Is a lightened flywheel overrated? (I think so)

[Marco Tahtaras]

Originally Posted by MikeK

I guess (and I do mean guess!) it depends on where you want the crank to break. The traditional place is for the rear to snap off.

I'm sure there are examples to the contrary, but the ONLY broken cranks I've seen were improperly reground. I still have a Burlington crank on the shelf for a future project however.

[SteveB31]

It has always been my understanding that we remove the weight off the flywheel BECAUSE we add the weights on the crankshaft to counter balance the crankshaft (like Ford did on the later B motors). Therefore, we still have the SAME amount of total weight (crankshaft + weights + flywheel) like Ford did (they reduced the flywheel weight when they added weight to the crankshaft).

Your thoughts?

[denis4x4]

I buy SteveB31's idea that the weight is still the same, just rearranged. Too, my car with the lightened flywheel and a counterweighted crank is probably 400 to 500 pounds lighter than a stock Model A.

[Mike V. Florida]

I think this thread is great!! We have various opinions alot of facts, and not a single one is personal. As a matter of fact I see where the posters are going out of their ways to see that nothing posted is personal in nature!

[Kohnke Rebabbitting]

Mass does Matter, the rear main on a Model A has always be a strong point with Factory Babbitt, of the three bearings, except where the Babbitt has been replaced by incompetence.

The rear bearing is not the one that catches the most wear, it is the center Bearing, and the crank Bows from the heavy weight of the flywheel.

Just about every crank that has had a lot of miles will measure out about the same wear, on both ends, and the center will measure about 3 times more from the crank running bowed.

Get rid of the weight, and get rid of some of the wear.

[Purdy Swoft]

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Originally Posted by ursus

I have heard a few others say that the smoothest running engine of this lineage was the Model B engine with pressed on counterweights. These weights were added on to the earlier uncounterweighted Model B crankshafts when such engines were returned to Ford for rebuilding. Ford reassembled these with the stock flywheel, thus making the assembly heavier than the stock counterweighted assembly. Ford must have thought this was OK.

The original flywheel that was used with the first year model B engines with uncounterweighted crankshafts were not the same as model A flywheels. All of the model B flywheels were lighter than model A flywheels as far as I know. I have one of the flywheels that was used with the early B engine on my roadster. I didn't record the weights at the time but the clean B flywheel without the ring gear was 20 lbs. lighter than the flywheel that I removed from my A . I meant to re weigh the B flywheel after I installed the new ring gear . In my exitement To get the engine together I forgot . The ring gear probably weighs around 4 lbs. . If this is the case my flywheel would be around 16 lbs lighter than a model A flywheel . The engines in two of my cars have similar mods, same head, cam and both run dual up draft B carbs. One has a B flywheel and the other has a stock model A flywheel. The one with the B flywheel has better throttle response and accelerates faster than any model A that I have ever driven. The gears shift smoother than any model A that I have ever driven. I am convinced that if a flywheel is properly lightened and balanced, low and mid range performance will increase. A hevier flywheel may actually have a higher top end speed. I'm more concerned with low and mid range power than cruising at 65-70 mph. I've had the A flywheel car up to 75 mph going up hill picking up speed. I still prefer the lighter flywheel.

[tbirdtbird]

Alas, no one chimed in on the part where you teach modern drivers how to drive the darned thing. Today's drivers have no clue about what a long-stroke motor is and all the low end torque that gives them. Don't need to rev to 4K each shift and have a 6-speed box to get somewhere. Those extra gears are needed because the low end torque of a modern motor does not exist

[eagle]

As I see it, the trouble with the "quicker spool up" theory is that few pounds less of spinning mass is going to make the mass of my whole car speed up faster? Don't buy it, although maybe with the car not in gear... I also agree with the description Brent gave of driving. "Shift early, not often" Thats my theory. Some people nearly blow their gaskets over the "lugging" issue. I've heard people say " I'm not grinding the gears, thats just a little clicking on the way in" Yeah right, shift early and no more "clicking".

[BILL WILLIAMSON]

Originally Posted by tbirdtbird

Alas, no one chimed in on the part where you teach modern drivers how to drive the darned thing. Today's drivers have no clue about what a long-stroke motor is and all the low end torque that gives them. Don't need to rev to 4K each shift and have a 6-speed box to get somewhere. Those extra gears are needed because the low end torque of a modern motor does not exist

Tbird,
Excellent thoughts! It's so easy to get caught up in faster & quicker is better & if we do this mod & that mod, our engines will last better than Ford designed it. Is some of our "engineering"? better than Ford's? With proper driving & good maintenance, a Model A, in stock form, will deliver MANY miles of good service.
I sold my '30 coupe that would run 80 MPH with all stock drive train & 19" wheels, it WAS fun. Now back to my bone stock '29 coupe for a new experience in driving it as Ford intended. It has sufficient power & speed for city & country driving, with the exception of freeway trips. I'll endure the typical buzzing/vibrating, etc, just to keep it as it was designed. I cheated a little, It has 16" wheels & a dandy Zip-A-Rak telescoping luggage rack! Bill W.

[John LaVoy]

When I was working on my first Model A restoration for a tour car I located a machine shop in Southern California. The shop was owned and operated by a man named Kong. He did land speed runs in a drop tank racer in the late 1940s. I had him add counter weights to my model A crank. He said that I needed to lighten the flywheel to assist with acceleration and that you should remove at least as much weight as you added to the crank. He cut my fly wheel to 34 pounds. I figure he must know what he is talking about regarding the reduction in weight of the flywheel since he had been racing on the salt with Model A and V-8 flat heads and setting many records.

It so happens his car was on display with my new Roadster Pickup in the Ford booth at the recent SEMA show. The drop tank racer has his name painted on the side of the car. I thought it was something since the crank used in the pickup was one of the cranks I had him do in 1964, I had a couple done and never used one until now.

[PC/SR]

Interesting thread. My pal Jerry and I used to drive the fire and logging roads of Northern California in his A coupe before either of us had a drivers license. That stock flywheel was great for doing 3, 4, 5 mph over ruts and all. That coupe even had a 4 speed transmission. Man, we could idle over those ruts.
50 years later I could not drive my speedster with a lightened flywheel on those kinds of roads, but I do like it on FAST hill climbs.
I doubt that in ordinary driving anyone but an experienced driver could tell the difference between a lightened and regular flywheel.
High school physics, as ArtDeco noted, and experience confirms, that you will "store" more energy in a heavy flywheel and that will make a difference in the rpm drop, or rise, between a 15 and a 20 mph shift point, but you will hardly notice it. Except that is one of the reasons you do not need to double clutch to shift up but do to shift down.
Shifting early, not often, at low rpm, is permissible, even desirable, in an A not so much because of flywheel weight, but because the stock camshaft profile produces low end torque and a high volumetric efficiency at low rpm, and that has little to do with flywheel weight except that it maintains rpm at the shift point, whatever it might be. You cannot efficiently shift to 2nd at 10 mph with a so called touring cam, no matter what the flywheel weight. Nor can you idle comfortably to 400 rpm with a 35 lb flywheel.
Whether a lightened flywheel is "overrated" depends on your use. If you drive steady speed, or ordinary tour and club driving at whatever speed, the stock flywheel is fine, no matter what speed equipment you have.
If you want to race, really push it, get a lightened wheel.

[gwhite]

Originally Posted by John LaVoy

When I was working on my first Model A restoration for a tour car I located a machine shop in Southern California. The shop was owned and operated by a man named Kong. He did land speed runs in a drop tank racer in the late 1940s. I had him add counter weights to my model A crank. He said that I needed to lighten the flywheel to assist with acceleration and that you should remove at least as much weight as you added to the crank. He cut my fly wheel to 34 pounds. I figure he must know what he is talking about regarding the reduction in weight of the flywheel since he had been racing on the salt with Model A and V-8 flat heads and setting many records.

It so happens his car was on display with my new Roadster Pickup in the Ford booth at the recent SEMA show. The drop tank racer has his name painted on the side of the car. I thought it was something since the crank used in the pickup was one of the cranks I had him do in 1964, I had a couple done and never used one until now.

Charles "Kong" Jackson?!?!? Wow!

[MikeK]

Originally Posted by gwhite

Charles "Kong" Jackson?!?!? Wow!

Lotsa A and early V8 speed stuff marked KONG out there. Here's a thread from our twisted sister, the HAMB. Scroll down to post #37. KONG

Interesting how this thread is progressing, now through testimonials. All BRENT's fault, posting intelligent questions!

[Jim/GA]

Originally Posted by SteveB31

It has always been my understanding that we remove the weight off the flywheel BECAUSE we add the weights on the crankshaft to counter balance the crankshaft (like Ford did on the later B motors). Therefore, we still have the SAME amount of total weight (crankshaft + weights + flywheel) like Ford did (they reduced the flywheel weight when they added weight to the crankshaft).

Your thoughts?

When it comes to rotational inertia of a rotating system (also known as moment of inertia), not all mass added or removed from the system is the same. It also depends on the SQUARE of the distance that mass is from the center of rotation.

Here is a simple example:

1 lb. of mass that is removed 10" from the center of rotation (1*10*10=100 lb-sq.in.) is equivalent to 4 lbs. of mass added to a point 5" from the center of rotation (4*5*5=100 lb-sq.in.) to maintain the same total rotational inertia of the system.

So, to remove as many pounds from the flywheel as you add to the crank in counterweights is probably over correcting by quite a bit, because the counterweights added are probably closer to the crankshaft main bearing centers than the weight you removed from the flywheel. You need to keep track of where you are removing and adding the weight.

This is classical mechanics.

[Marco Tahtaras]

Originally Posted by Jim/TX

When it comes to rotational inertia of a rotating system (also known as moment of inertia), not all mass added or removed from the system is the same. It also depends on the SQUARE of the distance that mass is from the center of rotation.

Here is a simple example:

1 lb. of mass that is removed 10" from the center of rotation (1*10*10=100 lb-sq.in.) is equivalent to 4 lbs. of mass added to a point 5" from the center of rotation (4*5*5=100 lb-sq.in.) to maintain the same total rotational inertia of the system.

So, to remove as many pounds from the flywheel as you add to the crank in counterweights is probably over correcting by quite a bit, because the counterweights added are probably closer to the crankshaft main bearing centers than the weight you removed from the flywheel. You need to keep track of where you are removing and adding the weight.

This is classical mechanics.

I was going to comment similarly but you beat me to it! Several folks have mentioned "total weight" without regard to the distance of that weight from the axis.

[Patrick L.]

How much is actually usually added to a 'weighted' crank ?? It seems I've always heard and read that about 20# 'must' be removed from the wheel when the crank is ' weighted' .. Physics is physics and 'arm' [length] is everything isn't it ?? My girlfriends have always said that anyway..

[Pete]

Originally Posted by MikeK

Lotsa A and early V8 speed stuff marked KONG out there. Here's a thread from our twisted sister, the HAMB. Scroll down to post #37. KONG

Interesting how this thread is progressing, now through testimonials. All BRENT's fault, posting intelligent questions!

Thanks for the link Mike. Brought back a lot of memories.
I talked to Kong at Bonneville several times and had one of his 2 coil ignitions on one of my engines. That was probably the finest battery ignition there ever was for a flathead.

[Paul from Maine]

I agree with you on every point. However, I would like to point out that in #4 you mention upshifting from 1st to 2nd at ten mph. Try shifting from 1st to 2nd at ten feet, not ten mph. No need to to double clutch, no need to wait for gears to slow down in the tranny, no gear grinding, an instant shift, and quick get away because of that 60 plus pound flywheel! Got that technique from a late twenties issue of Popular Science. I was skeptical until I tried it myself. The article also recommended shifting from second to high as soon as possible without lugging the engine. Again no need to to double clutch, no need to wait for gears to slow down in the tranny, no gear grinding, an instant shift, and quick get away because of that 60 plus pound flywheel! Let the criticism and naysaying begin!

[dumb person]

Another thread was discussing replacing the rear main bearing in the car. That reminded me of this thread. If you removed the rear main bearing would the weight stress the gearbox input shaft and bow the crank down a little until the bearing was replaced?

[Craig Lewis]

Originally Posted by Patrick L.

How much is actually usually added to a 'weighted' crank ?? It seems I've always heard and read that about 20# 'must' be removed from the wheel when the crank is ' weighted' .. Physics is physics and 'arm' [length] is everything isn't it ?? My girlfriends have always said that anyway..

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!