In the early part of the twentieth century, virtually all flywheels were of the spoke type. There seem to be two reasons for this. The first is that given the technology of the day, it was easier from a metallurgical and engineering standpoint to keep a spoke flywheel from cracking than it was a solid disk. The second is that with the engines of the day being mostly one or two cylinders and relatively slow speed, a spoke flywheel tended to break up harmonic vibrations rather than carry them. Thus when the first John Deere model “Ds” were produced, they had 26-inch diameter flywheels.
It wasn’t long before it was realized that this flywheel was causing a problem the engineers who tested this tractor hadn’t discovered; in certain instances when the front wheels were turned to the left and the left front wheel went over a bump or obstruction, the wheel made contact with the flywheel. So the diameter of the wheel was reduced to 24 inches.
However, it was learned that spoke flywheels were somewhat of a safety risk. This, coupled with some cracking problems particularly when Mr. Mechanic got a little aggressive when removing it, caused Deere to introduce a new flywheel. By now, whatever technological limitations caused Deere to stick with spoke flywheels on the early “Ds” seemed to have been overcome and the new unit was of solid design. The new flywheel retained the same part number as the old spoke wheel and otherwise the last “spoker Ds” and the first solid flywheel “Ds” are identical. What makes these first solid flywheels special or different from those on later tractors is that the holes at the end of the stress slot are 7 /8ths inch in diameter, or about the size of a nickel. These tractors, beginning in December of 1925 with serial number 36249, are today commonly known as “nickel hole flywheel Ds.”
It seems, though, that Deere still hadn’t completely perfected the art of flywheel building because it wasn’t very long before it was discovered that the new solid flywheels also had a propensity to crack. So on March 9, 1926, a decision was made to lengthen the stress slots from 4-1 / 2 inches to 5-1 / 4 inches and increase the diameter of the holes from 7 /8 inch to two inches. A slight change was also made in the taper of the flywheel and reinforcing ribs were added.
Several conjectures have been made about when the change occurred. One school of thought
is that the change occurred at serial number 38285 with a few tractors after this number being built with “nickel holes” to use up excess inventory. Other evidence supports a change at 38692. In either case, fewer than 2,500 model “Ds” with these unique features were built and after they began to exhibit cracking problems, a program that replaced them with the two-inch hole flywheels for free was implemented. This, of course, means that very few of these tractors made it intact to the time when we all started looking for them.
When the model “D” was given more power for 1928, one of the updates was a new splined crankshaft and flywheel replacing the old keyed design.