Over-torqueing or cross-threading strips the threads on aluminum cylinder heads. With the right tools, one can salvage the head with a Heli-Coil or equivalent insert. Unfortunately, the cost of the installation tools is prohibitive for weekend mechanics, who may see a stripped head once in a lifetime. Spark-plug thread repair kits are specific to each [...]
Heat range depends primarily upon the exposure of the insulator to combustion heat. As shown in Fig. 3-14, the greater the exposure and the longer the thermal path, the hotter the plug. The plug should run hot enough to prevent fouling, but not so hot that it ignites the mixture early, before the spark (Fig. [...]
Now that leaded fuel is no more, spark plugs can be cleaned by soaking in carburetor cleaner. Sandblasting is out of the question, since the abrasive particles imbed themselves in the insulator where they fall into the cylinder once the engine starts. In passing, it should be mentioned that the jagged, blackish discoloration on the [...]
Solid-state systems have some built-in ignition advance by virtue of flywheel velocity. As rpm increases, signal voltage occurs earlier, since the flux field moves faster. But advance is linear and not tailored to engine characteristics. Digital control retards ignition during cranking to prevent starter-cord “bite” and advances timing in a patterned sequence that can be [...]
As the twentieth century drew to a close, transistorized magnetos gave way to capacitive discharge ignition (CDI) systems. As the name suggests, CDIs store electrical energy in a capacitor, which then discharges into the primary windings of an ignition transformer. Figure 3-12 illustrates the basic circuit. A flywheel magnet generates several hundred volts in the [...]
Much to the relief of mechanics everywhere, transistorized ignition (TSI) has become nearly universal. Transistorized magnetos substitute a Darlington transistor (actually a pair of transistors) for the contact points and condenser. Doing away with these troublesome components was the best thing that happened to small engines since the advent of loop scavenging. On the downside, [...]
Vintage magnetos employed a mechanical switch, called the contact points, point set, or breaker points, to turn primary current on and off. Some Honda four-strokes still use this archaic form of ignition. One of the contacts is fixed and permanently grounded to the engine. The moveable contact forms part of the primary circuit. When the [...]
Ignition and generating systems depend upon the interplay between magnetic lines of force, or flux, and electricity. This interplay can be described as follows: • Electricity is generated in a conductor when magnetic lines of force move through a conductor. The faster the movement, the greater the electrical potential generated. To make things more efficient, [...]
All engines have provision for adjusting the E-gap, or the distance ignition-coil armature stands off from flywheel rim. The narrower the gap, the stronger the magnetic field and the greater the voltage produced by the coil. Ideally, the gap should approach zero, but we must allow for bearing play, thermal expansion, and flywheel out-of-round. An [...]
If there is no or weak spark, remove the flywheel in order to check the condition of the key, which fixes the timing between flywheel magnets and the ignition coil. Keys shear or deform in response to sudden loads or as the result of insufficient torque on the flywheel hold-down nut (Fig. 3-1). The flywheel [...]
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