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How to Change Coils and set points on old OMC's

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  • How to Change Coils and set points on old OMC's

    Here's a quick how-to for folks who are interested in tuning up their old OMC outboards from 3 to about 25 horsepower with the universal magneto which is common on '50's on up into the '70s OMC outboards (johnson, evinrude, gale):

    First, you'll need to remove the flywheel.

    In order to do this, you'll need a $10 harmonic balancer puller from the local auto parts store, and GRADE 8 hardened bolts that are 1/4-20. (that's 1/4 inch by 20 threads per inch). They'll need to be about 3 or 4 inches long.

    Remove the flywheel nut. You'll usually need a 3/4 socket and breaker bar. The nut is right-hand (normal)threads so lefty-loosey as usual. Leave it on the crankshaft a few turns so when the flywheel pops off the crankshaft, it doesn't go flying off and bloody your nose!
    Make sure your flywheel puller (in this case a harmonic balancer puller) is mounted with the flat side up.
    You'll screw the 3 grade 8 bolts into the holes that are revealed when taking the ring off the flywheel that the pull starter pawls grab onto when starting.
    Thread the bolts in about a 1/2 inch, being careful not to go so deep that you screw the bolt into the coils underneath the flywheel.
    Now, slightly tighten up the puller bolt and make sure each bolt is screwed in equally so that the puller is pulling evenly on the flywheel.
    Then, tighten the puller bolt good and tight. It should pop off. Sometimes it helps to give the puller bolt a slight rap with a hammer. If it still doesn't come off, tighten the puller bolt a little more and be patient. Never beat on the flywheel or it will warp and be useless.
    When the flywheel is off, clean the crankshaft taper and the flywheel tapers. They must be clean and dry when reinstalling the flywheel---NO GREASE or ANYTHING on the tapers! And remember that you MUST use a torque wrench to reinstall the flywheel later or it will either ruin the crankshaft by overtightening, or let the flywheel key shear due to undertightening. If you don't know the torque specs., ASK!

    Here are some pics of the tools that are needed:
    Attached Files
    Last edited by jbjennings; February 19th, 2009, 12:53 AM. Reason: fix
    Not a certified mechanic but I have at least 2 shade trees in my yard and my wife always says I'm certifiable. So remember that when you follow my advice

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    Re: How to Change Coils and set points on old OMC's

    Now that the pesky flywheel is out of the way, you have easy access to the coils, points, and condensers.

    If your motor has been sitting for many years and the coils are cracked or otherwise nasty looking, don't waste your time ---replace 'em!
    It's really worthwhile in my opinion to replace the coils, condensers, points, and spark plug wires all at once. However, if everything looks good you might try cleaning and regapping the points and then testing for spark. The points must be spotless, not even a fingerprint. The typical points gap is .020 inches and typical spark plug gap is .030 inches, but check your specs. for your motor to be sure. If in doubt, ask.

    To remove the coils, there are 3 retaining screws. Remove them. Take out the coil and put your new one in, being careful to check to see that the wire core of your plug wire is not corroded if you're reusing wires. If it is, try to snip off a 1/2 inch or so to get to good copper core to push onto the pin of the new coil. Be very careful to look for any chaffing or cracking of the plug wires which might cause the spark to arc from the wire. Remember that the coils should fit flush on the mounting boss or they will stick out and the flywheel magnet will smash them on the way by! Make sure the coil wires and condenser wires are tucked out of the way of the flywheel, and work on one side at a time, in order to use the other coil assembly as a reference. A picture of the right and wrong way to mount the coil is provided below:

    Next, clean and adjust the points. If the points are charred or pitted, they need replacing. Use a feeler gauge to regap the points to .020. The gauge should come out easily, only a VERY slight resistance should be felt when taking the feeler gauge out from between the points. The points adjuster screw and other under-flywheel parts can be seen in the pics below. I've used 400 grit sandpaper to lightly sand the points but most places sell points files to do it right. Make sure you clean all the dust off the points.

    The condensers are pretty reliable but as with all electrical parts, they're not infallible---so you make the call as to whether you should replace them or not. They are fairly cheap to replace either way.

    Now that you've got new coils and such, I like to put the flywheel on and turn it by hand with the plugs out of the cylinders and check for spark before retorquing the flywheel nut. If you have good spark, reinstall and retorque the flywheel to specs. Recheck for spark with a spark tester. I also included a pic of my handy auto-zone $6 spark tester. Don't rely on spark appearance to determine if you have good spark! Use the spark tester to see if it'll jump a 1/4 inch gap with a nice blue pop!
    If so, you're in business!
    Good luck,
    Attached Files
    Not a certified mechanic but I have at least 2 shade trees in my yard and my wife always says I'm certifiable. So remember that when you follow my advice