Lawn Mower: Blade Won't Engage

Some lawnmowers use a belt to drive the blade. This is especially true of mowers with more than one blade. The belt will wear over time and will need to be replaced. It should be inspected at least once per year for wear and signs of age such as cracks. It is wise to replace the belt when you notice that it is worn thin or when it begins to crack. This way you won’t be stuck with a half-mown lawn when the belt decides to fail. If the belt is worn thin you might notice a lack of power when mowing or bagging performance might be poor with clippings left on the lawn. If the belt breaks altogether the engine will run but the blades won’t rotate. Replacing the belt is usually an easy repair. There will usually be a cover over the belt that will need to be removed first. Once the belt is exposed you will rotate the belt around the pulleys and pull the belt off of them. Replacement of the belt is done the same way. If there is more than one blade, then there will also be an idler pulley. In this case make sure to note the routing of the belt around the pulleys before removing it.

If your lawnmower’s blade won’t engage, you might have a faulty blade engagement cable. The blade engagement cable attaches between the blade bail and the blade clutch. The cable is made up of a metal cable with cast metal ends, a plastic sheath, and sometimes a mounting bracket or two. Most problems with the blade engagement cable involve the metal cable itself. The cast ends that connect the cable to to the bail and the clutch are prone to breakage after years of use. The steel cable may fray or break, and this can be accelerated by rust. Another common problem is a kink in the cable. If the cable gets snagged on a shrub or fence, it might be kinked. The kinked metal cable can no longer slide through the plastic sheath smoothly, which can lead to finicky operation or cause the cable to not move at all. If the steel cable becomes badly rusted or corroded, it can seize inside the plastic sheath. This problem is especially common with mowers that are stored in the elements. When water seeps into the plastic sheath it can’t easily evaporate and rust and corrosion will begin. Replacing a blade engagement cable is usually a pretty easy repair. Start by removing any attachment mounts and cutting any cable ties that secure the cable to the mower’s handle. Next, remove the cable from the bail by threading the cast end out of the hole on the bail. Now you can remove the other end of the cable from the blade clutch. You will usually need to tip the mower on its side to do this part. Make sure you tip the mower with the carburetor facing up so fuel doesn’t spill from it. You will likely encounter a cover or two on the underside of the mower that will need to be removed so you can access the clutch. Once the clutch and cable are accessible it is just a matter of removing the cast cable end from the clutch. Install the new cable in the reverse order. Replace any covers you removed to access the blade clutch. Install new cable ties to hold the cable securely to the handle. Finish up by adjusting the cable if necessary. Not all blade engagement cables require adjustment. If yours does, there will be a rotating adjuster on it or a clamping bracket that will clamp the cable’s sheath at the proper adjustment. It is helpful to refer to your owner’s manual for the proper adjustment procedures for you model.

Some lawnmowers are equipped with a blade clutch that allows the operator to shut off the blade while still allowing the engine to run. This handy feature allows the grass bag to be emptied or an object to be removed from the lawn without the need to stop and restart the engine. Blade clutch designs vary greatly between manufacturers, but for the most part each design will consist of a couple of plates or drums that come together when the clutch is engaged. There will be a linkage that brings the sides of the clutch together and usually a brake to ensure the blade is stopped. Most problems with the blade clutch involve the linkage that engages the clutch. There are springs and cables that can break, and brackets that can bend. Over time the clutch plates or drums can wear to the point that they will begin to slip or not lock together at all. The blade brake can wear, which will cause the blade to drift slightly when the clutch is not engaged. Because of the great variation in designs, the steps required to repair a blade clutch also vary widely. In any case, the first step will be to access and inspect the clutch. It will be located on the underside of the mower, above the blade. There will usually be a cover over the clutch that will need to be removed. Some clutches are self-contained and the clutch and its linkage can be removed as a single unit. Others have the clutch under the deck and the linkage is spread out across the mower deck with some components under the deck and others above. When diagnosing the problem look for broken or missing springs, metal shavings or powder that would indicate metal on metal wear, or excessively loose or misaligned parts. Once the problem is diagnosed, the repair should be a simple matter of removal and replacement of the broken or worn components.