The Forensic expert kollegium conducts expertise of petrol tools with two-stroke and four-stroke gasoline engines and engines of the “4-mix-Motor” model, including:
- chainsaws;
- gas trimmers and brush cutters (petrol mowers, lawn mowers);
- stone cutters;
- lawn mowers;
- motor cultivators and motor blocks;
- portable electric current generators;
- vibrating plates.
Using light two-stroke internal combustion engines has become widespread in various fields of activity, especially in the field of housing, communal services and in the personal households of citizens as part of chainsaws, trimmers, walk-behind tractors, scooters, outboard motors and other mechanisms. The simplicity of their design and maintenance in operation often creates an apparent simplicity in their use. However, most product manuals recommend the user to have some knowledge of how to operate and handle the device. For example: "Everyone working with the device for the first time should be instructed by the seller or other specialist on how to properly handle the device - or take a special training course".
From studying the design and arrangement of two-stroke engines, two very important features should be distinguished that affect the rules for handling the device.
First, two-stroke internal combustion engines do not have a separate lubrication system. Lubrication of rubbing parts is carried out through the part of the oil that is contained in the gasoline-oil mixture. To prepare a working gasoline-oil mixture, the oil is subjected to preliminary mixing of gasoline and oil in a canister before refueling, observing the proportions established by the manufacturer (pre-mixing method / «Premix» method).
Secondly, two-stroke internal combustion engines have air cooling as the main cooling, and as additional cooling, the removal of part of the heat is assigned to the lubrication system, i.e. on that part of the oil that is contained in the gasoline-oil mixture.
Based on the listed design features of two-stroke internal combustion engines, some features of their use also follow:
- Strict observance of the manufacturer's requirements for the established proportions of gasoline and oil used to prepare a working gasoline-oil mixture by pre-mixing gasoline and oil in a canister before refueling. Manufacturers, which, as a rule, are occupying the leading positions in the market for this type of product, give the proportions of gasoline and oil for preparing a working gasoline-oil mixture in the instruction manual using only branded (original) motor oils. At the same time, a number of manufacturers set the proportions of gasoline and oil for the preparation of a working gasoline-oil mixture using both branded (original) motor oils and oils from other brands, as a rule, increasing the oil concentration from 1:50 to 1:33 and even up to 1:25.
- In any case, the concentration of oil in gasoline in the composition of the working gasoline-oil mixture is a constant value, in any case, at least for a given gas station, and the operation of a gasoline tool is characterized by a constant change in the operating mode both in terms of engine load, engine speed and operating temperature of the device. And only the user of the tool has the responsibility, as well as knowledge, skill and experience of maintaining the tool in each specific moment of time and in each specific mode of operation (engine load, engine speed, operating temperature) with the concentration of oil in gasoline as part of the working gasoline-oil mixture, which is available in this particular gas station and which can provide adequate lubrication and cooling of rubbing surfaces, as well as trouble-free using (application) of a chainsaw.
From the expert practice of the Forensic expert kollegium, it is known that, until recently, the most common cause of a malfunction of a gasoline tool was its operation with an improper gasoline-oil mixture with a low oil concentration. However, recently failures of a gasoline tool due to the use of an improper gasoline-oil mixture are becoming less and less common.
The most common cause of a malfunction of a gasoline tool currently is the poor-quality manufacturing of components and parts of a gasoline tool and using low-quality components and wear parts during repair and (or) maintenance in a repair shop.
Much less often, as a result of an expertise, the causes of a malfunction of a gasoline tool are established, such as:
- operation of a gasoline tool with an unacceptable excessive load;
- operation of a gasoline tool in unacceptable conditions;
- shock or thermal impact on the gasoline tool.
Most likely this is due to the fact that the failure of a gasoline tool due to unacceptable (excessive) load, shock or thermal effects are the most obvious and usually there is no litigation about the reasons for the failure.
Users should be informed that, unfortunately, some gasoline tool service centers still, due to insufficient depth of research, in a significant number of cases are naming “using an improper petrol-oil mixture” as the main reason for the failure of a gasoline tool, misleading users (consumers).
Experts of the Forensic expert kollegium, on the basis of expert practice, confirm that there are other (at least two more) causal options for the failure of a gasoline tool, when the external signs of their manifestation are similar to the signs of failure of a gasoline tool due to “using of an improper gasoline-oil mixture”, although in fact they are not.
There are a number of objective signs that are revealed during disassembly of the product and microscopic, physico-chemical, strength study of its parts, allowing to make a categorical conclusion about the presence of manufacturing defects or unacceptable operating conditions.
In most cases, it is enough to set the following questions for resolution of the expertise of a gasoline tool to determine the nature of the damage:
- Is the presented tool in working condition?
- If there are defects in the presented gasoline tool, what are the reasons and nature of their occurrence?
- Are there any signs of violation of the operating conditions on the presented gasoline tool by the consumer?
- Does the presented gasoline tool show signs of using an inappropriate fuel mixture?
- Are there any signs of operation of the presented gasoline tool with unacceptable overloads?
The gasoline tool must be submitted to the Forensic expert kollegium with operational documentation and all nozzles included in its delivery, case materials reflecting the conditions under which the malfunction of the gasoline tool occurred. A feature of the gasoline tool (for cases of checking engine operating modes) expertise is the need to provide the proper fuel mixture in an amount sufficient to fully refuel the tool before expertise as part of an examination of the engine's serviceability.
You can contact the Forensic expert kollegium on the issues of a gasoline tool expertise at: Minsk, Zhukovskaga St., 11A, 4th floor
or by phone: +375 (17) 317 04 71; +375 (17) 317 04 72; +375 (17) 317 04 73; +375 (17) 317 04 74; +375 (17) 317 04 76; +375 (29) 109 60 11; +375 (44) 588 60 11
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