The design of a trimmer

Although petrol trimmers may differ in small details, they still have a similar overall design. Under the plastic body is the heart of the trimmer — the engine (1). On the left side, the device is equipped with a fuel tank (2) of a certain volume, into which a mixture of oil and petrol is poured in the proportions specified by the manufacturer. Almost all models have a rubber or foam thigh guard (3) located on the shaft in close proximity to the engine, which reduces vibration transmitted to the user's thigh. Below are rubberized handles, one of which holds the control system (4) in the form of a throttle valve and a start lock button.

The aluminium or steel shaft (5) is connected to a gear (7), which is responsible for rotating the nozzle (8). To protect the user from grass flying in all directions, the trimmer is designed with a plastic or metal guard (6).

Design of a petrol trimmer.

Features you should pay attention to when choosing

Before purchasing, pay attention to the following indicators:

  • Power. The power of the string trimmer largely affects its performance. For regular mowing of the lawn, models from 800 to 1500 watts are suitable. For mowing tall and thick grass it is worth looking at models from 1500 to 2500 watts. And if you need to cut tree shoots, you should buy a device with a power of over 2500 watts. Professional models with a power of 3000 – 4000 W will be attractive to utility companies and private companies engaged in clearing the city of overgrowth.
  • Engine's type. Most string trimmers are equipped with two-stroke engines, the power of which is enough for almost all tasks. However, their disadvantage is a rather high level of noise, so when using them, it is extremely important to use earmuffs to avoid hearing damage. Also, two-stroke engines are fueled with a mixture of oil and petrol, by mixing up the proportions of which, you can harm the device. Some models, such as the Makita EBH 341U, have a four-stroke engine, which is less noisy than a two-stroke one and consumes less fuel. Also, filling oil and petrol is done in different reservoirs, so you can not overdose it. However, devices equipped with four-stroke engines are heavier than their two-stroke counterparts, and they are more expensive.
4-stroke engine string trimmers
  • Shaft design. Straight shaft models are the most common and powerful among petrol trimmers, featuring an aluminium or steel shaft housing a metal drive that transmits rotational impulses to the gear, rotating the nozzle. Despite their slightly heavier weight, they are suitable for most tasks. On the other hand, curved shaft models use a steel rope to rotate the nozzle, resulting in less torque transmission and smaller engines (0.8 to 1.1 hp). Curved shaft trimmers are lighter (up to 5 kg) and more convenient for treating flowerbeds, cutting figured lawns, and reaching grass under benches. They are ideal for cutting low, thin grass and regular lawn maintenance. Additionally, collapsible models, both with straight and curved shafts, offer compactness when disassembled, facilitating transportation and storage in garages.
Curved and straight shaft type.
  • Cutting width. This indicator determines the distance that the cutting head of the trimmer captures. There is a relationship between the power of the device and the grass cutting width: the more powerful the device, the easier it will be for it to mow a wider area. The optimal cutting width for petrol trimmers is 40 centimeters — suitable for medium and large areas.
Trimmers with line diameter > 2 mm
  • Attachment. As standard, every string trimmer is equipped with a spool with a line wound on it. This attachment is useful for cutting soft grass and mowing the lawn. In principle, it can also cut thick grass, but then it will wear out quickly. For most models, it is better to take a line from 2 to 2.8 mm thick (if the diameter of the hole in the spool allows it). Note that the line material must be able to withstand the high temperature generated by friction so as not to melt and stick to the spool. Therefore, when choosing components, check with the seller whether the line can withstand 200 degrees. If you have to trim overgrowth and thick grass, it is better to use a paddle blade or disc. The second one usually has a smaller cutting width, but is capable of cutting small trees well.

A variety of attachments for string trimmer.

  • Belt. Considering that most models weigh more than 5 kg, it is worth buying one with a double-shoulder belt, especially if you plan to mow the grass for several hours. Some manufacturers, such as STIHL, make comfortable double-shoulder belts with plastic thigh protection against vibration. Please note that most devices provide the ability to attach a belt from a third-party manufacturer, so a suitable option can always be purchased separately.

Double-shoulder belt with thigh protection.

  • Shield. It is extremely dangerous to work without this part, so it must always be in good condition on the string trimmer. There are plastic and metal shields. If it is necessary to mow in an area where there are many stones and other hard objects that can fly from the metal disc, then the plastic shield can simply break - here you need a metal shield. It does not always come in a set, but it can be purchased at any time. When buying, pay attention to the size of the discs.

Shield.

  • Handle type. Trimmers with a loop handle are usually relatively lightweight devices up to 5.5 kg (heavy models are less common). This type of handle has only one advantage over a bike handle — portability, which makes the device easier to transport. Otherwise, the bike handle is superior to the loop one in terms of mowing comfort: it is easier to move the trimmer through the grass and makes the hands less tired.

Bike and loop handles.

  • Weight. If it is planned to mow the grass frequently for a long time, it is best to take models with a weight of 3 to 6 kg. The purchase of heavy powerful devices weighing up to 12 kg is only due to the need for constant mowing of thick tree shoots, so it will be interesting for utility companies.

Important: if almost any engine oil is suitable for the mower gear, then for the engine you should use only the oil specified by the manufacturer, which is mixed in a certain proportion with petrol (for 2-stroke engines). If you add more oil, the engine will smoke, and if less, then rapid wear of the friction units will occur — regularly ensure that the proportions are strictly observed.

Engine oil for petrol tools

Conclusions

To keep the lawn in good condition and to cut low, thin grass, you should take a light string trimmer with a curved shaft with a power of up to 1000 watts. If it is necessary to mow the high thick grass, it is better to look at models 1500 – 2500 W, and to buy additionally a paddle blade or disc for trimming the growth. The purchase of professional powerful devices is justified only for utility companies or specialized private companies.