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Old 11-21-2020, 12:55 PM   #1
nkaminar
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Default Lightened Flywheel

The Fordor I just bought has a lightened flywheel. It weighs a lot less than the original, maybe 35 pounds. This is the first Model A have owned with a lightened flywheel so I have a question for the group. The engine has a counter balanced crank.

It seems to me that there is more vibration when I back off the throttle compared to previous Model A's have have owned with the stock flywheel. The vibration seems to be torque vibration, not out of balance or another type. I get the same impression when accelerating but not as much. The Model A engine is only 4 cylinders. It seems like the flywheel is fighting with the cylinders.

When running down the road at a constant speed the engine is almost vibration free. It has far less vibration than other Model A's I have owned.

Thanks in advance for your comments.
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Old 11-21-2020, 01:41 PM   #2
1931 flamingo
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Default Re: Lightened Flywheel

Worn universal joint??
Paul in CT
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Old 11-21-2020, 02:38 PM   #3
Gene F
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Default Re: Lightened Flywheel

I thought U-joint too.
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Old 11-21-2020, 02:38 PM   #4
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Default Re: Lightened Flywheel

My 28 still had the multi-disc clutch when I got it. That thing was massive. 63 lbs...
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Old 11-21-2020, 04:04 PM   #5
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Default Re: Lightened Flywheel

Quote:
Originally Posted by 1931 flamingo View Post
Worn universal joint??
Paul in CT
will a stock Model A motor vibrate, going down hill or when you back off the throttle? or is that the u joint?
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Old 11-21-2020, 06:36 PM   #6
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Default Re: Lightened Flywheel

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Thank you all for comments. I had not thought of the U joint.

I jacked up one rear wheel, put the transmission in reverse and the overdrive in low. I can move the wheel back and forth about 1.5 inch at the tread. I hear noises in the differential but not near the transmission (U joint). I think the movement of the wheel is due to the differential gears and perhaps a little bit of slack in the ring and pinon, but it does not seem like there is any issue with the U joint. No noise and it does not feel like there is any movement there.

The car has a high compression head (5.5:1) and stock manifolds and carburetor. It has a high lift and high duration cam and larger valves. All the weight of the flywheel was taken off at the outside diameters so the momentum is reduced more that what would be thought by just comparing the weight with a stock flywheel.

Keep the comments coming.
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A is for apple, green as the sky.
Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.
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Old 11-21-2020, 07:59 PM   #7
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Default Re: Lightened Flywheel

"When running down the road at a constant speed the engine is almost vibration free. It has far less vibration than other Model A's I have owned."

In that case it is not a balance problem. It is the normal vibration of the engine design. You notice it more under certain conditions (off throttle) because the rotating assembly weights have been modified.
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Old 11-22-2020, 06:49 AM   #8
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Default Re: Lightened Flywheel

Changing the weight of the flywheel will have the effect of raising the natural frequency of the engine and drive train. This may or may not be a good thing and will change what is called the "torsional response" of the system. You may have lucked out....but. I would suggest that Henry and Edsel knew what they were doing on the design for the most part. Being a Mechanical Engineer, I would not have the courage to lighten the wheel or change from FORD spec. I do not mean to alarm you but rather to inform.
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Old 11-22-2020, 09:13 AM   #9
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Default Re: Lightened Flywheel

I have a lightened flywheel, 34 lbs, and a v8 clutch and would never go back. The car spools up much faster at a light.
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Old 11-22-2020, 09:43 AM   #10
Bob Bidonde
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Default Re: Lightened Flywheel

The flywheel plays an important role in the dynamic response to the engine's vibrations. When the flywheel & clutch are lightened, the consequences are:
1. Lightening the flywheel & clutch reduces main bearing stresses;
2. Engine acceleration and car braking are improved when the flywheel & clutch are lightened. Torsional impulse stresses in the crankshaft are also reduced. Fuel economy should be a tad better;
3. The flywheel is a gyro that when spinning, it resists changes in its position, especially rotation about the rear engine mounts. Thus its vibration damping quality is reduced when it is lightened;
4. Imagine that the rear engine mounts are the pivot in a seesaw. The engine is on one side of the pivot and the flywheel & clutch are on the other. Vertical vibrations of the engine will be less dampened (more severe) when the flywheel & clutch are lightened. Clutch chatter may become an issue, but in my experience, tightening the front engine support can tune out the chatter.
In short, there are positive & negative consequences to lightening the flywheel and clutch. Personally, I like the positives more than the negatives, so I did it.
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Old 11-22-2020, 09:51 AM   #11
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Default Re: Lightened Flywheel

Faster rpm response was the whole idea about the modification. The problem may also be in the nature of miss alignment. Model A engine to clutch housing fit up has to be right on the money to prevent misalignment with the input shaft of the transmission. Any misalignment will cause binding of the bearings and possible premature failure. Some folks overlook this stuff when building a 4-banger hot rod engine. This is a lot of modification for a fordor sedan. Some of the V8 clutches available are crap too. They might be OK for an 8N Ford tractor but not so good for a car. A rebuild original 9-inch Long type clutch is a much better investment than one of the poor quality reproductions.

The rotating assembly should have been balanced before reassembly. This would include the crankshaft and the clutch & flywheel.
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Old 11-22-2020, 11:21 AM   #12
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Default Re: Lightened Flywheel

The vibration, or sense of vibration can also be attributed to another factor.
The original flywheel was intended to assist in the inertia of the rotating assembly and provide low speed/rpm torque. Think about the roads and conditions back then, mud, snow, dirt roads for the most part unpaved. You needed low speed torque to pull out of many situations.

Now, the lighter flywheel will not absorb nearly as much of the combustion pulses/cycle of the motor. This will make the car/motor feel differently, especially if the modifications of the motor increase the efficiency and power output. You will feel more of the pulsation, after all, you have one combustion stroke per 180 degs crank rotation.

One last thing, the 8N clutch is not nearly enough clutch for a warmed up motor, the truck clutch has counter weights to assist in clamping for on the disk, 8N does not.

J
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Old 11-22-2020, 01:02 PM   #13
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Default Re: Lightened Flywheel

Ok..side note experts. I put in a CW crank and lightened the flywheel about 15 lbs., basically the amount of the crank weights. Since the weight is about the same +/- a few lbs. is the damping effect the same?
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Old 11-22-2020, 02:06 PM   #14
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Default Re: Lightened Flywheel

Short answer is no, it has to do with the Moment of Inertia.

I short, the radius away from the center of rotation has more effect than just the overall weight.

It is a good question though, John
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Old 11-22-2020, 03:17 PM   #15
nkaminar
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Default Re: Lightened Flywheel

Thank you all for the comments. All good ones. I think it answers my original question. It appears that the torsional vibration I am experiencing when backing off the throttle is due to the lightened flywheel, probably half the inertia of the original. It is just not smoothing out the pulses from the pistons.
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A is for apple, green as the sky.
Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.
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Old 11-22-2020, 03:30 PM   #16
Jack Shaft
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Default Re: Lightened Flywheel

The flywheel stores kinetic energy aiding driveability
.Heavy wheel for street,light one for track..Ford determined the ideal weight for stock cars at 63 pounds,B flywheel is 50 lbs to offset the additional counterweights.
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Old 11-22-2020, 07:09 PM   #17
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Default Re: Lightened Flywheel

If you want a complete engineering analysis on what is happening, do a search on this forum by MikeK about torsional vibration. It was about 2 to 5 years ago.
He even had an animated file of a crank assembly under load.
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Old 11-23-2020, 08:39 AM   #18
old31
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Default Re: Lightened Flywheel

Quote:
Originally Posted by Bob Bidonde View Post
The flywheel plays an important role in the dynamic response to the engine's vibrations. When the flywheel & clutch are lightened, the consequences are:
1. Lightening the flywheel & clutch reduces main bearing stresses;
2. Engine acceleration and car braking are improved when the flywheel & clutch are lightened. Torsional impulse stresses in the crankshaft are also reduced. Fuel economy should be a tad better;
3. The flywheel is a gyro that when spinning, it resists changes in its position, especially rotation about the rear engine mounts. Thus its vibration damping quality is reduced when it is lightened;
4. Imagine that the rear engine mounts are the pivot in a seesaw. The engine is on one side of the pivot and the flywheel & clutch are on the other. Vertical vibrations of the engine will be less dampened (more severe) when the flywheel & clutch are lightened. Clutch chatter may become an issue, but in my experience, tightening the front engine support can tune out the chatter.
In short, there are positive & negative consequences to lightening the flywheel and clutch. Personally, I like the positives more than the negatives, so I did it.
Bob, very well said.
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Old 11-23-2020, 08:48 AM   #19
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Default Re: Lightened Flywheel

Why would you have a Light flywheel, Cam, Big Valves, High compression head and run stock manifolds and carb? You are leaving the real value of all those modifications on the table IMO. I know you just purchased it, bet the previous owner kept the carb and manifolds? Get manifolds and downdraft asap! You will not regret it. Of course, after you get your knock sorted! Good luck.

Last edited by Nosetime; 11-23-2020 at 09:27 AM.
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