There are two reasons that a four cylinder engine is out of balance. So most manufactures went to balancers when they went to higher speeds or horse power. Here are quotes from a engineering book that explain the reasons behind the in-balance.
1) The geometric in-balance:
"An even-firing inline-four engine is in primary balance because the pistons are moving in pairs, and one pair of pistons is always moving up at the same time as the other pair is moving down. However, piston acceleration and deceleration are greater in the top half of the crankshaft rotation than in the bottom half, because the connecting rods are not infinitely long, resulting in a non sinusoidal motion.[improper synthesis?][disputed � discuss] As a result, two pistons are always accelerating faster in one direction, while the other two are accelerating more slowly in the other direction, which leads to a secondary dynamic imbalance that causes an up-and-down vibration at twice crankshaft speed. This imbalance is tolerable in a small, low-displacement, low-power configuration, but the vibrations get worse with increasing size and power.
The reason for the piston's higher speed during the 180� rotation from mid-stroke through top-dead-center, and back to mid-stroke, is that the minor contribution to the piston's up/down movement from the connecting rod's change of angle here has the same direction as the major contribution to the piston's up/down movement from the up/down movement of the crank pin. By contrast, during the 180� rotation from mid-stroke through bottom-dead-center and back to mid-stroke, the minor contribution to the piston's up/down movement from the connecting rod's change of angle has the opposite direction of the major contribution to the piston's up/down movement from the up/down movement of the crank pin."
2) The power pulse cause of in-balance:
"Four-cylinder engines also have a smoothness problem in that the power strokes of the pistons do not overlap. With four cylinders and four strokes to complete in the four-stroke cycle, each piston must complete its power stroke and come to a complete stop before the next piston can start a new power stroke, resulting in a pause between each power stroke and a pulsating delivery of power. In engines with more cylinders, the power strokes overlap, which gives them a smoother delivery of power and less vibration than a four can achieve. As a result, six- and eight- cylinder engines are generally used in more luxurious and expensive cars."
There are ways other than balancers to reduce the vibration but then you have other limits.
Making the block taller so you can have longer connecting rods will reduct the geometric vibration but not the power pulse vibration. The older IH and MM engines are the taller block design.
Making the engine cylinders a "V" shape helps the geometric balance. The Wisconsin engines are the most famous of these.
There is no simple way to counter the power pulse problem without balancers.
So there are the reasons behind the balancers. Why some brands used them and others did not. That was a choice they made on how smooth they wanted their engines to be.
As for JD balanced engines. I much prefer the balancer shafts that the Mannheim/Dubuque engine design utilized(2520,2020,etc) over the Waterloo designed external balancer box in the oil pan.(JD 3010, 3020)
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