How to Unscrew a Lawn Mower Knife Bolt

The reasons why the bolt may not really loosen are mass. In one case, it is physically damaged (for example, there was a blow), in the other case it is “sticking” from high temperatures (found in the hot parts of a car — a silencer, a collector, a catalyst), and the last is oxidation (such problems occur in parts, which are in contact with water – calipers, silent blocks). Yes, and it happens that the wheel is difficult to unscrew because the “rubber” has not changed for a very long time, say the car was parked in the winter and there is rust that stops the removal process. In general, you need to fight this, there are many ways, ranging from special tools to fairly radical methods. Today we’ll talk in detail about this …

How to Unscrew a Lawn Mower Knife Bolt


  • WD-40 and other penetrating agents
  • Acids
  • Heat
  • Electric heating
  • Physical methods
  • Angle grinder or cut

Personally, in my practice, I met almost every of the listed problems, but the most difficult thing is to unscrew the bolts on the muffler or manifold, because they really stick to high temperatures! By the way, something similar can happen with calipers, because they warm up quite a lot during braking, and then cool down sharply (drove into a puddle). Methods can conditionally be divided into chemical and physical.

WD-40 and other penetrating agents

Actually, the thing is very effective, I advise everyone. Especially if your bolts or nuts are not in temperature loads, and water has got into the thread. This is a very good penetrating substance, it is enough to treat the area and wait half an hour. A bolt or nut yields in 80% of cases.

The disadvantages of this method can be called the price of the final drug, it is quite large. Although now there are a lot of different analogues, but they do not completely repeat the final formula. By the way, you can do enough good analogue Do-it-yourself wd-40, according to my recipe. Watch a short video, useful.


It is also an effective method, however, it is not so safe. For example, if a bolt or nut is next to rubber products, it is best not to use it, because acid can destroy soft materials.

Sulfuric acid of high concentrations is usually used, if the bolt simply oxidized and did not stick, then it is enough to simply drop it on the thread – the oxides will go away and after a few hours everything will turn off perfectly. If you need to unscrew the “hard case”, then a plasticine rim is made around the hat and a few drops of acid are added to add a piece of zinc (to create a galvanic couple). After 12 – 24 hours, almost any bolt, even attached to it, can be unscrewed. However, it is not always possible to make such a side out of plasticine.

Personally, I recommend you to be careful with such methods, yet concentrated sulfuric acid is DANGEROUS!


Heating is very effective in difficult areas such as a manifold, silencer or catalyst. There, the bolts really get stuck, from high temperatures. Turning them off with the WD-40 will not work, and using acid under the machine is difficult. Therefore, here it is necessary to act by the method of "wedge-wedge" kicks. That is, if it is stuck from heating, it means you need to unscrew it through it.

If the mount is small, then it can be heated with an ordinary soldering iron, hold for about 10 – 15 minutes. However, if the case is severe this will not help. An open flame burner works great here – special cans are sold. The bolt warms up almost to a red color, the metal expands (the “sticking” effect is weakened), now it needs to be cooled sharply (preferably with a penetrating compound, like WD-40), it turns out like a mini blow, you can safely unscrew it.

Electric heating

Open fire is certainly good, but here again, there is a chance of burning something! Therefore, it is better to apply electric heating, here we are not talking about a “soldering iron”, rather, here is the principle of the welding machine, but with a low voltage.

A microwave transformer is taken, a thick copper cable is wound onto the secondary winding – this gives us a voltage of 1.5 Volts, but the current strength just rolls over. Two probes are attached to the ends of this wire, preferably from thick sheets of copper, and are ground. These two probes must be installed at the beginning and end of the bolt (or nut and bolt). Thus, a strong warm-up will go, then everything as if with an open source of fire, cool with a penetrating agent and unscrew. We are watching a useful video of such a method.

Physical methods

Actually there are only two of them, but be careful, you can break the line and make it worse, so:

  • Tapping – we take an ordinary hammer and just tapping a nut or bolt (not hard so as not to wrinkle it), often this is enough, oxides, rust or even “sticking” departs and the connection can give in. If this does not happen, try to concentrate the impact, take a “impact screwdriver” and direct the force to the nut or bolt head. DON’T NEED TO PUNCH THREADS, IF YOU REMEMBER IT WILL BE EVEN WORSE, then just cut it off.
  • Leverage or shoulder. Often the key cannot be unscrewed; there is simply not enough lever force. It is enough to lengthen the handle, take a longer “knob” or put a metal pipe on the key, the connection may loosen. However, be careful, you can break the line!

Angle grinder or cut

Perhaps the latest if nothing helps, and even if the edges are torn, then here only – "cut"! Usually this happens "angle grinder", you can hacksaw for metal, if the angle grinder does not crawl (or dangerous). There is actually nothing to comment on, we cut off – we remove the remains – we put a new bolt (nut).

I end here, I want to note – that in 80% of cases, the WD-40 (or the analogue that I showed you) helps. In other cases (catalyst, collector, catalyst), heating helps. Verified – 100%!

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Those who have land are very familiar with what weed control is.

Especially when it often rains and the grass grows by the day and not by the day. Earlier, and sometimes now, this issue was solved with the help of the good old braid.

But technology does not stand still and now assistants such as electric and gasoline lawn mowers are helping in this matter.

A gas mower has several significant advantages over electric, such as mobility and the absence of the danger of electric shock. But there are many shortcomings, for example: high price, a lot of noise, expensive fuel and significant weight.

Fig. 1. The repaired lawn mower

Electric mowers are cheaper, lighter, run on low-cost energy, and are not difficult to maintain and repair. These advantages become the main reason for their great popularity among buyers of this type of equipment.

But despite the pretty good quality, improper operation and heavy load, they can damage the device. In such cases, you should not immediately bring the device to the repair shop, but try to find and eliminate the cause of the breakdown yourself. Moreover, as mentioned above, electric lawn mowers do not have as many components and parts as gasoline ones.

The main thing is to have some tools and self-confidence. In this article, I will just show you how to repair the lawn mower with your own hands.

Fig. 2. AL-KO lawn mower

An AL-KO lawn mower was taken as an example, which had serious problems in operation, namely: stopping the engine without load and severely overheating it. The motor stops, hoots and starts it again, only pressing the “START” button again helps. You have to restart the button almost every 30 seconds, and with further work more often.

Of course, you can work this way, but it is very annoying and gives the feeling that there is a problem somewhere.
So I wanted to figure out where?

After operating the mower for an hour, the engine temperature was measured. It was impossible to touch him with a finger. He radiated heat directly. If you do not continue to pay attention and continue to work on such a mower, the electric motor will inevitably fail.

The lid is held on six screws with a cap for a Phillips screwdriver.

We unscrew these screws and remove the cover – upward movement.

Fig. 4. Removing the cover

Having removed it, you can see the impeller, the capacitor, two connectors and the motor itself.

At first glance, no particular problems are visible. The temperature of the motor winding has darkened slightly, but so far this is not critical.

Fig. 5. Impeller, capacitor, two connectors and the motor itself

To examine the capacitor more thoroughly, it is necessary to unscrew the mount and pull it out.

Fig. 6. We take out the capacitor

The capacitor did not show any external damage.

Fig. 6.1. Lawnmower Capacitor

Next, try to spin the impeller. It is mounted on the rotor axis and rotates quite tight.

Fig. 7. Turn the impeller

And the reason for such a heavy rotation is the mechanical brake, which, for safety, stops the rotation of the engine when the power is turned off.

It looks like a sleeve that moves freely from top to bottom, along the axis of the rotor.

When no voltage has been applied to the engine, this bushing is pressed with the upper part against the cover, on which two rubber bands are glued. Thus, the knife is braked, mounted on the rotor shaft.

When power is applied, the brake sleeve is pulled toward the center of the rotor under the influence of a magnetic field and provides free travel.

Fig. 8. Mechanical brake

Upon careful inspection of this bushing with the brake, it was noticed that at the moment the engine was turned on, the brake is pulled in and gives the shaft free rotation, but after 2-3 seconds it is released again and the motor starts to brake. This should not be. Hence the knife stops during operation and the engine overheats.

To find out what is the reason for such work, it is necessary to remove and disassemble the engine.

To do this, disconnect the connectors and put the device on its side to get to the clamping screws. Access to them closes the knife with fasteners.

To remove it, first you need to unscrew the bolt of the knife (see figure below).

Fig. 9. We unscrew a bolt of fastening of a knife

This is done with the key to nineteen.

Direction of rotation, as with a regular bolt, not with a left-hand thread. That is, it should be unscrewed counterclockwise, and twisted clockwise.

The head of the bolt is plastic, therefore, using a key, it must be inserted well so as not to “lick” the edges.

After removing the bolt, the knife and its plastic disc are removed.

Fig. 10. Remove the knife. Figure 11

Below it is a height sleeve. With it, you can slightly lower the knife.

Adjustment is made by washers placed under the sleeve (see the figures below).

Fig. 12 Fig. 13 Fig. 14

We remove everything, only the motor shaft and the hexagonal screws for its fastening remain.

The key for these bolts has a 6 mm spacing between faces. Unscrew them counterclockwise. When removing the last screw, hold the engine with one hand.

Fig. 15. The motor shaft. Turn off the bolts

Next, put the mower on the wheels, and clutching the engine with your hands – we raise it.

Fig. 16. Fig. 16. Lawnmower engine 17. Lawn mower engine

To disassemble the motor, you must release the tightening studs. Unscrew them all.

Fig. 18. Disassemble the lawn mower motor

Remove the impeller with two screwdrivers.

Fig. 19. Removed the impeller

We proceed to remove the back cover. This will help a wooden block and a hammer.

But first, you need to use something sharp to mark the position of the covers in relation to the engine housing.

Fig. 20. Marking the position of the covers

We put the engine on its side and hit it with a hammer, through a wooden gasket, on the rear shaft.

Fig. 21. Hit the rear shaft

The motor at this moment should be held by another person.

We hit until the axis until the end comes out of the bearing.

Fig. 22 Fig. 23 Fig. 24

You can also raise the engine vertically and hit the shaft on a wooden plank. This method can also remove the shaft from the bearing.

If the shaft is out, remove the cover, the brake sleeve and two brackets on it with a screwdriver.

Fig. 25. Remove 2 staples with a screwdriver Fig. 26. Brake bushing

Now that the brake elements are removed, we install the back cover back. We look for previously set tags, and combines them.

Fig. 27. Brake elements removed Fig. 28. Install the back cover back

Pass the connector with wires into the cutout of the cover.

Next, we put the cover with the bearing on the shaft and tapping on it from all sides, we achieve complete installation.
The lid should not be hit hard so that brittle aluminum does not crack. Therefore, blows must be applied through wood or rubber.

Fig. 29. Put on the cover with the bearing

When the cover with the bearing tightly “sat down”, we tighten the tightening studs. They should be clamped gradually diagonally. At the same time, we achieve maximum ease of rotation of the motor shaft.

Fig. 30. We twist the tightening studs

Next, we put the impeller on the rotor. With its help, the engine is cooled during operation.

Fig. 31. We put the impeller on the rotor

First we put the impeller in our hands, and then, with light tapping with a hammer in the center. Too deep to “plant” the part also should not be, otherwise it will cling to the engine cover.

Now lower the engine to the seat.

Fig. 32. Lower the engine to the seat

We connect the motor and capacitor connectors. It is very important not to confuse which plug to where. Otherwise, the engine will not work properly. Therefore, when disassembling, everything must be signed and photographed.

Fig. 33. Connect the plugs

Next, you need to fix the motor. To do this, put the mower on its side, and holding the engine by the impeller, combine the holes for the bolts.

Having tightened all four bolts, squeeze them with a hex wrench. This should also be done diagonally.

Fig. 34. We tighten the bolts

After that, we plant the next part on the shaft.

Fig. 35. We install the part

We install the base for the knife and the knife itself on it.

The knife must be installed with its bends up. They are needed in order to push the cut grass back into the container.

Fig. 36. Set the knife back

The whole structure is clamped with a plastic head bolt. We try to rotate the knife by hand. He must move without rubbing and creaking.

Fig. 37. Clamp the bolt

Now we put the machine on the wheels, and install the protective cover. We fix it with screws.

Fig. 38. Install the protective cover

We turn on the engine and listen to its work. In this case, there should be no extraneous sounds, but only a slight rustling of the knife.

Finally, check the mower on the grass.

Fig. 39. The mower is working!

As you can see, the car copes with its task without blackouts and braking. Now you can not be afraid that the engine will overheat, and get out of standing.