deciding where to balance for.
Mick

Y'know, Mick,..

I never found a V twin that was really out of balance.

(Seen a few riders though.)

....Cotten

[aumick10]

The factory balances motors when they manufacture them, but only to a cost and range of tolerances.
If a V twin feels really out of balance, you had better check your crank pin real quick in my experience.
It also depends on how much padding the rider is carrying.
Mick

[T. Cotten]

Yes I agree, Mick!

Most 'bad vibes' are mechanical issues.
But if the Factory missed the 'ideal' of sixty by three points, consistantly, that's a lot of rod top.

At risk of repeating myself, re-balancing an overhaul of a 'stock' HD is only an exercise in feeling good.
But grossly different rods or pistons demands it to sleep good.

Even if it would have run fine anyway;
My concern for Steve's project is the much different frame, which might like a different factor better than the modern ideal.

...Cotten
PS: As some of us have experienced, just losing a top motor mount bolt is enough to 'put the motor out of balance'.
(A lot of lot of padding "payload" aught to dampen vibes!)

[ryan]

I was just reading about static balancing a Harley motor. I do not know enough about it to know if the process is correct though.

http://www.caimag.com/wordpress/2011...;-how-i-do-it/

[T. Cotten]

I was just reading about static balancing a Harley motor. I do not know enough about it to know if the process is correct though.

Ryan!

Before I spread my cookies where I don't want them,
This isn't the guy who shaves his female tops to supposedly match the males, is it?

....Cotten

[ryan]

Cotten,
It sure is the same guy. He sure tore the one rod up.

From the article:
"Why I decide to take the weigth of the connecting rod end instead of the piston,if customer want to change piston in the future to similar he will not change the end result by much and also connecting rods are there for a longer period of time ,first thing to do when doing job like that is planning where you want to take off the material without weakening the rod itself."

[Rubone]

If you have females needing to shave their tops you've got a bigger issue than balance!!

[T. Cotten]

Gosh Ryan,

We can now call over-thinking-to-the-point-of-destruction a syndrome;
I fear he got this bad idea from S&S techs.

The rod tops, the masses that actually move in different directions, were virtually the same to begin with.
(Who can tell which is which in my attachment?)
Half a female rod should always weigh more than the same proportion of the male because its a heavier rod.

But the bottom halves move virtually in unison, as one mass.
Mutilating the female is pointless and futile.

...Cotten
PS: And I'm absolutely certain Wiff knows better, Steve!

[Steve Swan]

Thank you Gentlemen, each and everyone for your replies. I have been down since Friday, March 15 with the worst cold I have ever had in my 67 years. Haven’t been sick in over 4 years, but this one kept me house bound until yesterday when I ventured up into my shop to help my buddy get the tanks fitted on to his ’29. Anyway.

Again, thank you again for sharing your experience. Re-reading your comments, the one thing I need to redo is get the rods as level as my eye can tell and then re-weigh the rods while paying attention to Mick's "fudge factor." And since I am in the Northern hemisphere, no worries about weighing the rods upside down….

Cotton, you mention “with a brand new modern rod, one must jump through the hoops.” In terms of my application, can you explain a bit more? (Also, I am going with a stock, unaltered JD frame, thanks to Mick!)

I am planning on following the procedure discussed in Uncle Frank’s Questions & Answers; i.e., assemble the flywheel assembly complete, minus one piston, pin, spiral keepers and rings. With the assembly sitting on perfectly level knife-edges, the flywheel should stop at any point in the 360 degrees of rotation.

For what it is worth, I called Truett & Osborn and happened to have the good fortune to speak with Paul Osborn; they set up my lower end on my restored ’27 and I would say it is amazingly smooth at all speeds, no hop down low and above 50 mph, things start getting buzzy. When I asked what balance factor they set their flywheel balance to, Paul said 60%. Out of sheer ignorance on my part, is a 60% balance factor any different than balancing the flywheels so they stop anywhere in their 360 degree rotation? If you can explain this in country school 8th grade terms, I would be best for this brain as I have no where the experience or expertise you gentlemen possess.

On the one hand, I want a smooth as possible motor within as wide and rpm range as possible, and on the other hand I realize we are talking about a ’27 JD which isn’t exactly rocket science, but it does have new flywheels, rods and pistons so I don’t want to, as Cotten says, “over-think to the point of destruction.”

Looking forward to hearing your thoughts!

[aumick10]

Steve,
I can't remember if you mentioned which flywheels you are using. OEM or Truet & Osborne. This will change the way you balance this motor.
Regardless of the wheels, the procedure for measuring the weights is the same. As you mentioned, the rods need to be horizontal when you weight each end. I think cotton posted a picture of a good tool to ensure this.
You will find that the Carrillo rods you be will much heavier than OEM rods, maybe twice the weight. Using OEM wheels will mean more work to balance them by adding or removing more weight. T&O wheels are probably heavier to start with ?
Because the Carrillo rods are heavier to start with, any discrepancies in top and bottom weight will be a bigger percentage of overall weight, if you don't get it right.

As mentioned in numerous other posts, the balance factor is very subjective. As a general rule, a lower balance factor will move the vibrations in the vertical plane, the higher balance factor will move the vibrations in the horizontal plane. This comes down to personal preference. I am surprised T&O used 60% as a balance factor for such a low revving motor. As you say, it is a bit "buzzy" over 50 mph, I would expect that on a lower balance factor motor. How is it at 100 mph?

Now to the actual balancing.
Once you have done all your measurements, and decided on what your balance factor will be, there are two ways to balance your motor.
In dynamic balancing, the total calculated bob weight, including the crank pin, is clamped to the crank pin and rotated. This is done on a dedicated machine, like a tire balance. This is typical of what the factories use. Can also be done on knife edges with a manual interpenetration of where the heavy spots are.
Doing this on a machine will tell you where to add or remove weight on the screen, probably even do this automatically, as you can see in a lot of OEM wheels.

The most common way for people to balance flywheels is the static method. This is as you described above. Setting up the flywheels with counter weights to visually identify when a flywheel will settle, regardless over where it is first placed on the knife edges. Adding or removing weight is an integral part of this process.
I don't have a copy of Uncle franks book, but it seems to me that was the best practices at the time, before we knew what factors influenced the engines feel. You may be lucky and have the parts add up to the correct bob weight.

I was taught to balance motors using the S&S system where you balance each individual flywheel.
I have found over the years that not all OEM wheels have the same density from the factory. Occasionally while drilling a hole in the wheel to add weight, I have come across an air pocket in the casting.
If the flywheel is balanced as a unit, this density difference can manifest itself as a side to side motion. This is unlikely to be, as it is probably such a small force, or felt, but it is why I prefer to balance each wheel individually. If each wheel is individually balanced, this effect it probably negligible. Once again, this is the way I know to do this.

Cheers,
Mick