Mid-mount mowers for lawn, garden and compact tractors typically have (two or) three blades and are designed for quality mowing of turfgrass (Figure 1). They are not designed to cut tall, weedy grass. They have multiple gage wheels and rollers that allow a relatively low cutting height with minimal scalping.
Height of Cut
Height of cut with a mid-mount mower is controlled in one of two ways. On most smaller lawn and garden tractors, the mower deck is suspended from the tractor lift linkage and the deck does not ride on the gage wheels. There is a dial or some similar adjustment on the tractor that limits how far the linkage will allow the deck to drop and thus sets the cutting height. When the operator moves the lever to drop the deck, it stops at the preset level and holds the deck suspended. On units like this with a suspended deck, the gage wheels do not normally ride on the ground and serve only to prevent scalping.
On many sub-compact and compact tractors, the mid-mount mower deck is dropped all the way down in use and rides on the gage wheels (which control the height of cut). On these “ground following” mower decks, the deck is merely pulled along by a linkage between the front of the deck and the front of the tractor and is not suspended when in use.
Adjusting Height of Cut
With a suspended deck, you adjust the height of cut by setting the dial or other mechanism on the tractor. With a “ground following” deck, you set the height of cut by adjusting all four gage wheels to the same height setting. This might involve moving a pin at each wheel or moving a stack of spacers at each wheel. Your operator’s manual will explain how to set your specific deck. To measure the height of cut, park the mower deck on a smooth, level (preferably paved) surface, lower the deck, and measure the distance from the ground up to the cutting edge of the blades (be sure the tractor engine is turned off). This measurement should be the same for all blades.
It may come as a surprise to you that the deck should not be run level. With any rotary mower, it is desirable to set the front slightly lower so the blade cuts at the front, and the rear of the blade does not recut the grass or drag on the grass. This will reduce the power requirement and provide a cleaner cut. Your operator’s manual will tell you how to adjust your mower to achieve the correct “nose down” position.
Side to Side Level
A mower deck also must be level from side to side. You can check your deck by lowering it and measuring the height from the ground to the cutting edge of the blade on each side with the blades turned at a right angle to the direction of travel (be sure the tractor engine is turned off).
Adjusting Anti-scalp Rollers and Gage Wheels
Most mid-mount decks have two or more anti-scalp rollers that must be adjusted for height of cut. You will need to adjust the gage wheels on suspended decks, too. All of these components should be adjusted so that they do not contact the ground when the deck is lowered to the preset cutting height and the mower is parked on level pavement. Your operator’s manual will give specific instructions on adjusting these components.
Different manufacturers recommend different ground clearances, but ¾ inch is fairly typical. These components will then lift the mower deck when a high spot is encountered, but it will have no effect on level ground. Furthermore, proper adjustment will reduce wear on the wheels and rollers since they will normally not be contacting the ground.
Adjusting a mid-mount mower is more complicated than some other types of mowers, but once it's adjusted, you shouldn’t need to change the adjustments unless you change the cutting height. These adjustments will contribute significantly to both the quality of cut and the longevity of your mower.