Lawn Mower Blade Bolt Stuck

I know the feeling, FRUSTRATION!!! but we'll get it figured out. The blade bolt can be stuck for a few different reasons, usually it's a combination of rust and over-tightening.

The easiest way to remove a stuck blade bolt is with an impact tool, they make the whole job look easy.

Other Options include:

  • Use Tool Leverage
  • Vice-grips
  • Hammer & Chisel
  • Heat
  • Welder

You may not have an impact, so I'll show you a few different options. Some of these options may not suit you, it'll depend on what tools you have access too.

Best to don a pair of work gloves, stuck bolts usually means slipping tools. 

air impact tool

Impact Tool

The impact tool is designed for this job.

Over-tightening The Bolt

Mower blade torque spec

Blade Bolt Torque

Mower blade bolts should be torqued to spec, these bolts are usually over-tightened and when you add corrosion, removing can be a headache.

mower blade bolts

L/H or R/H

A l/h threaded bolt loosens to the right. (left bolt in pic)

A r/h thread loosens to the left. This is the most common type thread. (right bolt in pic)

Removing A Rounded Bolt

Over-tightening is common. Mower blades are designed to be tightened to a specific torque, which isn't as tight as you might expect. That's because they're designed to slip if they hit a solid object. The slipping protects the engine from serious damage associated with a kerb stone strike.

 

Also common is turning the bolt the wrong way, hey, could happen a bishop.

All single blade walk-behind mowers will have what's known as a right hand thread. That means, to loosen the bolt, you turn it to the left.

 

Only some large twin blade walk behind mowers and lawn tractor mowers are likely to have one left hand threaded blade, and the other a right hand thread.

How do you know which is which? (The following info is written with the mower deck viewed on it's side.)

 

Simple, if the blade is designed to cut turning left, then it will be a right hand thread, this is the most common type. To loosen a right hand thread, you turn it to the left.

 

The same idea applies to twin blade tractor mowers. A left hand thread is common on lawn tractor mowers with rear discharge and collector. So, viewing the deck on it's side - if the blade cuts grass turning to the right, it's a left hand thread, to loosen a left hand thread, turn it to the right.

 

Typical torque specs for blade bolts are anywhere from 35 ft lbs to 90 ft lbs, you'll need to check the spec of your mower, it's important to get it right.

 

Most of the time blade bolts just get buttoned up tight and aren't torqued to spec, and that's OK, but you run the risk of bending the crankshaft if you hit a solid object. I advise using a torque wrench, it's a lot cheaper than a new mower engine.

 

Torque wrenches are easy to use, they come in inch pounds for smaller torque specs, but for mowers you'll need foot pounds. A torque wrench from 30 to 100 foot pounds is about right.

 

If you don't have or can't borrow one, check out this post on my 1/2 drive Teng Torque,it won't break the bank, it covers 30 to 150 ft lbs, it's simple to use, calibrated from factory and has a flexible working range.

 

I get my torque wrenches calibrated every year but it gets a lot of use. If you set your torque wrench to zero after you use it and don't throw it around, it should stay calibrated for years.

 

 

A rounded bolt head is a real pain in jacksie. It usually happens when the bolt is old and corrosion has deformed it. Worn or damaged tools will give you the same result.

 

It can also happen if the wrong size tool is used. As you know American mowers use imperial size nuts and bolts, but if your mower is European or Asian, it will likely be metric sizes.

 

Trouble is you can get a imperial wrench to fit a metric bolt, but it's loose and will slip, which rounds the bolt head.

 

Typical bolt sizes for mower blade bolts are Imperial 1/2", 5/8", 3/4" and Metric sizes 13mm, 14mm, 15mm, 16mm and 17mm.

 

mower bolt damage

Damage

The bolt on the right has a rounded head, this kind of damage happens when a tool slips on a bolt head, or corrosion deforms it. 

Getting the bolt out presents a challange.

mower engine valves

Imperial or Metric

Some mowers will have metric bolts and using imperial sockets and wrenches on them can cause damage. Easily done.

Tools You'll Need

Impact power tools are designed for this exact job. They cause a hammering action which helps reduce the bolt thread friction and breaks any corrosion loose. So if you have an air or battery impact tool, you going to feel like a super hero when that bolt just walks out.

 

Basic tools needed assuming you don't have an impact tool: wire brush, wd40, ratchet & sockets, selection of wrenches.

 

Other tools you'll need if things don't go exactly to plan: breaker bar, hammer & chisel, butane torch, and if everything goes to crap, a Mig welder. 

 

In my workshop, I use an air impact tool, if you haven't got one or can't borrow I have other solutions for you.

 

But the tool I am least likely to be without is an impact tool, it just makes life really easy and saves so much time. The coolest thing about the latest generation impact tools is their mobility, cordless now pack the power of an air tool. Great for around the home and for flat wheel emergency, use it to run the jack up and take the nuts off.

 

Although I still use air in the workshop, I bought a 20v Ingersoll Rand cordless (link to Amazon) for mobile repairs, I know they ain't cheap but you won't ever need to buy another.

 

If you do buy an impact tool, you'll need to buy impact sockets too. Sure you can use regular sockets, but you run the risk of them shattering.

 

mower engine tools

Tool Up

Most stuck bolts won't need all these tools, but some do.

Removing The Bolt

Removing a stuck bolt, involves trying different solutions until you ring the bell. In the first attempts we'll try the simple stuff and if that doesn't move it, I have lots more ideas. 

 

Before we start any work on our mower we need to make it safe. Pull the plug wire off and set it away from the plug. Turn your gas off if you have a gas tap, if you don't know where your gas tap is check out "Gas tap location".

 

WD40 is my favourite tool, it solves lots of problems, I also like a product called nut buster, it's formulated for dissolving rust.

 

Try spraying the bolt liberally above and below the blade, and allow it time to work into the threads.

 

Mower plug wire Mower gas tap Mower gas tap

Disable Mower

For safety, lets remove the plug wire and turn off the gas.

Turn the mower over with the carburettor side facing up, stops gas leaking on the floor.

mower blade bolt clean

Wire Brush

Remove any rust. 

mower blade stuck

Wd40

Spray front and rear of the bolt and give it some time to soak in.

Impact tool Mower on its side

Impact Tool

By far the preferred way to remove a bolt.

An Impact gun hammers the bolt as well as twisting it, this loosens the corrosion between the threads.

An impact tool will remove the bolt in seconds and you won't need to lock the blade.

But if the bolt head is rounded, the impact tool is no use. You'll need a different solution.

mower blade bolt remove

Lock Blade

If you are not using an impact tool we'll need to use a piece of timber to lock the blade against the body. 

Longer timber is better than shorter. Cut a length to suits.

mower blade stuck mower blade stuck mower blade stuck

Good Fit

Select a socket (12 point preferably) and check the fit. 

Turn the Ratchet left to loosen.

Using a breaker bar, or if you don't have improvise with your ratchet and some pipe. 

Pushing down on the pipe will give you leverage, and this will give you the power you need to break it loose.

Just be sure the socket is a good fit, and it stays on the bolt head when your applying force.

Mower blade removal Mower flywheel Mower flywheel

Wrench Leverage

Turn the Wrench left to loosen.

If you don't have a ratchet and breaker bar, try 2 interlocked wrench's for extra leverage, or use a hammer to shock the bolt.

If it still won't budge, try tightening it slightly, this often helps, odd I know!

mower blade bolt remove

Striking

Try striking two hammers, while one is placed against the bolt head, this can help break loose any corrosion on the threads.

If the head of the bolt is rounded, move on to next solution.

Mower blade bolt stuck Mower blade bolt stuck Mower blade bolt stuck

Rounded Bolt

If your bolt head is rounded, try a vice grips.

Get it as tight as you can, and try hitting it to the left sharply with a hammer.

Not all vice grips are the same, for this application you'll need a flat jawed set. (seen in the bottom of the last pic)

Check out this post on Vice-grips tools.

Mower blade bolt removal Mower blade bolt stuck Mower blade bolt stuck

Chisel

This method is pretty effective, but you'll need a new bolt, sharp metal working chisel and a heavy hammer.

With the chisel and hammer, take a side ways and downward aim at the bolt, we'r attempting to loosen it by turning it left.

This will require good aim, so now's a good time for those gloves.

Mower bolt removal Mower on its side

Heat

Ordinarily I'll tell you to get some heat on the bolt, the reason I haven't introduced it earlier is because it comes with the risk of damaging the crankshaft nylon seal, which would cause the engine to leak oil.

The risk of this is fairly small, once you direct the flame and only use a small amount of heat.

We'r not going to redden the bolt, just going to heat it up. Maybe 2 minutes with a butane torch directed at the bolt.

You can now try heat with any combination of the above methods. Heat is very successful at helping move stuck bolts.

Mower blade bolt repair Mower flywheel Mower blade bolt types Mower blade bolt types

Welding

This method will obviously require a welder, when I get a really stubborn bolt with a rounded head, I take a new bolt and weld it to it.

This gives me a not so pretty but a clean bolt head to work with.

This solution has never failed me yet.

You'll need to replace the bolt. Blade bolts have a fine thread, they are a specialised bolt so getting one in the hardware store isn't advisable.

Finally, you'll have to move your timber to lock the blade in the other direction and torque your new bolt to spec. 

Check out this post to see why it's important to torque your blade bolt.

Related Questions

Spindle turns when removing the blades? The easiest way to prevent the blade from turning while loosening the blade bolt, is to use a large block of wood to lock the blade against the mowing deck.

Lawn mower blade bolt direction? Turn the mower on its side, carburettor side up, turn the blade bolt to the left (anticlockwise) to loosen.

Auto Technician and Writer at | Website

John Cunningham is an Automotive Technician and writer on Lawnmowerfixed.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write "How to" articles that help fellow gear-heads with all aspects of mechanical repairs, from lawn mowers to classic cars.