Spark plugs for chainsaws: parameters, selection, condition assessment

Gap and other spark plug parameters

The main parameters that the buyer needs to know:

the diameter of the thread that is screwed into the cylinder;
the length of this thread (colloquially a skirt or shirt);
the gap between the central current-carrying core and the side electrode (ground), between which a spark is formed.

The exact clearance for each chainsaw model is indicated in the Operating Instructions. For different models it varies within the approximate range of 0.45 - 0.55 mm.

There are other options as well. For example, thread pitch. But it is standardized for all candles of this type (M10x1) and they do not think about it when purchasing.

There are spark plug voltage parameters. They are huge, from 10 to 20 thousand volts and above. Manufacturers take them into account when calculating insulators, etc. The user does not need to know the exact voltage.

It is important to remember that if you touch the spark plug contact or spark plug electrode while jerking the starter, you can receive a very noticeable electric shock. It cannot kill, because at high voltage the ignition current has a small force, which is measured in microamps. However, it hits quite noticeably.

Features of adjustment on different models of trimmers

Operating principle

It is necessary to adjust the ignition system so that the fuel ignites in the combustion chamber at the right time.

If the flywheel is shifted on the shaft relative to its original position, the fuel ignites faster than the piston overcomes top dead center. As a result, the piston moves backward and the crankshaft rotates in the opposite direction. Early fuel combustion can be determined by a broken starter cord, broken starter assembly, or other damage.

Sometimes the ignition is late. The piston compresses the unignited fuel and then goes down, and only then a spark is formed. As a result, the engine either does not work, or its power decreases, and the speed increases much more slowly.

Usually the flywheel with magnets is installed in an ideal position, precisely coordinated with the action of the piston, and is carefully fixed to avoid displacement. This allows us to state that incorrect installation of the part is impossible. But if the flywheel displacement is a confirmed fact, then it is a failure or an accident.

Setting up the ignition system is simple and identical on different models of trimmers, be it Stihl FS55, Alco BC 4125 or another lawn mower. First you need to remove the casing from the engine, after unscrewing the fasteners that secure it. This disassembly stage may differ on different models of brush cutters (described below). Next, you need to partially unscrew the fasteners securing the magneto with a screwdriver and turn the flywheel so that the magnets are at the top.

To make the optimal gap between the coil and the magneto, you must use a special template. It is not advisable to buy it for one-time use, so as an alternative, you can use a business card or a small pocket calendar, as well as an A4 sheet of paper folded in four.

The coil will then be attracted to the flywheel by the magnetic field. While holding the magneto in this position, you need to tighten the fasteners that secure it, and then pull out the business card. After this, you need to rotate the flywheel several times to make sure that it does not touch the coil at all. The process is over - the ignition on the brush cutter is set. The process of adjusting the ignition trim system can be studied in more detail on the Internet, where many videos on this topic are available.

Candle manufacturers: review of the best

A spark plug is not a complex high-tech product, so anyone can set up their production in a “garage environment.” This is the main trouble for the consumer, because... Despite its simplicity, it is impossible to make a high-quality product in artisanal conditions of small production. Therefore, the best spark plugs are made by large specialized companies that value their reputation. The most famous of them is Brisk.

In addition, well-known chainsaw manufacturers themselves produce spark plugs.

The following manufacturers produce high-quality spark plugs:

Husqvarna;
Champion;
Stihl;
Patriot.

These are the most famous brands, but the list is incomplete; many chainsaw manufacturers produce spark plugs themselves.

In addition to these brands, “nameless” candles from unknown manufacturers are widespread on the market. They have only digital markings and are much cheaper than branded ones. According to user reviews, they are of unstable quality. If you're lucky, they might even last long enough. Sometimes not for long. It also happens that they are sold initially defective.

Therefore, when the question arises of what to choose: a cheap option or an expensive one, for example Husqvarna or Champion (they are approximately equal in price), it is better to opt for quality.

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Spark plugs are designed to create a spark and ignite the fuel-air mixture in the engine chamber. They differ in diameter, thread pitch and length, and also have different heat ratings.

What to consider when choosing

Recommendations for use

Do not forget that the condition of the spark plug determines how much power the engine will operate with, so its contacts must be kept clean. It is recommended to change spark plugs every 100 hours of using the chainsaw.

Failure to replace the spark plug in a timely manner can lead to a decrease in the power of the equipment.

Source

What is the resource of candles?

Spark plugs are consumables, that is, they obviously have a shorter service life than a chainsaw. Technologically, it is generally accepted that the service life of a spark plug in chainsaws is 100 operating hours. After this period it is recommended to change it. In practice, this period can be significantly higher or lower. Above under the following conditions:

high-quality gasoline and oil are used during operation;
there was no critical overheating of the engine and overheating of the spark plug;
the gap is set correctly, the electric arc (spark) is normal;
preventive measures have been taken: the contact between the central and side electrodes has been cleaned with a “null”, and the contamination inside the spark plug has been removed.

On the contrary, low-quality fuel, overheating, and contamination reduce the service life of the spark plug. An incorrect gap leads to the fact that an arc that is too long or short quickly burns out the electrodes (electric welding effect).

Features of adjustment on different models of trimmers

If the owner of a lawn mower wants to adjust the operation of the ignition system on his own, he should understand the principle of operation of this unit. In an internal combustion engine, it consists of a flywheel and a magneto (coil). In turn, the flywheel includes an impeller that performs the function of cooling the motor and a number of permanent magnets.

Operating principle

When the flywheel rotates, an electric current is generated in the magneto, creating a spark at the spark plug as the magnets pass under the coil.

Before you start adjusting the trimmer ignition, you need to cut off other possible causes of failure and make sure that the problem really lies in this unit. To do this, you need to carry out a number of actions in the following sequence:

inspect the ignition coil housing for damage and defects;
make sure that all nodes and elements that conduct current are free of contamination;
check the integrity and insulation of wiring, contacts, fastening strength, the presence of rust at the joints;
inspect the spark plug cap, as it regularly comes off the high-voltage wire, and they try to restore it manually, and any unreliable connection reduces the power of the spark plug's electric arc;
check the spark plug, since the quality of modern gasoline very quickly damages this part, but there is another possible problem - the spark plug is wet;
Make sure the circuit breaker is working.

Having eliminated all possible malfunctions, you can proceed to adjusting the ignition of the coil.

How to assess the condition of a candle visually

The first sign of a spark plug failure can be detected immediately, without even unscrewing it from the cylinder - a dark band on a white insulator immediately above the iron hex key. This means that the spark plug has lost its seal and combustion products are making their way to the surface. Such a spark plug must be replaced immediately and without options.

Soot rating

It is generally accepted that during normal operation of the entire internal combustion engine and the spark plug there should be a coffee-chocolate colored soot on it. However, this is not always the case. Carbon deposits of this color appear only at high temperatures and after a certain time of continuous operation.

For example, if you cut thick logs at high speeds for about an hour, then the spark plug may have carbon deposits of exactly this color. Conversely, the chainsaw will start quite normally and run for a while at low speeds.

If the saw stalls for some reason, you can unscrew the spark plug and see that it is a little damp from unburned fuel and dark. However, this in no way indicates that the spark plug has failed.

Spark plug depressurization

In addition to igniting the fuel, the spark plug performs another passive function - it ensures the tightness of the combustion chamber, without which working compression and generally normal engine operation are impossible. Depressurization is indicated by the appearance of a dark band on the insulator, as discussed above.

Depressurization occurs exclusively during mechanical destruction. That is, the spark plug insulator could crack or even fall apart. The prerequisite for this can be both manufacturing defects and extreme operation with severe overheating and sudden cooling. For example, when working in severe frost, the candle first heats up. The engine is turned off, the spark plug cools down sharply. If the cycle is repeated, the insulator may fail.

The same can happen if water gets in or gets hit.

Carbon deposits between electrodes

Soot is formed for the following reasons:

non-combustible impurities in low-quality gasoline;
undesirable components in low-quality (fake) oil;
dust entering through a poor-quality air filter;
low combustion temperature during long-term operation of a cold engine at idle speed or in cold weather;
problems with exhaust gases.

In a word, poor spark plug performance cannot be the cause of soot. On the contrary, carbon deposits can cause problems in the operation of the candle. If it forms between the electrodes where a spark occurs, it can act as an insulating pad and the spark will disappear. That is why it is recommended to carefully clean the contact in this place with sandpaper - zero sandpaper after 50-70 operating hours or when carbon deposits appear.

Another weak point of the spark plugs is the internal gap around the circumference between the insulator and the iron body that carries the “minus”. If it becomes clogged with conductive dirt or carbon deposits, then a positive and negative short circuit may occur not between the electrodes, but inside the spark plug body.

The formation of carbon deposits between the electrodes of the spark plug and the connection between the undesirable result and the quality of the fuel mixture is discussed in the video:

Broken central electrode

Among normal candles, such a defect is extremely rare, that is, almost never. It means that the candle simply fell apart, and it was made unknown where and how.

The central electrode is a solid copper rod filled with insulator ceramics. When operating a chainsaw, there are no loads or forces that can somehow stretch or put pressure on this rod. That is why you need to try hard to make the spark plug so that its central electrode breaks.

We recommend reading an interesting article about what to do when you fill a spark plug on a chainsaw and what to do.

Check the ignition coil on a chainsaw

If preliminary actions did not help in identifying the cause of the chainsaw malfunction, then it is necessary to check the ignition coil of the saw. Diagnostics is performed in several stages:

Measure the coil resistance using a multimeter. To do this, you should know the optimal parameters, which are indicated in the operating instructions. However, due to the use of semiconductor elements in the system, if you try to “ring” the coil, the result will be an “Open Circuit” reading. This is fine. A sign of a malfunction is a positive test result. That is, if it was possible to determine the resistance of the coil using a special tool, then it is definitely faulty.
Check for spark with a special device. This device should be installed in the open circuit located between the spark plug and the high-voltage terminal of the saw's ignition coil. The indicators will be visible on the display. This verification method is more often used in service centers, since the device required for this is expensive, and the costs will not be comparable to the benefits provided.
Testing the coil using a spark plug, i.e. perform a homemade ignition. To do this, you need to unscrew it, and then attach the body to the cylinder. Now you need to pull the starter and watch for a spark. But this method only gives an approximate result, since the flywheel spins faster due to the unnatural position of the spark plug.

If none of these methods work, or if you need to check in the field, you can proceed as follows:

Remove the cap from the candle, insert a nail without a head into the core at a distance of 6-7 mm from the cylinder. This must be done as carefully as possible so as not to damage the part.
Perform the steps required to wind the tool. Now you need to look at the presence of a spark and its color. If there is no malfunction, the spark will be strong and the color will be bright blue.

This method can be used as a last resort and only if there are no electronic components, but it is important to follow the rules:

Do not completely unscrew the spark plug, as this may cause the flywheel to rotate faster, which is not the correct engine operating mode;
it must be located at a distance that corresponds to the compression model and dielectric properties of the fuel mixture, so this parameter can be found in the instructions (the value of 6-7 mm is average).