Is a lightened flywheel overrated? (I think so)

One of the better discussions on the forum that I have read in quite a while. Lots of reasoned opinions and no name calling.

Well done and thank you.
 
Brent, excellent topic... Here's my quick 2cents worth. I've driven and used both in my persnal engines and quite frankly I can't tell much difference, except that a stock flywheel definately enables the car to idle much more smoothly than one that is lightened. I think that was the intent of Ford to help give the engine it's smoothness, motion, and torque ( maybe I'm relating this wrong but then maybe not).

All things created equal in rebuilding engines it is no surprise that all engines do not run exactly the same. I always tell my customers these are like kids... as much as you want them to be the same they are not. As far as breaking crankshafts I don't think that's much of an issue with Model A Cranks.... after messing around with these for 35 years I've not personally heard of anyone I know or otherwise who "broke" a crank. There's lots of factors of that including metallurgy, abuse...etc

As I said... personally I can't tell a difference but I do think that the smoother running Model A, idler and otherwise will have the stock flywheel. Again, just my 2 cents worth. Isn't this a great hobby! so many great cars, so many great people!
Thx.
Larry S.
 
Hey Mike K; I LOVE it! Nice work.

Vic: You are an astute thinker!

Chris: I agree with you.

Great thread.
 
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BRENT in 10-uh-C said:
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??
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Hi Brent,
This is getting pretty funny. Eigen functions, huh? That Ouija board is looking pretty good right now. Again, if we were to perform a Fourier Analysis on the rotating assembly, we could come up with an ideal weight for the flywheel/pressure plate assembly. My guess, based entirely on Ouija board consultations would be somewhere between 30 and 36 lbs as an ideal weight for an I-4 of 200 cubic inches and three mainbearings. My own flywheel is 40lbs stand-alone, but the next time I have the engine apart I think I'll try to get it to 36 w/ pressure plate. I have a single channel Fast Fourier Analyser, but you really need a two channel unit to do the necessary calculations... By the way, is your Ouija board single or dual channel?

Happy Thanksgiving to all cranks everywhere - balanced and unbalanced!
 
Now another thought. If a person chooses to lighten a flywheel some will depend on where the weight is removed the most, outboard or inboard next to the crank flange. Just some thoughts about inertia in this whole debate. Rod
 
Rowdy said:
Now another thought. If a person chooses to lighten a flywheel some will depend on where the weight is removed the most, outboard or inboard next to the crank flange. Just some thoughts about inertia in this whole debate. Rod
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I agree. See post #35.

:)
 
Chris in CT said:
. . . I have a single channel Fast Fourier Analyser, but you really need a two channel unit to do the necessary calculations... By the way, is your Ouija board single or dual channel?
Click to expand...

Single channel:
XYEYIqh5QKBFvVd9moFtrG45Hr9TZGNdCu8t02Ak6FhdIDLKZg.jpg

Dual channel:
images


If you have a single channel fast fourrier transform (FFT) device you could still do independent acceleration analysis at different axis points and get a very good data set for good 'ol pencil and paper 3-axis graphing. It would take a while (forget 'fast').

Of course, there will always be 968 1/2 variables unaccounted for in any specific engine build, so perhaps Brent's "Come one, come all.." statement is valid. A multi channel Ouija may be the way to go.
 
I have more layman's questions concerning the energy the flywheel must store and release. At firing impulse on a stock A, the crankshaft flexes torsionally from the energy imparted at the journal and must then "snap back" (and vibrate somewhat torsionally). When it snaps back (primary return pulse), it tries to impart more spin to the flywheel and it also tries to push the rod and piston backwards. Am I right so far? This un-even rotation of the rotating mass (it was already uneven because of uneven rod angularity during each rotation, pressure cycling, etc.) results in another character in the vibration signature. What is the duration of the primary pulse/return pulse? The point in crankshaft angularity when the return pulse will occur increases as rpm rises and will not only change the vibration signature, but will also change the magnitude and timing of the pulses in relationship to the crank's natural frequency. (Harmonics implied.) One of many new thoughts to me, as already stated in this thread, is that the counterweight's mass performs another important function in addition to "counterweighting". (You can't completely counterweight a mass that is part unevenly-reciprocating and part rotating with a purely rotating mass.) That other important function is to reduce crank flex.
It seems to me that the vibration signature would be different for any point it could be measured along the length of the crankshaft. This thread has moved my "theoretical wall" either past my present view or I am against the wall.
 
Jim Huseby said:
I have more layman's questions concerning the energy the flywheel must store and release. At firing impulse on a stock A, the crankshaft flexes torsionally from the energy imparted at the journal and must then "snap back" (and vibrate somewhat torsionally). When it snaps back (primary return pulse), it tries to impart more spin to the flywheel and it also tries to push the rod and piston backwards. Am I right so far? This un-even rotation of the rotating mass (it was already uneven because of uneven rod angularity during each rotation, pressure cycling, etc.) results in another character in the vibration signature. What is the duration of the primary pulse/return pulse? The point in crankshaft angularity when the return pulse will occur increases as rpm rises and will not only change the vibration signature, but will also change the magnitude and timing of the pulses in relationship to the crank's natural frequency. (Harmonics implied.) One of many new thoughts to me, as already stated in this thread, is that the counterweight's mass performs another important function in addition to "counterweighting". (You can't completely counterweight a mass that is part unevenly-reciprocating and part rotating with a purely rotating mass.) That other important function is to reduce crank flex.
It seems to me that the vibration signature would be different for any point it could be measured along the length of the crankshaft. This thread has moved my "theoretical wall" either past my present view or I am against the wall.
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A good point Jim. If you take the reverse impulse moment and apply Chlomondely's grillage coefficient you will see that the forward strake force is cancelled and the engine will run like a top.
 
Well Pete, you got me. I googled Chlomondelly's grillage and got more good info. 'Next time you're in my neighborhood we can go to Chlomon's Delli and Grille. My CCPU may sound smoother after that.
 
I have read this before and I do not who first said it but here it is.


If you are in a hurry you are driving the wrong car.
 
MikeK said:
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.
Ouija-Board-300x200.jpg
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Very amusing, my kind of teacher. Had one applied calculus class in my electronics tech school education. Got really good grades but never had a clue as far as really understanding it. Now almost 72 but back then had a good memory and knew if I got a certain type of problem I knew what the answer should look like. Had I gone on to more advanced math I would have flunked. Nice pictures and explanations Mike, you're obviously very smart but I really appreciate your humor and cut the crap conclusion. Drive and enjoy the Model A. There are numerous aspects to this hobby, something for everyone.
 
A lightened flywheel does affect the idle condition. A stock model a with a heavy flywheel will idle down to 3 - 400 RPM.
The same engine with a lightened flywheel will idle quite slow but not as smooth.
Important to some folks / not so much to others


Dave
 
Very good thread here, lots of correct information.
The one thing, and I may have just breezed by it, is the intended use of the motor combination. The lightened flywheel will be most noticed in the acceleration of the car. Usually this is in conjunction with multiple modifications to increase performance of vehicle. I have been told many things about flywheels, including that a Model A will not run without one.

Keep up the good work, all of this is to be considered in the world of the Model A/B.

Also, if the original Turbo Encabulator article surfaces, I would like to send to some youngsters at work, just to see their reactions.........

John
 
BRENT in 10-uh-C said:
One of the things I always heard growing up in the Model-A hobby was that we wanted a lightened flywheel in our Model-A. Especially if we were going to "tour" with it! The "he said/she said" reasoning that has been associated with this advice seemed plausible to me for years until a few months ago I started analyzing the "what & why" this was needed. A few explanations I have always heard that come to mind are;

#1: The extra weight of the stock-weight flywheel is not good on the rear main bearing as it causes the babbitt to wear faster.

#2: The extra weight of the flywheel makes shifting take longer.

#3: The heavier flywheel makes the engine accelerate much slower.

#4: The roads are different now and we don't need the heavy flywheel like they did back then.

#5: (Add your reason here...)



So this really begs the question n my mind is a lightened flywheel actually better? Well I guess my mindset now after trying a few things on a current project is that it could be, however more than likely it is a "band-aide" to cover up another fault. Let's explore my thoughts and then I would like to hear yours.

Thinking about #1, there is a 3 inch long bearing back there that most engineers would agree is way over-engineered for the task. Just how much extra wear do you suppose 12 pounds of spinning weight makes over the life of the bearing? In other words, exactly how many miles do we suspect the babbitt's life will be shortened? Now granted if someone has a sub-standard babbitt job, then maybe less weight can mask this issue. Maybe the issue is with a flywheel that is 20+/- grams out of balance that is wiping out the babbitt? Yes, a lighter flywheel might prolong the bearing life in this instance but why not correct the root problem?

In considering the number 2 reason, I have heard this but have also found that many drivers actually operate their vehicle with a mindset that defies Henry's original intent of operation. Now granted many Model-A engines must be operated in such a manner to overcome their mechanical deficiencies of low torque or less low-end power but again, choosing to use a lighter flywheel to band-aide those problems such as a worn camshaft or a cam that has the name "Touring" attached to it is in my opinion, doing it for the wrong reason.

One other thought to add, using 600wt transmission oil greatly improves shift quality by slowing the turning gears during clutch operation too however many owners choose not to use the heavier lube for various reasons.

I think many items listed in explanation #2 apply to the reason #3 also. My experiences are that with a stock flywheel and an 'in-specification' original cam (--or one of Bill Stipe's IB330), the acceleration is quite satisfactory due to driving within the engine's torque band. Couple that with a high-compression head and the combination makes a Model-A quite suitable for 95 percent of the traffic flow we typically encounter.

Number 4 is one I have pondered for many years and I have come to realize that it is all in the driver's operational mindset. Over the past decade I have had the privelege of training many Model-A owners on how to drive their newly restored vehicle. The common factor I see out of the majority of these first-time operators is they want to drive it like a sports car by slipping the clutch to take off, making high RPM shifts, and go-kart type steering maneuvers. I show them how the vehicle will effortlessly move away from a stop with the engine idling just by smoothly releasing the clutch pedal. Again, the inertia of the heavier flywheel is a plus. Next the driver typically wants to accelerate to 30mph before attempting to make a low to intermediate gear change. Once they realize that they can accelerate much faster by making their 1st to 2nd gear change at 10mph and using the torque of their engine to propel them, they are usually amazed. They are even more impressed when a 90 degree turn can be made while the transmission remains in high gear. Equally amazing to the veteran hobbyist who drive a Model-A with a 3.54 rear end ratio and negociate the same 90 degree turn without the need for downshifting. Adding to that amazement is when they learn that engine has a stock weight flywheel. Some might even be appauled to hear we are using stock weight flywheels w/ heavier counterweighted crankshafts!!

So my point in this lengthy rant is can someone give me a satisfactory reason why we really should be using a lightened flywheel other than to mask or cover-up some other mechancial deficiency?

.
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The M.E.'s and the mechanical experienced expressed my anticipated response and makes sense mathmatically. A lightened flywheel coupled with a "damper" and balanced crank I believe offers an advantage IF you have a concern for higher RPM's or sustained 55-65 mph of operation. A rebuilt stock motor just went back in my car because that's what I grew uo with and I know I'm going to get another 40-50k out of it. By the way, what does a damper look like installed? I have not seen that one yet. Its all fun stuff. I enjoy seeing the many ideas we come up with to keep our cars on the road.
 
1930marie said:
The M.E.'s and the mechanical experienced expressed my anticipated response and makes sense mathmatically. A lightened flywheel coupled with a "damper" and balanced crank I believe offers an advantage IF you have a concern for higher RPM's or sustained 55-65 mph of operation. A rebuilt stock motor just went back in my car because that's what I grew uo with and I know I'm going to get another 40-50k out of it. By the way, what does a damper look like installed? I have not seen that one yet. Its all fun stuff. I enjoy seeing the many ideas we come up with to keep our cars on the road.
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If an engine is out of balance, it is out of balance at all rpm from one to infinity, not just at 55-65 mph.
You feel the vibration at resonance or harmonics of resonance but the vibration is there at all other rpm's, just to a lessor degree.
Even if you only did parade driving at idle, an engine would benefit from balancing and last longer.

I have a pic of a 12 lb. big block Chev damper installed on a B race engine but can't post it. Probably because the website certificate has not been renewed.
 
johnneilson said:
Very good thread here, lots of correct information.
The one thing, and I may have just breezed by it, is the intended use of the motor combination. The lightened flywheel will be most noticed in the acceleration of the car. Usually this is in conjunction with multiple modifications to increase performance of vehicle. I have been told many things about flywheels, including that a Model A will not run without one.

Yea, the dimwit that came up with that one must have never seen a race car.

Keep up the good work, all of this is to be considered in the world of the Model A/B.

Also, if the original Turbo Encabulator article surfaces, I would like to send to some youngsters at work, just to see their reactions.........

I have a copy of the original article published in the Washington Engineer in 1949.

John
Click to expand...

Pete
 
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