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by Max Wawrzyniak - St Louis, Missouri - USA

Bringing a 1956 Johnson 15 hp Back to Life

Part IV: Magneto Work

Part 1 - Part 2 - Part 3 - Part 5 - Part 6 - Part 7

Have a good look at figure SF 25 (below). This is your magneto. This is the thingy that makes the spark plugs spark. In the very center is the crankshaft (which you will not see on your magneto if you have already removed the magneto from the engine. Instead, you will see a hole where the crankshaft fits). Doo-dad #4 is a cam (eccentric) which is a slip-fit on the crankshaft. As the crankshaft rotates, the cam alternately opens and closes the ignition points ("breaker" points) which are #'s 10 and 20. You will see the spring-loaded rocker arms which ride on the cam, and which have the points at their outer ends. We are going to install new points, but just as an "FYI," the most common problems with old points are that their contact surfaces are dirty and/or pitted and eroded. You can "clean-up" pitted points with a special little points file or a bit of emory cloth, and you can clean dirty points by allowing the points to close on a bit of clean business card and pulling the card out from between the closed points several times. Other problems that occasionally show-up are weak return springs and bent points rocker arms. Have a look at figure SF 26 for some other protential problems. Since most of these parts are pretty cheap and you already have the engine apart, I suggest just replacing the points and condensers. Why screw with trouble-shooting old parts?

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SF25 - The magneto and it's parts

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Numbers 2 and 13 on figure SF 25 are the condensers, which have nothing to do with steam as their name suggests. Some have commented that a more appropriate term would be capacitor. Anyway, the condensers act as short-term (very short-term, like a fraction of a second) electrical current storage devices. Sort of like a battery, but different. I won't go into more detail because it will bore you and you don't need to know more about condensers than I have already written, and also because I really don't remember much more about condensers and would have to look it up. I do remember that condensers can fail in two different ways. Notice that the condenser is a little metal cylinder with a wire sticking out the end of it. One way the condenser can fail is for there to be short circuit between that wire and the metal case of the condenser. This is easy to check for if one has a multi-meter or even a little battery-powered test light. There should be no electical connection between the metal case and the wire; if there is, the condenser is shorted and junk. The second way a condenser can fail is that it can have an internal problem that makes it weak or ineffective. One needs a special testing device for detecting this problem. But condensers for our favorate old OMC outboards from 1955 to 1972 (are so) are dirt-cheap to buy so why bother with testing old condensers at all? Just replace them.

SF26 - Yeah, you've seen this before. You know, you can replace most of this stuff pretty cheaply and then you don't have to trouble-shoot problems with it.

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Numbers 5 and 16 on SF 25 are the coils. As with the points and condensers, there is one for each cylinder. The coils are cylindrical plastic things mounted on the middle "leg" of a three leg metal thing constructed of many layers of metal riveted together. The plastic coils and the laminated metal are considered a single component in these old OMC engines, although with other brands of engines one could replace the plastic coil separately from the laminated metal thing.

The coils orignally installed in these old OMC engines always went bad, without exeception. If the coils on your engine have cracks in the plastic casing, they are bad. No cracks, and probably your engine has had replacement coils installed and most likely they are good. Uncracked coils can go bad but it is rare, and anyway the only way to test them is to use a special testing device, which you don't have. You can spend a lot of money buying one... or if you are handy you can try building your own coil tester... or you might be able to take your coil to a local small engine/outboard motor repair shop and have them test it for you. I just assume that if the things are not cracked, they are good, and I don't give them a second thought unless I have already replaced the points, condensers, spark plug wires and spark plugs and still do not get a spark.

click to enlargeSF27 - How to install the spark plug boots on the ends of the spark plug wires. Make sure that the pointed end of the coiled wire goes through the center of the spark plug wire so as to make contact with the wire core of the spark plug wire. Disregard #5; you won't have a choice like the old boys did 50 years ago. The "slip-one" end is the only end available on Champion J8C plugs (or equivalent) , which are the plugs recommended for most 1950's and 1960's OMC outboards of under 35 hp or so.

What about them spark plug wires? Chances are they are the orginal wires and that they are getting old and stiff and cracking. Unless you are real sure that the wires have been replaced at some point in the recent past, I would go ahead and replace them. They could have some small cracks that could cause short circuits and could drive you nuts trying to track-down the problem. I try to minimize frustrations in my life, so I always replace the wires. You will need some metallic-core spark plug wire, which you can usually buy by the foot. I use Sierra-brand spark plug wire, which I bought a while back in a 100 foot reel - part # 18-5226. Sierra also sells a package containing 25 feet of wire and a bunch of useless (to you) fittings, part # 18-5225. Since you will need a lot less wire (measure the lengths of your old wires, allow a bit extra, and note that the wires are of different lengths), try calling local boat dealerships and small engine repair shops and you will find people selling this stuff by the foot. There are other brands, of course, but do not get talked into buying graphite-core wire. Before you close-out the PDF, note the spark plug boots, 18-5750. I always re-use the old boots on new wires, unless the old boots are torn.

The spark plug wires are removed from the coils by simply pulling on the wires; there is a little spike inside the hole in the coil on which the wire is impaled. The rubber boots on the other end of the wires can also just be pulled off but try not to tear the rubber. Note the little wire scroll inside the boot; it is a seperate piece and not molded as part of the boot. Figure SF27 shows how to install the boots on the new wires. Note that #4 recommends the use of a special silicone lubricant to make installing the boot easier; it is really really hard to get one of these boots on without some kind of lubricant. I usually use an ordinary silicone spray lubricant , but have on occasion used a drop of 2-cycle motor oil. Don't use too much lubricant. Also, disregard # 5 on SF 27; times have changed and one no longer has a choice of terminals on one's spark plugs. By the way, the spark plugs to use on this 1956 15 hp. and on virtually all 1950's and 1960's OMC's are Champion J8C or equivalent.

SF28 - You have to remove stuff from the underside of the magneto in order to remove the spark plug wires. The plug wire for the top cyclinder is usually marked with a little metal band; keep track of which wire is which.

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If you are installing new coils or if you are temporaily removing the old coils in order to install new sparkplug wires on them you will need to remove some of the hardware from the bottom of the magneto ("stator") plate. I really suggest taking careful notes and even photos as these stator plates often are used on several different models of engines and so often have extra holes which may make reinstalling the bits and pieces more complicated than you think. I find it helpful to put the screws back into their holes as soon as a part is removed, rather than tossing all the screws into a coffee can and then later trying to figure out which screw went where.

Once the "gingerbread" is off the bottom of the magneto/stator, you can flip it right side up and loosen screws #3, 8, & 18, figure SF21, plus one screw on that diagram which excaped being numbered. Note that in additon to the fat sparkplug wire on the bottom, each coil also has a small wire attached under one of it's mounting screws (a ground wire) and another small wire that attaches to the ignition points under a screw which also holds the wire from the condenser. Unfasten these small wires and lift the coils off the plate. If you are reusing the old coils, pull the spark plug wires out of them and push your new spark plug wires (cut to the appropriate length) into the hole and secly onto the little spike inside the hole. Note that there should be a little rubber boot covering the joint where the spark plug wire connects to the coil- be sure to re-install the little boots.

Here's something important: make sure you know which spark plug wire goes to which cylinder. usually there is a little metal tag on the "top" spark plug wire- be sure to transfer it to the new wire. What happens if you lose track of which is which? Figure SF25 provides some helpfull hints. Also, if you try to start an outboard with the spark plug wires reversed (and everything else is correct) it will back-fire and yank the starter cord violently out of your fingers.

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SF29 - Stuff removed from underside of magneto. I always put the screws back into their holes. Makes keep track of which screw goes where a lot easier, and lessens the chance of losing a screw.

When re-installing the coils to the magneto (stator) plate, one has to set the "air gap": No big deal at all, actually; the "air gap' is the distance between the laminated metal "heels" of the coils and the inner circumference of the flywheel. The flywheel contains magnets, and the goal is to have the coil heels as close to the magnets as possible with out actually rubbing on the spinning flywheel. To set the air gap, one merely loosens the coil mounting screws and moves the coil around until the outer surface of the heels is flush with a machined surface on the stator plate directly below the heels. Figure SF30 shows the heels and the surface directly below the heels; just rub your finger across the joint between the heels and the machined surface and if you feel no "step" as your finger crosses the joint, tighten the coil mounting screws and re-check to make sure the coil has not moved. Once the coils are mounted you can put the "gingerbread" items back on the bottom of the magneto.

With the magneto right-side up, the condensers can be removed. Have a good look at figure SF30 and SF31: remove the screw from the points which holds the wires from the coil and condenser (and the wire from the kill switch, if your engine has a kill switch). Then remove the single screw which secures each condenser.

click to enlargeSF30 - Setting the coil "air gap" just means making sure that the outer ends of the coil heels are flush with the machined surface directly below them. The holes in the coils for their mounting screws are slightly over-sized so that the coils can be moved around slightly to make this alignment.

Now to the ignition points, AKA "breaker points" or just "points." The points are actually in two pieces: a "base plate" and a "rocker arm." The actual contact surfaces of the points are two tiny round metal disks, one of which is mounted on the stationary base plate while the other is mounted on the rocker arm, which pivots on a little axle or shaft. The points are spring-loaded to be in the "closed" closed position (contacts together) and the cam rotating on the crankshaft moves the opposite end of the rocker arm to "open" the points. Although you can buy points and condesners seperately, I would suggest that you buy a tune-up kit, which includes (2) points rocker arms, (2) points base plates and (2) condensers. You need one kit per engine, and you can either get the official OEM kit from a Johnson or Evinrude dealer, or you can buy a Sierra brand kit from virtually any boat dealership (regardless of what engine brand they carry0 and also from NAPA auto parts stores. The Sierra kit I used on the 1956 15 hp was part # 18-5006, which also fits the 5.5 hp, 7.5 hp, and 10 hp models of the 1950s and early 1960's, and also 18 hp up to about 1961, and a few other models as well. List price for the kit is about $20.00

Remove the tiny wire clip which holds the rocker arm onto the littlte shaft that it "rocks" on (needle nose pliers work well here). Notice also that there is a flat sheet metal clip (usually copper colored) which secures the spring that holds the rocker arm in the "points closed" postion; this clip needs the be removed as well and then the rocker arm can be lifted off. The rocker arm shaft is part of the magneto stator plate and does not come off. Remove the single screw which secures the points base plate and then lift off the base plate. Note the "adjuster" for the base plate; this looks like a screw but it is not. It is a permanent part of the magneto stato plate and it is not removed.

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SF31 - The various parts of the "points," along with the "adjuster", which is used when setting the points "gap."

You can now install the new points base plate with it's single retaining screw and place the new rocker arm on it's pivot shaft: use the other cylinder's points as a guide to make sure you have the rocker arm placed correctly. Install the (2) little clips for the rocker arm shaft. You can then install the new condenser and secure the wire from the condenser, the wire from the bottom of the coil (and the kill switch wire, if you have one) under the little terminal screw on the points base plate.

Replace the points and condenser for the other cylinder and the magneto is now ready to be reinstalled on the engine, but let's wait until we have the carb work down before putting the mag back on. That will give use a bit more room to work with.

One last comment before closing for this month: you may have noticed (2) little red capsules that resemble cyanide capsules that came with the tune-up kit. Those are not to put you out of your misery if you screw-up something. Now, you might actually want to use them although I never have. More on the capsules next time.


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