Is a lightened flywheel overrated? (I think so)

[BRENT in 10-uh-C]

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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