See full version: Magnetos: Common Faults
The contact points which are mounted onto the end of the armature shaft, used to time the breaking of the primary winding current, will become pitted and worn, especially so if the capacitor is faulty. The result in high resistance will reduce the current flow in the primary winding and reduce the magnetic flux which adversely effects the secondary winding output voltage. more
The voltage generated across magneto coils is quite high, in the order of 20,000 volt if no spark plugs are in place. The coils are, of course, designed for this pressure but no insulation is perfect. A small number of electrons is ever present and over years or decades this flow carves out an ever widening pathway through the insulation. This expediential degradation may appear to be sudden when the fault occurs. Another problem, due to constant hot, cold, expansion, contraction, vibration or mechanical impact, is breakage of the fine winding wire. This will not stop the coil from working. The high voltage will simply arc across the gap. The gap will widen as the wire ends melt further apart and soon the adjacent turns will be affected so the coil will eventually fail. Magneto coils are usually a long time dying.
The original coil may be reusable, although it is susceptible to faults - as described in our section: common problems on magnetos. [links]
A short circuit absorbs all the power, hence no output or spark. With an open circuit the device has no CAPACITY to absorb the reaction voltage (back EMF) from the coil, therefore this energy is dissipated across the timing contact which quickly burns away. These faults do not necessarily occur instantaneously, they may develop over time leading to a gradual deterioration of the spark output.
Touch one probe tip to the engine block and the other to the metal clip inside the rubber casing which normally attaches to the spark plug. Readings are given in thousands of ohms, or "k" ohms. A good reading will range from 3 k to 15 k. A higher reading indicates a poor connection. [links]
Check the connection of the high voltage, or HV, wire to the coil and to the spark plug clip if you obtain a reading higher than 15 k. After making sure the connections are clean and unobstructed, retest.
Many small engines use a magneto to produce electrical current and spark. In such a system, a large, permanent magnet is embedded in the flywheel. As the flywheel turns, the magnet spins around a transformer with exposed copper wire windings, inducing a current which fires the spark plug and ignites the gasoline. The transformer is the magneto. Magnetos are most common in small outboard motors. They also are common in antique motorcycles.
Locate the magneto. It is the only part that has exposed copper windings. It will connect directly to the spark plug through a rubber casing. Pull the rubber casing off the spark plug. here
Set the multimeter into the ohms function, or just use an ohmmeter. Manually set the dial or button on the meter to the 40 k range. Do not use auto ranging, as it is unreliable with a magneto. [links]
Re: Mercury kiekhaefer 650 No Spark
I am new to the forum and hope i can learn and share any knowlegde that i have. I have aquired a mercury kiekhaefer 650. I have checked all the wiring diagrams and everything seems to be in order. Only thing is i am not getting a spark. It has a magneto on it. The wiring seems fairly simple. Only thing thats missing is the rectifier. Would this be anything to do with it not having a spark.
The only numbers i can find are: 3163 model 4d-4 on the magneto and 46298 on the block the same side as the magneto. Does this help?
Thanks [links]
You need the serial from the tilt tube. 650 started out using the old Mag setup, then in '66 it went to the Thunderbolt and then when the 650 went 3cyl it changed a little again..
Be extremely careful with parts 38 and 35, the cap and rotor. Mucho dinero! Follow Laddies directions above to remove the mag and clean all the contacts inside. When a motor sits, sometimes the brass contacts inside get the green corrosion. My motor sat for years and had no spark until I cleaned the mag insides. [links]
Re: Mercury kiekhaefer 650 No Spark
Cause
Confirmed the customer's complaint and found the engine did not start. Performed a visual inspection of the fuel system and ignition system components, but found no obvious faults. Removed the spark plugs and performed a visual inspection, but found no obvious faults. Connected an inline spark tester to the ignition coil secondary lead, started the engine, and found the spark was intermittent. Used a multi-meter to measure the resistance of the ignition coil and found the measured resistance was within specifications. Connected a lab scope to the ignition coil primary signal circuit, started the engine and found an erratic signal. Performed a visual inspection of the ignition control module wiring harness and connector terminals, but found no obvious faults. Key on, engine off, used the multi-meter to check for voltage and ground at the ignition control module and found both were present. Connected the lab scope to the ignition control module primary signal trigger input, started the engine and found the waveform revealed no faults with the primary trigger. This indicated the ignition control module was faulty.
Component Test Meter can be used to view secondary ignition waveforms. [links]
Clamp current Probe around the b+ side or the Control side of ignition coil. Do not clamp around both.
Still working on this issue, and thanks for the tips so far. I kept measuring the black lead on the magneto harness and was getting almost no resistance, so I pulled the magneto off. I realized that I can't measure the source coil resistance with the condenser in series, so I removed the condenser.
I stuck sandpaper in between the points to keep them open and measured. I got 1.8 to 2.0 ohms versus the manual's 1.7 for the source coil (70 F in the garage) so I am considering the coil good. I replaced the condenser since I had a new one. The new one measured .260 uF which is close enough to the manual's .25 uF. I reinstalled the magneto, taking care regarding the wire routing (took a pic for reference before I took it apart). Bolted it back on, installed the flywheel, and set the points to 0.35 mm or .014" when open. Points appear to open and close properly when rotating the crank.
Shouldn't we have gotten a spark? more