• Marine Mechanical Ignition

    Troubleshooting marine ignition and starting problems will go much easier if you have a basic understanding of how all the components relate to each other and their specific duties. Overall, the system is similar to an automobile with a few exceptions. In a car, the frame serves as a pathway for the DC current to flow back to the battery or ground. Obviously, on a boat made of fiberglass this is impossible, even if the boat is made of metal this still
    isn't desirable since the flow of electrical current in such a moist environment can cause devastating corrosion. Another more important safety difference is that components located in the engine room are required to be "ignition protected." In other words, the components have to be manufactured in a way that will prevent them from arcing or producing a spark that could result in an explosion. That is the reason that parts for a marine engine cost more than normal automotive parts.

    The main job of the starting and ignition system is to provide a spark to the appropriate cylinder at just the perfect time to ignite the gasoline and air mixture.

    Now let's get started with a typical mechanical ignition system found on many of the older boats. In the diagram below you will see the basic components. This is just a representative example and the wire locations, colors and routing may be different on your particular boat. The best source for troubleshooting can be found in the wiring diagrams specific to your boat.

    Attachment 1276

    Batteries ON/Ignition Off
    Electrical current travels from the battery to the large terminal on the starter solenoid, then through the engine mounted circuit breaker to the instrument panel (red wire). Now the current passes through a fuse, or on larger boats, an ignition breaker on your DC panel and on to the Batt terminal on the ignition switch (purple/red wire).

    Engine Starting
    When the ignition key is moved to the start position, electrical current travels from the Batt terminal to the ST terminal on the ignition switch then via the yellow/red-stripe wire to the S terminal on the starter solenoid. With the starter powered the engine begins to rotate. Simultaneously, the normally de-energized R terminal on the starter solenoid is energized and provides 12 volts of current to the ignition coil through the purple wire.

    The ignition coil is essentially a transformer that increases the voltage received from the battery. Within the ignition coil are two sets of copper wire coils or windings, a primary and secondary. The primary winding normally has a few hundred turns of heavier copper wire while the secondary winding contains thousands of turns of smaller wire wrapped around a soft iron core. The ignition coil is filled with oil to help dissipate the heat that is generated by producing the voltage.

    The current flows from the purple wire through the primary winding inside the coil then through the small black wire to the breaker points inside the distributor. If the breaker points are closed, the current flows to ground producing a magnetic field in the primary winding. As the engine rotates, the breaker points open stopping the flow of current. This causes the magnetic field to collapse, which produces a high voltage in the primary winding and an even higher voltage in the secondary winding (minimum 20,000 volts). The huge increase in voltage is caused by the significantly greater number of turns in the secondary winding. Now the extremely high-voltage exits the coil through the large black wire at the top and travels to the center of the distributor cap.

    Attachment 1277

    In the distributor cap, the high-voltage travels along the metallic strip along the top of the turning rotor and is discharged to the appropriate spark plug terminal. From the terminal, the high-voltage current passes through the spark plug wire to the spark plug where it is discharged as a spark across the gap in the plug.

    Furthermore, in the distributor you may find a condenser. The condenser interacts with the coil in the production of the high voltage, but its primary job is to prevent the points from arcing as they open and close. Arcing will burn and pit the points greatly reducing their lifespan.

    Engine Running
    Once the engine starts, the ignition key is released and returns to the run or IGN position. This removes current from the yellow/red-stripe wire that connects to the S terminal on the starter so it disengages and stops. This action also removes power from the R-terminal and the feed to the ignition coil. Now current is provided to the coil via the purple wire from the IGN terminal on the ignition switch.

    You will notice a resistor inline with the purple wire attached to the IGN terminal. During starting the coil works very hard producing the high-voltage output which creates intense heat inside the coil. This heat is not conducive to a long lifespan for the coil. With the engine running the spark does not have to be as intense as during the start cycle so the voltage can be decreased lessening the workload of the coil. So to reduce the input to the coil, the 12 volt current from the IGN terminal passes through the resistor where the voltage is decreased to approximately 7-9 volts.

    Now with the engine operating the alternator is providing current to the system to recharge the battery. This is accomplished through the orange wire to the large terminal on the starter, then through the battery cable to the battery. Since this charging current is normally around 13 volts the current from the alternator also becomes the source of power for the ignition. The alternator's current travels the same path to the ignition switch that the battery's current traveled.

    Stopping the Engine
    When the ignition switch is selected OFF, current is removed from the ignition coil so no spark is produced shutting down the engine.

    High Voltage Path Through The Distributor
    So how does the high voltage get to the correct cylinder? It is discharged from the ignition coil to the center terminal on the distributor cap. If you remove the distributor cap, normally the first thing you will see is the rotor sitting on top of the distributor shaft. The rotor has a metallic strip that runs across the top to provide a path for the high voltage current to follow. In the center of the rotor, the metallic strip stays in constant contact with the center post of the distributor cap allowing the high voltage to flow to the end of the rotor. The distributor shaft is driven by a gear on the camshaft and as the engine rotates so does the rotor. As the rotor rotates past each spark plug wire terminal, the high-voltage jumps across the small gap and travels through the spark plug wire to the appropriate spark plug where the spark is generated.

    Ignition Timing
    The timing of the ignition coil's discharge has to be precise to coincide with the correct cylinder as it approaches top dead center (TDC) of the compression stroke. The exact procedure for timing an engine is beyond the scope of this article and you will normally find the procedure outlined in your service manual but we will discuss a few points that relate to the components of the ignition system. When you are setting the timing, you are adjusting two parameters, dwell (how long the points remain closed) and timing (when should the points open).

    If you recall, when the breaker points open the coil discharges the high voltage to the distributor cap. But what causes the breaker points to open? The points have an arm that rests against the distributor shaft and the point where the arm touches the shaft is not round but instead lobed. As the shaft turns the lobe pushes against the arm opening the breaker points. The distance the breaker points are opened is referred to as "the gap" and can be adjusted by loosening the breaker points assembly and turning a gap screw. This adjustment can be made using a feeler gauge or more accurately using a dwell meter. Dwell is the amount in degrees of cam rotation that the points remain closed.

    Determining when the points open is known as "setting the timing" and requires the use of a timing light and timing marks on the vibration damper, or on the flywheel of the engine. While the engine is running the timing light is aimed at the timing marks. The light produces a strobe each time the spark plug fires. To adjust the timing the distributor hold down bolt must be loosened, and the distributor rotated until proper timing marks are aligned.

    Spark Advance
    When the spark plug fires the fuel/air mixture is ignited but not all at once, instead it begins burning at the tip of the spark plug and flame front advances outward in all directions (think of the rings produced by dropping a stone in the water). The speed at which this fuel/air mixture burns is relatively constant. For the engine to operate efficiently the spark plug must fire before the piston reaches the top of its travel to allow the flame front to propagate and build the pressure necessary to force the piston down the moment it reaches the top of its travel. However, as the engine speed increases the speed of the flame front does not change, so the spark plug has to fire sooner. This is accomplished by varying the timing using a centrifugal advance.

    Attachment 1459

    If you lift the breaker points plate assembly out of the distributor you will see a set of flyweights and springs. At slow speeds, the springs resist the force of the flyweights, but as the engine speed increases the flyweights overcome the spring force and adjust the upper shaft's alignment. This action increases the advance of the ignition timing causing the fuel/air mixture to be ignited sooner.

    Hopefully this mechanical ignition primer will help you understand the basic principles and aid in your troubleshooting.
    Letocha and Marc like this.


    Comments 8 Comments
    1. ben2go's Avatar
      ben2go -
      If you are still running points and condenser,there is a better way.More reliable too.Pertronix makes kits to replace points.They require less voltage and more accurately fire the coil during each timed ignition event.They are just as easy to install as points,but some require removal of the distributor.Instructions are included on how to remove the distributor without loosing your ignition timing.It's still good practice to check the ignition timing with a quality timing light.A couple horsepower can be obtained by making sure the ignition timing is spot on.I've used Pertronix products in a lot of autos and boats.Never had any issues.I picked up a couple mpg in my 1971 Buick Skylark when I changed the points out to a Pertronix unit and coil.

      You may need the number off of the distributor to get the correct unit for your engine.
      Amazon.com: pertronix: Automotive

      If you can't find your distributor listed,contact Pertronix.They can help match up your distributor to there ignition unit.
      Pertronix Performance Products

      I know I sound like a salesman.I am not and I am not affiliated with Pertronix.I have used their products without issues.
    1. TimG's Avatar
      TimG -
      Ooh I love the Pertronix kits, the best part was the ease of starting after installing those. However I happen to have a pair of distributors that Pertronix does not and will not manufacture the electronic conversions for so i am stuck with the old style...bummer
    1. ben2go's Avatar
      ben2go -
      Quote Originally Posted by TimG View Post
      Ooh I love the Pertronix kits, the best part was the ease of starting after installing those. However I happen to have a pair of distributors that Pertronix does not and will not manufacture the electronic conversions for so i am stuck with the old style...bummer
      Is there nothing that will cross over?They didn't make them for AMC engines back in the day,but a GM unit from the early 70's crossed over since the distributor was made by Delco basically GM.Have you tired MSD?They make some retro fits using GM HEI technology.Those a really reliable also,but they can get pricey.
    1. TimG's Avatar
      TimG -
      Ummm I believe its the Mallory YL670AV that I have and that is one of the few that they showed no support for.
    1. ben2go's Avatar
      ben2go -
      Quote Originally Posted by TimG View Post
      Ummm I believe its the Mallory YL670AV that I have and that is one of the few that they showed no support for.
      Have you checked for an upgrade or replacement?Mallory is usually an aftermarket upgrade.
    1. TimG's Avatar
      TimG -
      I did look into that once I realized they did not have the kits and found that I could replace the whole distributor. However the cost of the upgrade was more than I wanted to invest since I would have to buy two of them.
    1. ben2go's Avatar
      ben2go -
      Quote Originally Posted by TimG View Post
      I did look into that once I realized they did not have the kits and found that I could replace the whole distributor. However the cost of the upgrade was more than I wanted to invest since I would have to buy two of them.
      Two Mallory dist could run as high as $1400 depending on the engine make/model and the dist set up.They can be spendy.
    1. TimG's Avatar
      TimG -
      Yes if I remember correctly around $1200 was what it was going to cost for me. Just a bit too much.
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