Flywheel Balance Factor for VL Motor

[DanM]

I have only balanced 1 set of flywheels so have no experience with how it affects the feel of the bike. What would we feel if we took the same engine and it was at 50% and we moved it to 60%? Or 40%? I rebuilt my 26 JD and had almost no ride time on the bike. When I took the engine apart it already had some kind of I believe UL piston in it. I used some new aluminum "high compression" pistons from a distributor in the hobby. We balanced each wheel using 58%. We needed to add lead to the holes that were already drilled, and even drilled more to I believe (7) deep, 1/2" dia holes in each wheel, pounded in lead, then threaded in a bolt to secure it, and cut it off flush with the wheel.

In a search of posts I found one person who did back engineer his 45 wheels and found a set at 44%, and most at around 50%.

For my bike, if I rev the engine on the rear stand it will "dance" on a smooth floor. Not at dead idle, you need to rev it noticeably (not a normal practice). The 64 panhead does not do anything like this. Riding, there is a pronounced vibe at low speed, which will make the front fork "bounce", (some improvement by retarding the timing) say in first as you move from a stop, or at a walking speed, but in riding speed, say 20 and up I don't feel any noticeable vibration. I've had it to 65 mph. So, any vibration I am thinking to be worried about is down low.

It is my understanding the balance factor can affect the range the vibration will occur- meaning one factor could move it to an upper rpm range, and another to a lower range? I suspect its better to have a vibe at a low speed low rpm, rather than upper range where riding occurs mostly?

Thanks to everyone for this discussion.

[fillibuster]

Dan, thx for your discussion.

24 years ago I brought my Chief engine to an exceptional builder, and we did the engine together. He had a small handbook on balancing, wish I had a copy.
I elected to NOT change any balance factors, but wanted to analyze and find out what my present factor was. All the weighing on the balance beam and hanging from a string and bob weights and static balance of each individual wheel, all these practices were exercised. My factor was 62%. I loved it, and I might have loved it at 60 or 55 also as this was my first Chief, my first Indian. I did a lot of heavy work with side car, and a lot of 70 mph (74", btw). I thought it was at its smoothest at 65-70 mph, and I often ran the 27 tooth sprocket solo, 23 with sidecar.
I rebuilt the engine with T/O wheels that were balanced at 60%. I still love the bike, but somehow it's not the same, (or I'm not the same). I think the sweet spot is slower. I know the books (and experts on commentary) have said it would be so, but from experience I have to say that I tend to agree.
breakfast is served, goodbye

[Buster]

Please excuse my stupidity, but I have one more question. I want to understand how to back calculate the original balance factor on an unmolested set of flywheels (not that I have any). I have the reciprocal weight, the rotating weight, and can calcuate what the bobweight weight would be to balance the full flywheel, rod, piston assembly. What is the specific formula for back calculating the original percentage of balance. I know this is simple, but I am very mathmatically challenged.

[T. Cotten]

Buster!

Let's keep it simple...

You don't need to even know the rotating weight.
(That's often only a check on the accuracy of the rest of the weighing procedure.)

To "know" the reciprocating mass or weight, you must not only weigh the piston assemblies complete, but you must know the weight of the rod tops.
This means the top "half" of their mass.
So just like if you put the front wheel of a level bike on one scale, and a scale under the rear as well, adding the two scale weights will give you the total of the bike. In reality, some of the front presses upon the rear scale, and some of the rear upon the front. You can't cut the bike in half, but you still know which half weighs what.

"Hanging" rods level to weigh each end achieves this. My previous photo shows a direct method using the crank to "hang" them.
Thus adding the two rod tops to the two piston assemblies gives you the reciprocating weight.
When you place the assembled wheels on edges, and add weight to the the rods until the assembly balances, then the added weight plus the rod tops is your trial "bob" weight.
Dividing the the "bob" by the total reciprocating weight results in a percentage, and that is your existing factor.

....Cotten
PS: If the wheels have been split, a truly exact measurement of the original factor has been lost. Even on a dynamic balancer with bobs conjured to simulate the assembly, each "truing" of the wheels will produce a slightly different result.
PPS: The wide edit window of this site is greatly appreciated! Shoveling slush to keep water out of the basement has me distracted...

[cdndewey]

Please excuse my stupidity, but I have one more question. I want to understand how to back calculate the original balance factor on an unmolested set of flywheels (not that I have any). I have the reciprocal weight, the rotating weight, and can calcuate what the bobweight weight would be to balance the full flywheel, rod, piston assembly. What is the specific formula for back calculating the original percentage of balance. I know this is simple, but I am very mathmatically challenged.

Try this link....

http://www.shovelhead.us/forum/showthread.php?t=80666

[T. Cotten]

I wish I could view the link, Dewey!

But they barred me without notice.
(Apparently I didn't fit their lifestyler profile.)

For those who want to read a basic V-twin motor balancing discussion without jumping through hoops, try http://virtualindian.org/1techflywheel.htm.

....Cotten