Lawn Mower: Cuts Grass Poorly

A perfectly manicured lawn starts with a properly maintained lawnmower blade. A sharp blade cuts each blade of grass cleanly, which allows the grass to heal quickly. When grass is cut with a dull blade the grass is torn, leaving a ragged and large wound on each blade. The grass takes longer to heal, which can allow disease into the lawn. The blade on your mower should be inspected at least once a year and sharpened or replaced as needed. Your lawn will actually tell you when your blade needs to be sharpened if you know what to look for. When a lawn is cut with a sharp blade the grass blades will heal quickly and only about 1/32” to 1/16” of the tip will turn brown. When the grass is cut with a dull blade the grass is torn and takes much longer to heal, often causing 1/8” or more of the tip to brown. Performance is another benefit of a sharp blade. A sharp blade requires less power to cut through the grass. This results in better engine efficiency, faster blade speeds, and longer engine life. Mulching blades require more frequent inspection and maintenance. When mulching, the grass is cut and then the clippings circulate around the mowers deck, being cut over and over until they finally fall from the deck and settle back into the lawn. Much more power is required from the engine as the clippings are sliced over and over. A sharp blade is essential for keeping the engine from bogging down. A dull blade will not cut the clippings as finely as a sharp blade, causing the mower to leave clumps of grass on the lawn. Another cause of poorly cut grass is a damaged blade. If the blade strikes something solid such as a rock, tree root, or a buried pipe, the blade can be badly bent or even cracked. In addition to cutting the grass poorly, a damaged blade can be dangerous. A bent blade will often vibrate badly, which can cause additional damage to the mower. A bent blade might even strike other parts of the mower. A cracked blade can break at any time, sending the broken piece flying away from the mower. Replacing your mower blade is a simple repair. Start by tipping the mower so you can access the blade. The mower should be tipped so the carburetor is up, otherwise fuel will spill from the carburetor and onto the ground. Mowers with vented gas caps may need to have the fuel drained out of the fuel tank first or fuel will spill from the cap. This is especially important with newer models that have a charcoal filter in the cap. If fuel gets into the charcoal filter, the cap will no longer vent properly and it will need to be replaced. Once the mower is tipped, the blade can be removed. The blade will be held in place by one or two nuts or bolts, depending on the model. Use a socket wrench to remove these fasteners. Often the blade will rotate when you try to remove the blade with your wrench. If so you can bind a piece of scrap wood between the blade and the mower’s deck so the blade cannot rotate. There will often be washers or a plate between the fasteners and the blade. Take note of the order of any washers or plates so they can be reassembled in the correct order. When installing the new blade, make sure you mount it with the correct side up. The bevels where the blade is sharpened should go up, towards the mower’s deck. Many blades are even stamped “This side towards grass” on the bottom, to help you get the blade mounted correctly. Replace the fasteners and any washers or plates and hand-tighten. Most blade fasteners will need to be torqued to a specific spec. This value can be found in the owner’s manual. A helpful tip is to write the torque value on the mower’s deck so you don’t need to look it up each time you service the blade. Once you have the torque value, use a torque wrench and tighten the blade fasteners. Again, use a scrap of wood if needed to bind the blade while tightening the fasteners. Keeping a sharp blade on your mower will keep your lawn looking great and help to make your mower last for years.

You might not think so, but the deck on your lawnmower plays a huge part in how good your lawn looks. The lawnmower deck is carefully engineered for optimum airflow to guide the grass after it is cut. When bagging the deck guides the grass into the bag quickly so it doesn’t fall back to the lawn or clog the deck area or the bag chute. When mulching the deck helps to recirculate the clippings so they get cut over and over until they are fine enough to fall back down into the lawn. The design of the deck also works with the blade to create lift, standing up the grass blades after being cut. Most quality of cut issues concerning the deck are caused by grass building up underneath the deck. Once enough grass builds up the deck can’t function as it was designed and the quality of cut suffers. The wetter the grass the faster and thicker it will build up. It is a good idea to occasionally check the underside of the deck for buildup. The buildup can be easily removed by scraping it off with a stiff putty knife. Most lawn mower decks use various baffles underneath to guide air and clippings. Sometimes the baffles are welded right to the deck, other times they bolt or screw in place. If the baffles are missing, rusted through, or otherwise damaged the air flow will be affected and the quality of cut may diminish. If a damaged baffle is welded right to the deck you will likely need to replace the entire deck in order to once again get the quality of cut you expect. If the baffles bolt or screw in place the repair will be a simple matter of removing the damaged baffle, cleaning the area where it mounts, and bolting a new baffle in place. Rust damage can also affect your mower’s quality of cut. After years of use rust can damage the deck to the point that it rusts through in places. This damage not only affects the quality of cut it can also be dangerous. Any hole in the mower deck can let rocks, chunks of wood, or other debris go flying from the mower. These projectiles can cause serious injury or even death if they hit somebody. The mower deck should be immediately replaced if it has any holes in it. Cleaning the deck and inspecting it for damage might just be all it takes to once again make your mower a perfect lawn manicuring machine.