Burtz Flywheel

J

jeepguy1948

Well-known member
This question is for those that either have or used to have a 31# Burtz flywheel on an unbalanced Model A motor? I have heard some say that a heavier flywheel is better for a non balanced motor and others that say it doesn’t matter.
And while I’m asking questions what does a stock flywheel weigh, 50#?

If stock is too heavy and Burtz is too light, what is considered ideal?
 
Stock flywheel weighs 63 lbs. It is the right size for a stock engine being street driven. Don’t change it unless you understand why you’re changing it and what the trade offs are. A heavier flywheel increases the inertia of the rotating assembly, while a lighter one decreases that inertia. Changing the weight will make some operations easier and others harder.
 
A lighter flywheel will, in theory, allow the engine to spin up and slow down quicker. A heavier flywheel will, in theory, dampen out the inherent vibrations that come from translating up and down motion (the pistons) to rotational motion (the crank). It also dampens the immediate acceleration of the crank when a piston fires and helps maintain the motion as the crank goes through the non-powered portion of its rotation (the mid-stroke periods, and the top of the stroke immediately before the firing on the ignition stroke).

If you are interested in seeing the value of a flywheel, find (or search for) a hit-and-miss engine.

If I was not going to balance the motor, I'd stick with the stock flywheel. Balancing the motor gets rid of many of the vibrations that the heavier flywheel helps absorb. That's what I've done on every stock motor I've built. Henry really did know what he was doing.

I believe that by the time you machine off sufficient metal from a stock flywheel to allow you to mount a V-8 type clutch, you are down approaching the mid-30s in weight. So there really isn't any intermediate.
 
My '28 phaeton has a 16-pound aluminum flywheel with a steel plate against the clutch disk. The engine revs quickly and shifting is faster than with the stock Model A or Model B flywheel, or even a lightened V-8 flywheel, all of which I have tried in the past. The acceleration is also much quicker. Maybe because the phaeton is the second lightest passenger car body style behind the roadster in 1928, but I don't notice any major drawback in idling or while going around a corner at speed, the traditional areas argued against using lightened flywheels in Model A's. If the need arises to downshift while negotiating a corner at speed, it's easy to rev my engine to time its RPMs with the transmission gears' rotation and move the shifter lever to quickly shift gears without grinding. Coming out of the turn after downshifting results in a snappy acceleration to get out of the way of following traffic.
Since you asked about a lightened flywheel versus the stock Model A flywheel, use my aluminum flywheel experience as an opposite extreme. If such a light flywheel makes driving my phaeton more enjoyable and a better citizen in traffic, you won't have to worry about going from the stock flywheel to a Model B or V-8 version. I would bet a sizable percentage of the readers here who do a lot touring have some flavor of lightened flywheel. You will be in good company.
Marshall
 
The crankshaft has torsional vibration all the time due to the acceleration of the pistons and rods. It is worse at certain rpm's.

There is a spot along the length of the crankshaft where the torsional vibration is zero. This is called the node point. The node point with a stock 65 pound flywheel and stock crankshaft is right at the flywheel. That means that you will not feel any torsional vibration. However the crankshaft is still twisting in torsion all the time, it is just that you cannot feel it. The flywheel is not doing any dampening of the torsional vibration, it is just at the node point.

With the lightened flywheel the node point moves forward (towards the front of the engine) so that now the flywheel has torsional vibration. You will feel it now when you drive the car and it will be worse at certain rpm's. With a stiff crankshaft like in the Burtz engine the node point will move further forward but the vibration (twisting) will be less. And the point where the torsional vibration is worse (critical speed) will be at a higher rpm.

A torsional vibration dampener on the front of the crankshaft will absorb a lot of the torsional twisting for the stock crankshaft. It is specifically designed for the stock crankshaft in the Model A. It will somewhat help for a stiff crankshaft like in the Burtz engine but it is not designed for that crankshaft.
 
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I think I sent a private message to nkaminar but really do not know as I just found that I had five messages in my in box that I never responded to! I guess I am not very good with this message thing and apologize to the folks that have sent private messages to me.
 
Richard Knight said:
Still not sure if the message thing is working. As far as I can tell there is no way to check to see if a message was sent?
Click to expand...
On your message interface, you will see a box identifying what you see as "inbox". There is an option to change to "Sent Items".
 

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Neil, what do you think the ideal flywheel weight might be for a Burtz engine and where would that move the node to? As a reminder when folks talk flywheel weight the total number should be considered. Flywheel plus pressure plate plus clutch disc. A stock A has a little over 90lbs at the back of the crank. Bs some what less and then you get into the cut down flywheels and six bolt pressure plate so the weights vary a lot. At what point do you think a dampener should be considered? Thanks
 
The only flywheel where the node point is at the flywheel is the stock one. Any lighter flywheel will move the node point forward and torsional vibration will be felt.

The secret to handling the torsional vibration is in the rear motor mounts. If you have the Float-A-Motor mounts then the bolts through the pads should just be tight enough so that the bolt is snug and cannot move up and down. If you have the original mounts then you need to replace the rubber pads at the frame and use new hardware. After 90+ years the original rubber is hard as concrete and does absolutely no dampening. Even with the Float-A-Motor mounts the rubber pads at the frame should be renewed.

If you are running the original crankshaft then you should use the dynamic dampener. The torsional twisting can be quite severe. If you have the Burtz crankshaft then the dynamic dampener is not necessary and the one designed for the original crankshaft will do little for the stiffer Burtz crankshaft.
 
Thanks Neil, are you implying a stock weight flywheel on a Burtz might be a reasonable thing to do? The Burtz crankshaft is much stiffer than stock but so is s Chevy small or big block or a Ford V8 but they all use dampeners. I have been using floaters for a long time. There are discussions where un equal tightening is discussed. That is a real thing. As you say just tight enough so the bolts are not loose. Earlier floaters might have had one more rubber and washer between the bottom of the mount and the nut. It does make a difference.
 
Even the stiff Burtz crankshaft will have torsional vibration. It is surprising how much twist is generated. The torsional vibrations dampener will help but it has to be designed for the crankshaft. As far as I know there is no dampener designed for the Burtz crankshaft.

The Float-A-Motor rubber pads will get stiff over time and should be replaced if old.

You can run a stock flywheel on a Burtz engine but why. The acceleration with the lighter flywheel is so much better. I have a Burtz engine in my car with his light flywheel and had torsional vibration problems until I adjusted the bolts through my Float-A-Motor mounts and replace the rubber pads at the frame. I can still feel vibration but not so bad that is objectionable. I run a Weber down draft carburetor and a high flow muffler and I am very happy with the performance. I have the Burtz high compression head and his camshaft. I have an over drive and 3.78 rear end. Lots of other changes to the car to make it safe at speed. I can drive down the highway at 65-70 mph but much prefer a leisure pace on the back roads. My car is a heavy 1930 town sedan. 3,000 pounds at the scale at the dump in touring form including tools, spare parts, food, and luggage.
 
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Neil, we are on the same page for the most part. I still would like to have a phone discussion if at all possible. The one thing I don't have at this time is an overdrive. I ran a modified B powered sedan with overdrive for years and thousands of miles. So not having an overdrive is an issue I need to address. I have a bone stock unrestored briggs sedan, a modified B powered Murray, and a burtz powered coupe. I run Stromberg down drafts. This is a topic I am interested in and have heard of some folks switching to heavier flywheels. All three cars have floaters and good rubber.
 
More about torsional vibration dampeners: These are dynamic devices and work like the shock absorbers in your suspension system. The shocks have to be right for the springs and body weight. Too stiff or too soft and the shocks will not work correctly to dampen the springs. In the same way, the torsional dampeners have to have the dynamic response that is right for the crankshaft. Too stiff or too soft and they will not dampen out the torsional vibration. The dampeners have an elastic component and a mass that acts like a miniature flywheel. Both have to be right for the crankshaft in order to dampen out the torsional vibration.
 
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