How to turn a grass trimmer into a boat motor

How to make a motor for a boat from a grass trimmer: ways and tips

If desired, you can make a boat motor yourself from any trimmer for grass. However, it is important to consider that the models are available with different components. Some trimmers have a long stand, and it will not be suitable for a boat motor.

Also the problem is to find a quality propeller. It can be positioned in a horizontal or vertical position. In order to understand this issue in more detail, it is necessary to consider specific modifications.

Devices with a double-sided flywheel

Redesigning the grass trimmer into a boat motor with a double-sided flywheel is quite simple. The screw for this should choose a small diameter. Grass trimmer is suitable for manual control and low power. Start the assembly by fixing the stand.

If we talk about a simple model, the starter does not need to be touched. When assembling the deadwood, it is important to pay attention to fixing the connector. The screw is installed on the rack last. The flywheel is mounted behind the starter in order to change the position of the tube. Operation of these motors is very simple. To prevent water from getting on the connector, various covers are used.

Converting a grass trimmer into a boat motor

Methods of making a boat motor from a grass trimmer

There are three ways to build a boat motor from a grass trimmer. They differ in the details used and the principle of self-assembly.


This method stands out for its simplicity and cost-effectiveness.

You will need to prepare for the work:

  • Clamp, which is necessary to fix the device on the transom of the boat;
  • Propeller. you can buy it ready-made in a store. The unit comes standard with a drive unit made of stainless steel, and adapters to be connected to the flexible shaft of the household brushcutter. Some models of propellers are supplied for sale together with clamps, so the buyer will need to clarify the set of parts included in the kit in advance.

As a rule, there is a ready-made drawing of the propeller in the kit. This allows you to save money on finding the necessary schemes for work. It takes approximately 1-1.5 hours to assemble the boat motor.


To assemble the boat engine, the maker will need to prepare an angle reducer, which can be removed from the angle grinder. You also need a propeller for modification. you can cut it out of stainless steel sheet and bend the blades at the right angle.

Despite the relatively small pitch of the resulting propeller, this method of modification makes it possible to achieve the maximum possible revolutions from the engine. The only disadvantage is the need for additional adjustment of the engine, for which you can use pliers.

The method

This method differs from the others by the possibility to make some parts for the boat engine with your own hands. Requires a 2-stroke gasoline engine with a cylinder volume of 25 cm3. Motor power from the grass trimmer must not be less than 0.7 kW, and its weight. no more than 4.5 kg. The unit must be equipped with a bent leg. The engine from the grass trimmer, which meets all these parameters, will allow you to move the boat with a speed of 5 to 8 km / h with minimal fuel consumption. The principles of its manufacture in more detail below.

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What is the attachment for converting a grass trimmer into a boat motor

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Working principle

Motor for the boat from the grass trimmer has a higher speed of rotation of the blades, which allows you to move faster on the river. When the gasoline mower works when mowing lawns, its blades are turned to the other side. When making a motor for a boat, flip the motor blades. Then the engine will work to push the boat. The higher the blades are to the water surface, the faster is rotation speed and the faster is boat speed.

What’s the hose on the exhaust.what kind of material?

This motor is long gone, and the hose is metal, some kind of corrugated

I must have missed it, when I was making one, a 5.4hp grass trimmer for a single seater boat, it was something else. In the test, even the propeller blade came off, it was scary as hell.

Well done, I see you have a hard welded leg bracket, but it needs to tip over, like on the PLM.

The whole motor and transom tipped over, but that motor and the boat are long gone. But the record is still here.)

Original! For beginners song! Let it be loud

How the gearbox sealing was implemented? There’s a hell of a lot of holes for blowing through, the water will flow through all of them into the shaft bearing area

There is a little bit of grease and the gearbox has had a good winter, checked the other day, everything rotates and does not whistle.

The stern tube goes straight to the shaft bearing or something? I understand there is no water ingress in this way. I have a gearbox from a 230 angle grinder and there is a bearing just paired with water will molotuyut (the upper primary shaft)

What’s the hose on the exhaust?What kind of material?

That motor’s long gone, and the hose is metal, it’s some kind of corrugated hose

I must have missed it, I was making a grass trimmer 5.4hp for a one man boat. it was something else. Even the propeller blade flew off at the test, it was scary as hell.

Well done, but I see you have a hard welded leg bracket, but it needs to tip over, like on the PLM.

There was a tipping of the whole motor with the transom, but that motor and the boat are long gone. But the recording is here to stay)

Original! For beginners song! Even though it’s loud

how to seal the gearbox? there are a lot of holes for purging, through all of them water will flow into the bearing area of the shaft

It’s packed with grease and everything, the gearbox has had a good winter, we checked it the other day, it all rotates and doesn’t whistle.

The deadwood tube goes straight to the shaft bearing, what? I take it that’s where the water ingress is eliminated. I have a gearbox from 230 angle grinder and a bearing just paired with water will grind (the upper primary shaft)

A ready to use nozzle kit

Now sell special attachments for converting grass trimmer into a boat motor. Such an attachment includes everything you need to attach to a gasoline mower motor. Control handle and push button switch are mounted to the boom. The throttle handle is made with the ability to switch speeds and has a ratchet that locks the desired position.

The kit includes a fixture for mounting the unit to the boat. The grass trimmer head can be easily assembled, it has a simple design. To reassemble, attach the throttle cable to the motor, and then secure the muffler cable. The nozzle costs about 5 thousand rubles at a specialized store. Roubles.

Ready-made set of nozzles

Now they sell special attachments for modifying the grass trimmer into a boat motor. This attachment includes everything you need to attach it to your gasoline mower motor. A control knob and a switch button are installed on the boom. The throttle grip is made with the ability to shift speeds and has a ratchet that locks into position.

The kit includes a fixture to mount the unit to the boat. Grass trimmer attachment can be assembled easily, it has a simple design. To assemble it is necessary to attach the throttle cable to the engine and then fix the muffler cable. The nozzle is in a specialized store for about 5 thousand rubles. rubles.


Why can’t I keep the standard flexible shaft.

Replace the flexible shaft with a steel pin because of the heavy load on this torque transmission system. Under load, the flexible shaft will not be able to rotate evenly, the boat will move jerkily. In addition, in this mode, the regular grass trimmer shaft does not work long at all.

How a factory propeller from a store is better than a homemade one?

A purchased propeller has a calibrated shape that allows you to achieve maximum efficiency of the entire construction. In addition, boat propellers are often sold complete with the necessary fasteners sleeves. This simplifies the redesign of the grass trimmer into a boat engine, but requires a certain financial investment.

Is it possible to use a propeller of a larger diameter than 100 mm?

Yes, it is possible and it is even possible to achieve higher propulsion speed. However, in this case the construction will have to be retrofitted with a gearbox, because the engine power of the grass trimmer is not enough to rotate a large propeller. A gearbox from a trimmer head may be used. To fix it you will need another pair of clamps. To prolong the service life of the gearbox, it is necessary to ensure the constant presence of lubricant in its housing.

Methods of making a boat engine from a brushcutter

The easiest way to make a motor for a watercraft is to use a brushcutter with a straight leg (rod) and therefore a rigid shaft. In this case all reworking comes to producing a propeller, which you can cut from a strip of stainless steel or duralumin. The workpiece size. 100x30x2 mm. The blades should be given a curved shape, for which you need to bend them by about 10 mm. The edges of the propeller must be sharpened. An example of a simple propeller drawing is shown in the figure below.

Important! Dimensions, quantity of blades and angle of bend are chosen individually, based on the weight and size parameters of the boat and the engine capacity of the grass trimmer.

The propeller that you have made is installed in place of the trimmer head. In this case it is desirable to use a ring attachment, which will not allow the propeller to damage the boat. In more detail the process of grass trimmer revision with their own hands is shown on the

Revision of the gearbox of the angle grinder

To achieve maximum engine speed, the grass trimmer can be equipped with an angle reducer from an angle grinder, which must first be finalized. At the same time you may need oil seals and bearings. The process of finalizing gearbox consists in replacing the short shaft for a longer one, corresponding to the size of the trimmer rod for grass. But you will have to dismantle the gearbox for this.

Important! The shape and connecting dimensions of the new shaft must match the parameters of the assembly removed from the gearbox. This, in turn, will allow to use the existing bearings and pinion in the gearbox.

After you have made the new shaft, assemble the gearbox, having previously protected the bearing with an oil seal that prevents water from penetrating into it. It is also recommended that the existing gear wheels are greased or the housing should be filled with grease. Rubber seal and/or sealant is used for sealing the body.

As a side note! Increasing the revolutions of the trimmer engine through the gearbox, the propeller should be attached to the output shaft of the latter.

Finishing of grass trimmer with a bent bar

If the owner of the boat has a lawnmower, the boom of which is curved, the latter must be dismantled and replaced with a straight tube of the appropriate diameter, made of duralumin. If the diameter of the new tube will be larger than the size of the hole in the engine block, the seating will need to be turned to the correct size. Proceed as follows (see drawing). drawing).

  • First unscrew the standard nut 2, which is located in the cord bobbin. At the same time it is strongly not recommended to throw away the fasteners removed from the boom, as the manufacturers of brushcutters often use their own types of threaded connections that do not correspond to the standard ones.
  • Then unscrew the original nut 4 and remove the stern shaft (pos. 8) and flexible (pos.9) shafts.
  • Then a sliding bearing 6 is cut out (this has a bronze sleeve at the end of the shaft).
  • Then the plastic tread 10 is knocked out of the rod.
  • The previously extracted plain bearing 6 is pressed into a straight pipe 7 of suitable length. It may be necessary to bore out the tube for this.
  • Then the plain bearing 6 is carefully pressed with a hammer on the groove 5. Here it is important not to damage the pressed bronze bushing.
  • Then the plastic protector 10 is cut to suit the position and fitted tightly into the pipe 7.
  • Then the stern shaft is connected to the steel bar, which will replace the flexible shaft 9. This may require the help of a turner.
  • The final step is to attach the propeller 3 to the stern shaft 8 using the nut 2.

The assembled rod is connected to the motor with the help of specially made adapters, the shape and size of which depend on the design features of a particular model of trimmer for grass.

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How to properly use a boat motor from a brushcutter?

Using a grass trimmer as a boat motor, the operator needs to constantly monitor the condition of the engine, and give it time to cool down.

In addition, to extend the life of the boat motor from the grass trimmer will help:

  • Checking all the fixings in the device. before each start of the engine, you need to carefully inspect the locks that hold the elements of the engine from the trimmer for grass;
  • filling up the engine of the grass trimmer only with the petrol and oil that was used to operate the brushcutter;
  • timely cleaning and replacement of the engine air and fuel filter;
  • regular inspection and timely replacement of the fuel pump;
  • inspection and, if necessary, replacement of the spark plug.

To extend the life of the boat engine from the grass trimmer will also help to regularly ventilate its regular cylinder. For this purpose, about once every 2 months you need to unscrew the spark plug, and 4-5 times rarely pull the starter rope. After the procedure, the plug can be screwed back into place and continue operating the engine.

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Boat motor from a trimmer for grass: step-by-step instructions for conversion

Almost every fisherman has a rubber inflatable boat at home. And of course, everyone would like this form of transport to be as fast, convenient and comfortable as possible. If in addition to the inflatable boat you have a lawn mower in the economy, you can construct a homemade boat motor on the basis of the trimmer for grass. Such a device is made quite easily and quickly, and its performance and reliability will be quite enough to move the boat for long distances. Here’s a step by step instruction on how to rebuild a boat motor from a brushcutter.

Using a grass trimmer as a boat motor has a number of significant advantages and benefits.

The benefits of this technical solution:

  • low cost: the grass trimmer is much cheaper than a professional boat motor;
  • small fuel consumption with sufficient performance;
  • reliability and tightness of design, taking into account the individual nuances of use;
  • small dimensions and weight of the tool, which is also very practical and convenient for use on light boats;
  • control of fuel thanks to the transparent walls of the tank;
  • rigid shaft inside the boom.

Motor power should not be less than 0.7 kW. Ready-made conversion attachments (attachment for attaching to the engine, special adjustable handle with muffler button, mounts) can be purchased. After installing them on the grass trimmer, you will only need to connect the throttle cable to the engine and connect the wires to the muffler.

How to make a boat motor with your own hands from a grass trimmer?

To create a boat motor from a lawnmower, a tool with a straight boom is suitable. If the grass trimmer boom is curved. you will have to work on its improvement.

The modification is done according to this algorithm:

  • First remove the original nut (marked with number 2 in the drawing below). Do not throw it away or lose it, as you cannot replace the factory nut.
  • Unscrew the rest of the mounts, take out the flexible shaft and the flexible shaft (figures 8 and 9 in the drawing).
  • Fit a new duralumin rod with a slightly smaller inside diameter. Carefully place the bronze sleeve (see drawing) in it.
  • Cut the tread (part 0) to the required size and insert it into the rod.
  • If the outside diameter of the boom will be too large for the motor hole, turn it.
  • Using the original nut, fasten the screw.
  • The shaft is fastened to the motor by means of adapters. There are no universal drawings for this part, because different models of trimmers have their own design features. You can order this detail in a lathe, or make it yourself from plywood. The construction will be fastened with 4 screws.

If there is no possibility to buy a ready-made set for modification, which was mentioned earlier, the adjustment handle can be taken from a sports bike handle.

You can also make the screw yourself from a piece of duralumin using the drawing below:

The pitch is the distance from the blade to the horizontal surface. Tilt angle can be adjusted with pliers. To do this, preheat the workpiece.

To refuel the motor from the grass trimmer on the boat, use only high-quality fuel and lubricants. Dilute the gasoline with oil in the appropriate proportion. The first 10 kilometers do not expose the engine to high loads. this will be the break-in period. Depending on the engine capacity, a boat with such a motor can reach a speed of 5 to 8 km/h.

Below is a video that demonstrates the work of such a unit:

Advantages of using a grass trimmer

First of all, it is worth considering the main advantages of using a grass trimmer to make a boat motor:

  • the cost of the grass trimmer is much lower than the cost of a complete motor for the boat;
  • very economical fuel consumption;
  • reliability in operation;
  • Low weight, which is very important when using a grass trimmer on rubber boats;
  • built-in translucent fuel tank, through the walls of which you can clearly see the level of gasoline;
  • quite hermetic design;
  • a rigid shaft is installed in the boom;
  • there are ready-made elements for controlling the unit (starter and gas).

All these qualities of the unit put it in the first place, if we take into account other options for remodeling. So, to trimmer for grass (requires power from 0.7 kW) turned into a full-fledged boat motor, it is necessary to buy a special set of attachments or make them with your own hands.

Tuning the outer parts of the Ural

Here the direction of tuning depends on the style in which you want to make a motorcycle. Usually owners choose classic custom variants.

often than not, the look of the Ural is subjected to such changes:

  • replacement of fenders, handles, mirrors, fairings, seats, running boards;
  • Chromium plating the parts to get more shine;
  • changing the shape of the fuel tank and steering wheel;
  • making a new muffler.

Ural. Cafe Racer

One of the easiest and most popular styles of customization. In the process of remodeling the Ural, unnecessary parts are removed, and the old heavyweight ones are replaced with lightweight and stylish.

The tail of the motorcycle is rewelded to create an aerodynamic hump, a new seat is installed. And also the wheels are updated: they should be spoke, with lightweight rims and road rubber.

Read more about how to make a Cafe Racer here:

Ural. bobber

Also quite a popular direction of customizing among owners of the Ural. In this case back part of a frame is changed and back shock absorbers are removed. The tank is replaced by its reduced copy, and a small single seat is also made.

In principle also nothing particularly difficult, the only thing that will have to tinker with alteration of the motorcycle frame. And it is made of strong mild steel, so it is quite difficult to be rewelded.

Read more about building a Bobber with your own hands here:

Ural. chopper

This is the most complex and costly type of tuning Ural with their own hands. Firstly, it is necessary to make completely new frame. Most often for this use ordinary water pipes with thick walls.

You will have to labor with finding and installing a wide rear wheel, not less than 150 mm. The exhaust pipe will also need to be redesigned to look stylish.

Chopper driver should sit valiantly, so the footrests will need to be moved forward, as well as change the location of the motorcycle controls. And, of course, to make a large and wide handlebar.

The last step will have to take care that all parts of the motorcycle will be covered with chrome and dazzling shine.