Here’s a little experiment to determine exactly what the rather controversial Kohler K-series balance gears contribute to the overall reciprocating balance factor in the single-cylinder engine. A K301 is used as the example.
The standard K301 has a reciprocating balance factor (RBF) of 26.8%. This means that the crankshaft counterweights have a mass-moment necessary to cancel 26.8% of the reciprocating force. The intent of the balance gears is to add to the effect of the counterweight force, this being accomplished by proper phasing of the balancers to operate 180 degrees out of phase with the piston motion. To determine the mass-moment (first moment) of each balancer, the following simple test was conducted.
The balancer was supported on a shaft (cam shaft pin) held in a vise, such that the balancer rotated freely. A string (dental floss) was attached and wrapped around the OD of the gear teeth. A small weight basket was fabricated out of a plastic cup and attached to the string. Washers were used as weights. Enough weight was added such that the balance gear mass was held at 90 degrees from the vertical. This is shown below:
Next, this weight, including the cup and portion of the string that suspended the cup, were weighed:
This mass was 75 grams, or .165 lbm. Now, the OD of the gear was measured.
This diameter (tooth to tooth) is 2.48 inches. Dividing by 2, this yields the moment arm that the mass works through, which is 1.24 inches. Multiplying the mass by the moment arm length yields the effective moment of the balance gear which is .205 in lbm.
Force of a rotating mass is a function of the first moment times rotational speed squared. Using 3600 rpm as the speed and doing a little ciphering, each gear contributes 75.5 lbf of force into the system, or 151 lb for the two gears working in phase. The total unresolved reciprocating force (at 3600 rpm) is 703.5 lbf. Thus, the balance gears reduce this by 703.5-151=552.5 lbf, or a 21% reduction.
Calculating a bit further, this can be related to the reciprocating balance factor which is the parameter of interest. The RBF with the gears installed is increased from 26.8% to 49.1%.
Now, bottom line is how much do these balancers reduce vibration that can be felt in the tractor? Transmitted vibration is a function of the mass, orientation of the forces, vehicle design, and system of mounting – a rather complex problem. As most engines are rigidly mounted to the tractor, and the tractor mass becomes part of the stationary system mass, the increase in vibrational amplitude is nill. This exercise in calculating the difference in amplitude will be left for another day. More data from the tractor and engine weight is necessary. The grand conclusion is, due to the rather small contribution these balancers add combined with their unreliable operation and tendency to blast through the side of a perfectly good block when they fail, DON’T REINSTALL THEM DURING AN OVERHAUL.