At home flywheel balance....

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nm9stheham said:
The source of error will be the bearing stiction that has been referred to and is a very real issue. (And which is something I have actually done and have seen the criticality of having essentially 0 bearing stiction.)
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Great, so what will my margin of error be from stiction? Do you think it will create more of a margin of error than what the factory or aftermarket allows for with flywheels?
 
Well, to figure that out, on would have to figure up the range of weight moments, and compare that to the moment required to overcome stiction in this setup. I am not totally clear on the process to be used for balancing this, but would you remove some metal on the wheel and see if it balanced against a known weight on the opposite side?

I looked quickly to see if I could find some stiction numbers for a similar bearing but was not successful. Besides, it will vary with the side load on the bearing. Probably the best way for you is to test it directly on your setup. With the flywheel unmodified (neutral balanced), I would gently hang some very small weight from a light string at the outer periphery (so it is hanging straight down at + or - 90 degree point on the wheel) and see if it moved the wheel. Then keep increasing the weight 'til it could move the wheel. The hang it from the other side and repeat. You my then even want to move the wheel 90 degrees and repeat the measurements again. I would use a powder loading scale since they are made to go down to very small fractions of grams with accuracy. (And weigh the string too!)

Take the average of those weights and the distance from the center to the periphery and multiply and that will be your average stiction moment and that will be your margin of error.

BTW, on thing you are fighting here is the heavy weight of the wheel, which makes the stiction even higher, since stiction/friction generally increases in proportional to weight loading.
 
To be honest, I've already checked the bearing friction, to over come it, or to show movement on the flywheel from the neutral balanced position is 2grams at a radius of 7.750 inches. To give that some perspective to those who don't know what 2 grams is, it's the weight of a 1 cent coin.. Also the bearing has been positioned at the center balance point of the flywheel, which eliminated any side loading. I've got pics of how this was also done. I want to get a few other things sorted out with this before I have to write a long post on this subject.
 
OK, so that works out to +/-3.44 grams at 4.5 inches. Or about a +/-3% error from the desired weight, and works out to +/-39gr-cm of moment. I have no idea how much that would effect overall external balance but that seems to be getting fairly well out-of-bounds for higher RPM crank balancing but within bounds for a low RPM grocery-getter. (That's simply based on what I can find online. I always just pay to have my stuff balanced, since I don't have any equipment.)

Another question has been referred to: How accurately can the plasticene's weight be centered at the desired (opposite) angle and 4.5" distance? Perhaps there could be a magnetized weight used instead. But any redial error adds on.

And for the stiction....you might be able to derive a more accurate number by varying the plasticene weight above and below the target value to see where the wheel rotates in opposite directions. Might work if the balls are consistently smooth in both directions, and you can find an easy way to vary the weight. Perhaps a water vial attached to the weight with a burrette..... yeah, I know, just thinkin' out loud.

BTW, are you using any special lube on the bearings? Not sure if anything would help or hurt.
 
The large lump of plasticine was just for the picture I took, small amounts of it help when determining weight adding and direction. That error rate is within what you will find with factory flywheels , or converted ones that use the Mopar drilling diagram. Most balancing vibrations shows up at low RPM's . Experimenting with no lube, and light lubricants.
I'll talk more about this stuff when I get a little more time to write an essay on it and post some pics.
 
Just to update, I made an error in how many grams it takes to move the flywheel and overcome any friction in the bearing. it's actually 1 gram at 7.750 inch's , not 2..
I have now had 2 different stock 360 flywheel on the fixture and both of them have the center counter balance hole a few degrees off vertical. One slightly more off vertical than the other. Technically they should both be smack bang in the vertical position..
That's quite interesting in relation to modifying your flywheel using the Mopar instructions..
 
Ok, time to thrash the naysayers... :)
Here is the tool I made to find the center of gravity the flywheel. This is done to remove any side loading on the open case ball bearing.
View attachment Flywheel_002.jpg

The tool is then set in a vice and leveled vertical.
View attachment Flywheel_003.jpg

The flywheel is set and the center is recorded.
View attachment Flywheel_004.jpg

The bearing is then machined into the adapter so it's center of gravity lines up with the flywheel. This is the clutch side of the flywheel.
View attachment Flywheel_005.jpg

Crank side of flywheel.
View attachment Flywheel_006.jpg

I then made a jig using an old trans flexplate with an arm on it. I'm able to move the arm in an arc and add weights to the end of it to find the weight needed to make the 360 flywheel neural balance again.
Once this is was done, I then transferred the jig to another flywheel that was neutral balanced.
I then fabricated a weight to work against the jig. This then converts the flywheel to external balance , much the same way as McLeod etc does.
The weight is then clamped to the wheel, drilled and tapped for the correct strength bolts.
The internal lip of the flywheel prevents it from flinging off due to gyroscopic forces.
View attachment Flywheel_007.jpg

Bench view.
View attachment Flywheel_008.jpg

View attachment Flywheel_009.jpg

View attachment Flywheel_010.jpg
 
OK, a few interesting things. First of all, the Mopar external balance modification guide that is posted up now and again is not the "be all to end all" .After checking out a few unmodified stock flywheels I've come to the conclusion that the factory flywheel balance job and posted modification guide is not as accurate or critical as some people think. It's pretty much just to get you in the ball park.
I've got a suspicion that the 3 large holes were drilled at one phase of the flywheel production and then some smaller holes were drilled later at the balancing phase. Lot's of people have drilled those 3 large holes in the past and not experienced any balance vibration problems, so that also shows that the factory balance is not so critical. After all, how many people convert to a manual gearbox using second hand factory parts and bother stripping the engine to balance the flywheel with the crank, even if it's been balanced to another engine some time in it's past which you don't know about?
Also, why did Mopar drill those friggin big holes to external balance the wheel? Well, they did it because it was cheap, cheaper than casting a new wheel with a counter balance in it like this.
This is a Ford 351 Cleveland wheel.

View attachment Clevo_003.jpg

View attachment Clevo_002.jpg

Ford 351 steel flywheel with counter balance holes drilled into it.

View attachment Clevo_001.jpg

They also did not expect anyone to use an external balance small block crank in a performance application, so any issue with the holes weakening the flywheel was a mute point.
 
Update ...Had the balance electronically checked yesterday, was within what the machinist considered acceptable.
 
I must apologize, I thought you were jumping through all these hoops to be able to balance a flywheel to any spec you desire, not just to copy one balance to another flywheel. Why not just bolt them together 180 degrees out and add weight to the one you're wanting to change, until the pair is neutral? That's what the flywheel shops do.

FWIW, Chrysler drills the small holes first. All flywheels (at Chrysler anyway) start out neutral and that's how they balance them. If it's for an externally balanced motor, then they grab a N balanced wheel and drill drill drill.

In discussing the aluminum wheel for EFI Magnum 5.9 applications, my flywheel manufacturer said that he thinks the factory balance has an error of +/-10%. What would you guess that the error in balance between the two wheels was in your findings? Did you weigh the two external balance wheels to see how much difference in overall weight there was between them?

What did your machinist give you for spec and tolerance for "acceptable"?
 
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