How To Check The Magneto Trimmer

Trimmer ignition coil malfunctions and repair How to repair the trimmer ignition coil: check the operation, remove and disassemble, replace the breaker and magneto contacts. What coil malfunctions can be, and how to avoid them.

Problem prevention

Often, breakdowns of the ignition coils are associated with a short circuit or breakage of the windings and mechanical damage to the magneto case. This is due to strong shocks, liquid ingress and oxidation, and overheating.. If you avoid such incidents, you do not have to worry about the integrity of the ignition coil.

how to check the magneto trimmer

One of the magneto assemblies that regularly suffer from use are the high voltage wires through which the spark plugs receive current from the ignition module. They have a long service life, but they are damaged by the users themselves by careless handling when replacing candles, inadvertently pulling on the wire itself, and not on the tip. Another problem that can occur with them is moisture ingress and oxidation or damage to the insulation. By carefully pulling out the spark plug and avoiding liquid penetration into the instrument, these problems can be avoided.

So, the repair of the ignition coil is not very difficult and can be carried out by the user independently, but subject to the above procedure for disassembling and replacing the magneto or breaker contacts.

Magneto design and operating concept

The purpose of the ignition coil is the conversion of rotational energy into a high-voltage discharge and the formation of a spark that ignites the fuel mixture. In an internal combustion engine, this part is called a magneto, since in it an alternating current is generated from the rotation of a permanent magnetic rotor or armature.

Magneto structurally consists of two windings: high and low voltage. A capacitor with breaker contacts is connected in parallel to the latter. Whereas the leads of the high voltage winding are connected to the candle and the body. They are both wound on a core, between the poles of which a rotating magnet is installed, magnetized longitudinally.

Method 3

If there is no multimeter, you can check the coil in another way.

To diagnose, you need to take the following steps:

  • Open the cover that covers the cylinder;
  • Remove the cap of the high-voltage wire from the candle without unscrewing the part itself to maintain compression;
  • Tightly place a nail without a cap in the cap, it will simulate the central electrode of the candle;
  • Use a dielectric material to tie the cap with a nail to the cylinder so that the gap between the simulator of the spark plug electrode and the mass ranges from 5.5 to 7 mm (the exact distance for a particular model is recommended to be found in the user manual), but the part does not come into contact with the mass;
  • Using the starter to reproduce the engine start several times, holding the ignition button in the on position;
  • If a spark appears, you need to consider what color it is.
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A strong white or bluish spark is normal, and a faint flash of orange or yellow indicates coil failure.

Often, a cold magneto creates a powerful spark, but when heated, due to a defect in internal components, it does not conduct current. Once the mower coil has cooled, it starts up again and mows the grass with a fishing line or knife until the magneto heats up. This is abnormal behavior and the coil must be changed.

How the trimmer ignition system works

The ignition system of a two-stroke internal combustion engine consists of 2 elements: a flywheel and a coil (magneto). The figure below shows how they look.

The flywheel has an impeller that acts as a fan to cool the engine. Also on one side of the flywheel are permanent magnets, shown by an arrow in the figure.

When the flywheel rotates, an electric current is generated in the coil, which serves to produce a spark on the spark plug. A spark appears when the magnets are directly below the magneto.

Why do I need ignition adjustment

In some cases, when the engine does not start, ignition adjustment will be required. Of course, first you need to check the condition of the plug and the high-voltage cable with a cap.

It is necessary to adjust the ignition on a two-stroke engine in order to ensure timely ignition of the fuel in the engine combustion chamber. Below is a diagram from which you can understand the principle of operation of the internal combustion engine.

The spark in the plug should appear at the moment the fuel is compressed by the piston, when it does not even reach the top dead center (TDC). When the piston passes TDC, the fuel mixture ignites, as a result of which the piston goes down under the action of the explosion energy.

Therefore, if for some reason (mainly due to the displacement of the flywheel on the shaft relative to its initial position), the fuel ignites before the piston passes TDC, then it goes back, and the crankshaft rotates in the opposite direction. This movement can damage the starter assembly, cut the starter cord, etc. In this case, early ignition of the fuel occurs.

There may also be a late ignition on the trim: the piston, after the compression of the fuel that has not ignited, goes down, and at this moment a spark appears. In this case, the engine will either not start, or it will significantly lose power and it will be difficult to gain speed.

But such problems with early or late ignition on two-stroke internal combustion engines are quite rare, since the flywheel with magnets is already installed in the correct position, which is perfectly synchronized with the movement of the piston. In addition, the flywheel is secured to the shaft with a key and nut. Therefore, incorrect installation of the part is excluded.

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Trimmer ignition setting

Gasoline trimmers use both two-stroke internal combustion engines (ICEs) and four-stroke ones. But the ignition system in them is no different from each other, therefore, the repair and adjustment of this fuel ignition system will be the same for different types of internal combustion engines.

How the trimmer ignition system works

The ignition system of a two-stroke internal combustion engine consists of 2 elements: a flywheel and a coil (magneto). The figure below shows how they look.

The flywheel has an impeller that acts as a fan to cool the engine. Also on one side of the flywheel are permanent magnets, shown by an arrow in the figure.

When the flywheel rotates, an electric current is generated in the coil, which serves to produce a spark on the spark plug. A spark appears when the magnets are directly below the magneto.

How to check the health of a magneto

Magneto is the main part in the engine ignition system and is a coil with primary and secondary windings located around the core. Often, due to a malfunction of the magneto, the spark on the spark plug disappears and the fuel does not ignite. To check the coil, you will need to use a tester and follow these steps.

  1. On the tester, after switching to the resistance measurement mode, you need to set 200 ohms. In this way, the primary winding will be checked.
  2. Connect one electrode of the tester to coil ground and the other to the contact coming out of the magneto. Normally, the resistance should be between 0.4 and 2 ohms.
  3. To check the secondary winding, you need to set the device switch to 20 kΩ. Further, one probe of the device is inserted into the candle cap, and the second is connected to the “mass”. Normally, resistance indicators should be in the range of 4-6 kΩ and above (depending on the model).

If you do not have a tester, then you can use the following method, being very careful so that the electrode does not touch the cylinder, otherwise the coil will burn out.

  1. Remove the cap from the candle. The candle does not need to be twisted to maintain compression.
  2. It is necessary to insert a nail without a cap into the cap. The nail should be of such a diameter that it adheres well to the cap.
  3. Attach the nail cap to the cylinder using a dielectric so that the gap between the electrode and the cylinder body is between 5.5 and 7 mm (but never touches the “ground”).
  4. Using the starter, simulate engine start several times. The ignition button must be on.
  5. Observe if a spark appears and what color it has.

Normally, the spark should be strong, white or bluish in color. If the spark is weak, and its color is orange or yellow, this indicates a faulty magneto.

You should also consider the fact that sometimes cold magneto can give a good spark. But after heating, due to internal faults, it ceases to produce current. As soon as the coil cools down, the trimmer starts again and runs for a while until the magneto warms up again. This coil must be replaced.

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Trimmer ignition setting

Gasoline trimmers use both two-stroke internal combustion engines (ICEs) and four-stroke ones. But the ignition system in them is no different from each other, therefore, the repair and adjustment of this fuel ignition system will be the same for different types of internal combustion engines.

Typical malfunctions and ways to eliminate them

Now let’s look at the main malfunctions of magneto:

  1. Failures in sparking. There may be several reasons, as well as ways to solve them. This is oxidation or burning of the contacts, violation of the clearance adjustment, wear of the chopper lever pad, a punctured capacitor element. Failed elements must be replaced, and the adjustable clearances must be adjusted. If the problem is in the contacts, they need to be changed or cleaned.
  2. No spark. The reason may be a break in the transformer wiring, a short to ground, or a breakdown of the insulating layer on the high voltage cable. If the problem is in the transformer, then the node changes, if the short circuit, then it should be eliminated, and if the reason is insulation breakdown, then the cable just needs to be changed.
  3. If the spark is too weak, then most likely the reason lies in a broken capacitor, which will also need to be replaced.

Disassembly and assembly instructions for magneto

To repair the magneto, it must be dismantled and disassembled, for this, follow these steps:

  1. First, the device is removed from the power unit.
  2. The unit must be thoroughly cleaned of dust, as well as traces of engine fluid, if any. Magneto will be dirty, so it needs to be cleaned. Do not allow dirt to get on the internal components when disassembling the device.
  3. The next step is parsing. Using a socket wrench, it is necessary to unscrew the nut that fixes the ignition timing machine. Dismantle this element, then remove the key from the groove.
  4. Then move the latch slightly to the side, after which you can dismantle the cover of the interrupter unit. To remove it, unscrew four more bolts that fix it.
  5. When the cover is removed, the rotor can be removed from the housing itself.
  6. The final step will be to unscrew the studs that fix the transformer unit. By doing this, the transformer can be removed from the case. This gives you access to the constituent elements of magneto. Now the mechanism is being repaired with the replacement of all failed components. For further assembly and installation of the magneto, all the steps described above will need to be repeated in reverse order.