That John Deere Exhaust Sound

The 180 degree crank

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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.

Cylinder no.

1

2

1st revolution

P

C

1st revolution

E

P

2nd revolution

I

E

2nd revolution

C

I

Firing Order No. 2

Cylinder no.

1

2

1st revolution

P

E

1st revolution

E

I

2nd revolution

I

C

2nd revolution

C

P

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.