Is a lightened flywheel overrated? (I think so)

[Milton]

"Thinking about #1, there is a 3 inch long bearing back there that most engineers would agree is way over-engineered for the task."

Now why would they do that? Why is it that every babbitt A that I have disassembled shows main wear the most at the rear?

#2: True, however, how fast must one shift? Not enough compression to slow the motor down before the car rolls to a stop? Est-ce que tu comprends speedshift?

#3: True again, but then the rotational momentum is diminished. I dislocated a friends neck once by spinning the tires in dirt and when the tires hit the pavement he was looking at the roof. Takes a lot to beat an A off the line, but after that it's all over.

#4: That's one that I never heard before.

#5: I'm with MikeK and the reduction of torsional vibration.

And most of all the light wheel allows my Stipe IB350 to announce itself very well at an idle.

[Pete]

Originally Posted by Craig Lewis

I utilized patterns from one of the Restorer series of books & cut these crank weights from 5/8 plate steel.
After grinding and dressing to fit the crank, the 4 together weighed 11 pounds just before welding them on.
The machinist who balanced everything commented what very little metal had to be ground from the 4 lugs to bring it into balance... so I'd guess 10-11 pounds is about the average.
It seems I had 30 lbs cut from the flywheel (haven't got my notes handy)
I still haven't run it, but now you guys got me worried cuz I hope it doesn't lose that distinctive low Model A idle with the light flywheel!

I hate to be a wet blanket but the guy that did your welding should go back to welding school.

[Craig Lewis]

Originally Posted by Pete

I hate to be a wet blanket but the guy that did your welding should go back to welding school.

Oh really? It was tig welded at a reputable welding shop because I didn't have the equipment at that time. I migged the weights in place, then it was all preheated in an oven, tigged while hot & placed back into the oven to cool overnight.
You're entitled to your opinion Pete, although several people have commented to the contrary.

[RockHillWill]

My opinion is that is a VERY nice approach.

The more I learn about MIG welding and the effect that the rapid cooling has on the neighboring material the less I like it.

The alignment clamps are a nice touch. I know some that do not use them.

Nice work!

[Special Coupe Frank]

I think Herm made a good point ( as usual ), about the center main and crank flex.

If counter-weights are added to the stock crank or a weighted crank is used, the flywheel should probably be lightened accordingly to keep the entire assembly at stock weight.

And to borrow a statement from Steam heating guru Dan Hollohan, "the dead men knew what they were doing" in terms of design and engineering.

And there was at least one autombolie that employed a flywheel at both ends of the crank: the Rickenbacker.

SC Frank

[Jim/GA]

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Originally Posted by Craig Lewis

It seems I had 30 lbs cut from the flywheel (haven't got my notes handy). I still haven't run it, but now you guys got me worried cuz I hope it doesn't lose that distinctive low Model A idle with the light flywheel!

It might.

Put the engine together with these weights and the lightened flywheel and run it on a test stand. See how you like it. Before getting it all buttoned up, if you don't like it, you can get a different flywheel and try again.

A new tight engine isn't going to idle as nicely as it will after it wears in and loosens up, so run it on the stand for a while, then decide how you like the idle.

[BRENT in 10-uh-C]

Originally Posted by Special Coupe Frank

I think Herm made a good point ( as usual ), about the center main and crank flex.

If counter-weights are added to the stock crank or a weighted crank is used, the flywheel should probably be lightened accordingly to keep the entire assembly at stock weight.

And to borrow a statement from Steam heating guru Dan Hollohan, "the dead men knew what they were doing" in terms of design and engineering.

And there was at least one autombolie that employed a flywheel at both ends of the crank: the Rickenbacker.

SC Frank

Why?? Again, this is counter to what I suggested.

Also, just how much does the crankshaft bend with a 40 lb flywheel vs. a 62 lb flywheel? I have not measured it so it is only speculative however by my thoughts, it is very marginal as compared to the flex the crankshaft will see with a higher compression head and its increased cylinder explosions.

[Pete]

Originally Posted by Craig Lewis

Oh really? It was tig welded at a reputable welding shop because I didn't have the equipment at that time. I migged the weights in place, then it was all preheated in an oven, tigged while hot & placed back into the oven to cool overnight.
You're entitled to your opinion Pete, although several people have commented to the contrary.

Your method was good and you will most likely never have any problems with them, BUT, the welding itself looks like an amateur did it.
I was a welding inspector in the aircraft industry at one time and I know what good welding looks like. Besides inconsistancies, you have undercut.
Another thing that is bad is mixing 2 different kinds of welding. Mig and tig, even if it is just tack welds. Mig wire is far different from tig filler rod in most cases. When you have to tig weld over mig tacks it can cause a hard spot that may become a stress riser.
By the way, there was a thread on tig welding on the HAMB awhile back and you can go there and see what good welding looks like.

[MikeK]

OK, time to throw a wrench in the works-

Brent's initial post asked "#5: (Add your reason here...)"

This fits #5: Reaction couple.

All rotating assemblies are gyroscopes. The crank and flywheel are BIG ones.
Any movement of the vehicle like turning or going up and down on the suspension will induce a counter torque along the axis of the flywheel. That means a bending force between the the flywheel and crank. Where? At the rear flange! What "takes" (holds up) that load? The rear bearing.* A hard bounce or turn at 3000 rpm may give you a torque equivalent to a 1000 lb dead weight on the end of the crank. That force may be up, down, left, right. Bye Bye rear bearing. Cyclic stress on the flange. Less flywheel weight = less force, so . . .



OK, what about reaction couple from the heavy spinning counterweighted (or -un) crank???
Since the crank has a bearing at each end, the force is applied to the block ends, not the external flywheel flange.

NOTES:
* Load at the center main bearing will be much, much less, as a lever arm is involved. Distance from center to rear main contact center is one long arm of a torque lever. The other lever has a much shorter length, the CG of the fly to the rear bearing contact point. Crank deflection (a Young's modulus function) will determine how much off-axis twisting the journals do within the bearings.

My personal analysis of all this- You can run the engine wide open on a dyno for 80 years with any weight flywheel or crank. Near zero stress on the rear flange and rear bearing. If you DRIVE the vehicle, wear and cyclic fatigue damage accumulate in those two places. Drive like grandma, little to worry about. Drive like Pete, you had better cut down the rotational elements or else!

[Pete]

I love it.

[Chris in CT]

OK,OK I was going to try to stay out of this, but I just can't help myself! I'd like you to think about the word, "damping" and throw the balance weight out the window for a moment. That 63 # flywheel was put there to "damp" the impulses from the cylinders as they fired. The 63# flywheel also allowed the driver to "set it and forget it" as far as the timing advance lever was concerned, since at the lower compression of the stock engine the revolving flywheel would easily overcome timing inconsistencies.
What happens with the so-called "counterbalanced" crankshaft is that each of the slings (counterweights) "damps" the combustion impulses right under the subject cylinders, rather than at the end of a long, twisty, spindly piece of forged steel. Once you have effected that "equalization" of combustion impulses, it is no longer necessary to have 63# of cast iron at one end of the engine - in fact, it is counter-productive because it will continue to cause the crankshaft to twist with each impulse where with a lightened flywheel that twist will be proportionately reduced.

The only way to actually prove this to our scientifically-minded brethren is to perform a Fourier Analysis on the rotating assembly, a complicated process requiring a lot of time and equipment.

Oh, incidently, have those of you who have removed 20# or so from your flywheel noticed that the engine is much more sensitive to the position of the ignition advance lever than it was when the flywheel was full weight? I have. So much so that I am tempted to go out and get a centrufigal dizzy! When I go for a drive, it keeps me quite busy trimming the thing. Happy Motoring, Guys!
Chris

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www.burlingtoncrankshaft.com

[Tom Wesenberg]

Whoa! Now my head is spinning!

Good thing it's hollow so there's less rotational mass, otherwise it would fall off!

[BRENT in 10-uh-C]

Originally Posted by Chris in CT

OK,OK I was going to try to stay out of this, but I just can't help myself! I'd like you to think about the word, "damping" and throw the balance weight out the window for a moment. That 63 # flywheel was put there to "damp" the impulses from the cylinders as they fired. The 63# flywheel also allowed the driver to "set it and forget it" as far as the timing advance lever was concerned, since at the lower compression of the stock engine the revolving flywheel would easily overcome timing inconsistencies.
What happens with the so-called "counterbalanced" crankshaft is that each of the slings (counterweights) "damps" the combustion impulses right under the subject cylinders, rather than at the end of a long, twisty, spindly piece of forged steel. Once you have effected that "equalization" of combustion impulses, it is no longer necessary to have 63# of cast iron at one end of the engine - in fact, it is counter-productive because it will continue to cause the crankshaft to twist with each impulse where with a lightened flywheel that twist will be proportionately reduced.

The only way to actually prove this to our scientifically-minded brethren is to perform a Fourier Analysis on the rotating assembly, a complicated process requiring a lot of time and equipment.

Oh, incidently, have those of you who have removed 20# or so from your flywheel noticed that the engine is much more sensitive to the position of the ignition advance lever than it was when the flywheel was full weight? I have. So much so that I am tempted to go out and get a centrufigal dizzy! When I go for a drive, it keeps me quite busy trimming the thing. Happy Motoring, Guys!
Chris

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www.burlingtoncrankshaft.com

Yeah, me too Pete!

Hey Christopher, I'm glad you jumped in!! Thanx!! So using a Burlington crank as the baseline, what do you feel is the optimum weight for the flywheel/PP assembly on your crank using a 5.5/5.9 head and a Stipe cam that makes good torque in the low range??

[Allanw]

Originally Posted by Tom Wesenberg

Whoa! Now my head is spinning!

Good thing it's hollow so there's less rotational mass, otherwise it would fall off!

Haha!

[Vic in E-TN]

Very interesting reading from Mike K especially. I have a couple of counterweighted cranks and lightened flywheels and I like the performance. I have mostly high compression heads. There are too many variables to make a definitive assessment.

Think about this for a minute. If you want your engine to last as long as possible you should put the best shocks on your car. They will reduce body movement and reduce the resulting stresses on the crank/bearings.

Vic

[MikeK]

He He, now I'm loving it too. I used to make engineering students pee their pants by chalking "Fourier" on the board. Applied to physical materials harmonic analysis problems, you'll need to decide what transforms are applicable. I vote for using eigenfunctions as delineators. LINK

Sometimes in engineering you hit the theoretical wall, and just need to do hard physical operational testing if you want answers. In lieu of setting it all up on a test stand (or cleaning up all the puke after the above lecture) I offer the following alternative calculator. I believe this will give the answers Brent seeks.

[BRENT in 10-uh-C]

An OUIJA board!! Come one, ...come all as we gather around the table...

[dumb person]

If i was not dumb i would be able to do those calculations...

[BILL WILLIAMSON]

Originally Posted by Tom Wesenberg

Whoa! Now my head is spinning!

Good thing it's hollow so there's less rotational mass, otherwise it would fall off!

Tom,
Don't forget the sinus, (sniff!) cavities, without these green caves, we could only see our lint filled belly buttons, I pluralized it in case you have 2, on the positive side, you would NEVER stain your buckskin loafers, or burn out your eyeballs watchin' that "one of a kind" sunset at the beach, provided you live on the LEFT coast! You folks on the RIGHT coast don't know what you been missin'! Bill W.

[Pete]

"I vote for using eigenfunctions as delineators." LINK

Ya know, now that you mention that stuff, I actually remember about 20% of it....lol