That John Deere Exhaust Sound

111 Pratt St. Madison, North Carolina 27025

I read with interest Mr. Doug Seller’s article in the March,
1992 issue of GEM on the firing orders of two cylinder, four stroke
cycle, inline engines. More specifically, why certain two cylinder
engines of this type, such as John Deere, Rumely Oil Pull and
Hart-Parr, had that distinctive appealing exhaust sound, and other
two cylinder in-lines with 360 degree cranks had a very smooth, not
so interesting exhaust sound. This is the first time I had heard of
anyone analyzing the John Deere sound, something I had wondered
about for many years. I recently found a chapter on firing orders
in an old Dykes Automobile and Gasoline Engine Encyclopedia,
twenty-second edition, that states that there are two firing orders
for two cylinder, four cycle, in-line, 180 degree crank engines as
below:

Firing Order No. 1.

Firing Order No. 2

P=Power; E=Exhaust; I=Intake; C=Compression

In example #1 there are two firing or power impulses during one
revolution, that is to say, of 180 degrees each, and in the second
revolution there are no firing impulses at all. According to Dykes,
‘In the second example, if #1 cylinder was on the power (P)
impulse, #2 cylinder would be coming up on its exhaust (E)
stroke.’ It continues, ‘The crank would therefore turn 540
degrees or 1? turns with but one firing impulse.’ This is
misleading, because it implies it is different from the first
firing order when it is not, as far as power impulses are
concerned. Remember each power impulse or stroke takes 180 degrees
or ? turn, back to back, out of that 720 degrees. This applies to
both firing orders.

Apparently the person who wrote the above description of the
second firing order for Dykes was describing firing points on the
circle of rotation and firing impulses, or strokes all in the same
breath. A firing point is a point or location on the circle of
rotation at which time firing is initiated. On the other hand,
firing impulses, or strokes, describe a time or duration of
rotation, such as 180 degrees; therefore, the two firing orders are
effectively identical. The difference is that one starts at a
different location than the other, but still, the exhaust of each
has that same syncopated, appealing sound identified with John
Deere, Hart-Parr, etc. Again in each firing order, the power
strokes both come back to back in one revolution with the next
revolution having no power strokes.

Other two cylinder engines that sound smooth, and less
interesting, have a 360 degree crank with both positions full up or
full down at the same time. The 360 degree crank looks like
this:

The 180 degree crank, as with John Deere, has one piston full up
with the other piston full down and looks like this:

An example of the smooth sounding, two cylinder engine is a
Wisconsin. Here power impulses with this type 360 degree crank, are
evenly spaced throughout the 720 degrees of rotations, thus the
smooth sounding exhaust.

I might add that no two stroke cycle or opposed two cylinder
engines are capable of producing that John Deere exhaust sound with
the possible exception of the Harley-Davidson V-Twin we all admire
so much. That engine has a distinctive exhaust sound, although
somewhat akin to the above 180 degree crank engines, that is
basically unique unto itself.