Learning how to remove blades from bush hog mowers is one of those chores that every tractor owner eventually has to face, usually right when the grass is growing faster than you can keep up with. It's never exactly a "fun" Saturday afternoon project, but if your mower is starting to leave streaks of uncut grass or vibrating like it's trying to shake itself apart, it's time to get under there and swap those dull blades out. Most people dread this job because these bolts are notorious for being seized, rusted, and generally stubborn, but with the right approach, you can get it done without losing your temper or your knuckles.
Getting your gear together first
Before you even think about crawling under that deck, you need to make sure you have the right tools. Trying to do this with a standard adjustable wrench is a recipe for disaster. You're going to need some serious leverage. Most Bush Hog brand mowers use a pretty large nut—often around 1-1/2 inches or 1-11/16 inches—so check your specific model before you start.
A heavy-duty impact wrench is your best friend here. If you have a high-torque pneumatic or cordless impact, use it. It'll save you twenty minutes of straining. If you don't have one, you'll need a long breaker bar and probably a "cheater pipe" (a length of steel pipe to slide over the handle for more leverage). You'll also want a large flat-head screwdriver or a putty knife to scrape away the baked-on grass and mud, a block of wood to wedge the blade, and some penetrating oil like PB Blaster or Liquid Wrench.
Safety is the most important part
I can't stress this enough: safety is everything when you're working on farm equipment. Before you even touch a wrench, make sure the tractor is turned off, the key is in your pocket, and the PTO shaft is completely disconnected. You don't want any freak accidents.
Since you'll be working underneath the deck, you need to get the mower off the ground safely. If you're using the tractor's 3-point hitch to lift it, do not trust the hydraulics to hold it up while your hands are near those blades. Always use heavy-duty jack stands or solid wooden blocks to support the weight of the deck. I've seen hydraulics fail, and it happens fast. Give the mower a good shove once it's on the stands to make sure it's rock solid before you reach underneath.
Accessing the blade bolts
Most modern rotary cutters have an access hole on the top of the deck. This is a lifesaver. Instead of trying to swing a massive wrench while lying on your back in the dirt, you can just align the blade nut with that hole and work from the top.
If your mower doesn't have an access hole, you'll be working from underneath. This is where things get messy. Scrape away all the old grass and dried mud from around the bolt head and the nut. If you can't see the metal, you aren't going to get a good grip with your socket. Once it's clean, soak that nut in penetrating oil. If it looks particularly rusty, let it sit for twenty minutes. Go grab a coffee or a Gatorade; let the oil do the hard work for you.
Breaking the nut loose
Now comes the part where you actually find out how much the previous owner (or past you) over-tightened things. If you're using the access hole, drop your socket through the top onto the nut. Underneath the deck, you'll need to wedge a block of wood between the blade and the side of the mower deck. This keeps the blade from spinning while you're cranking on the bolt.
If you're using an impact wrench, give it a few bursts. Usually, the vibration and torque will pop it loose pretty quickly. If you're using a breaker bar, this is where you'll need some muscle. Remember the old "lefty-loosey" rule—most Bush Hog blades use standard right-hand threads, so you'll be turning it counter-clockwise to loosen.
If the nut refuses to budge, don't just keep pulling until you round the corners of the nut. Hit it with more oil. If it's really stuck, a little bit of heat from a torch can expand the nut just enough to break the rust's grip. Just be careful not to overdo it and damage the seals in the gearbox.
Dropping the blades and inspecting the hardware
Once the nut is off, the blade and the bolt should drop out. Be careful—those blades are heavy, and even a dull one can give you a nasty bruise if it lands on your foot. Take a second to look at the blade bolt and the washer.
Bush hog bolts have a "D-shape" or a shoulder that fits into the blade bar to keep them from spinning. If that shoulder is worn down or the threads look stretched and thin, don't try to reuse them. It's a lot cheaper to buy new bolts than it is to replace a gearbox because a blade flew off at 500 RPM. Also, check the "stump jumper" (that big round plate the blades are attached to). If it's cracked or badly bent, you've got bigger problems to deal with.
Cleaning and prepping for the new blades
Since you already have the mower up and the blades off, this is the perfect time to give the underside of the deck a thorough cleaning. All that packed-on grass holds moisture against the metal, which leads to rust and eventually holes in your deck. Scrape it down to the metal if you can.
Before you put the new blades on, I always recommend putting a little bit of anti-seize lubricant on the threads of the bolts. You will thank yourself immensely the next time you have to do this. It prevents the nut from rusting onto the bolt, making the next removal a five-minute job instead of a two-hour ordeal.
Installing the fresh blades
When you're putting the new blades on, make sure they are facing the right way. It sounds silly, but people put them on upside down more often than you'd think. The "lift" or the slanted part of the blade should be pointing up toward the deck, not down toward the ground. The sharp edge needs to be trailing in the direction of rotation.
Hand-thread the nut onto the bolt first to make sure you aren't cross-threading anything. Once it's on there straight, use your block of wood again to jam the blade, this time on the opposite side so it doesn't spin while you tighten.
You want these nuts tight. Check your manual for the specific torque specs, but usually, we're talking about 400 to 450 foot-pounds of torque for the big ones. If you don't have a torque wrench that goes that high, you're basically looking for "as tight as you can get it with a long breaker bar." If you used an impact wrench to take them off, you can use it to zing them back on, but always give them a final check with a manual wrench to be sure.
Final checks before mowing
Once everything is tightened down, remove your blocks of wood and your jack stands. Lower the mower back to the ground and reconnect the PTO shaft. Before you head out into the tall field, engage the PTO at a low idle. Listen for any weird vibrations or clanking sounds. If everything sounds smooth, you're good to go.
Knowing how to remove blades from bush hog equipment is a basic skill that saves you a lot of money at the repair shop. It's a dirty, sweaty job, but there's a certain satisfaction in seeing that clean, even cut across a pasture once you're done. Just take your time, use the right tools, and always keep safety at the front of your mind. Now, go get that grass cut!