Obsolete Outboards

by Max Wawrzyniak - St Louis, Missouri - USA Bringing a 1956 Johnson 15 hp Back to Life Part III: Removing the Flywheel and Magneto

Part 1 - Part 2 - Part 4 - Part 5 - Part 6 - Part 7

Before we get started on the magneto, you might want to review the magnetos column.

Some people like to check for "spark" before they start mess'n with the magneto. Checking for spark means removing the sparkplugs from the cylinder head, gounding the outer metal casing of the sparkplug to a good "ground" (bare metal) somewhere on the engine, and with the spark plug wires still attached to the plugs, cranking the engine with the recoil starter or with a piece of rope wrapped around the flywheel. If everything is working correctly you should be able to see the plugs sparking and also hear an audible snapping sound. A white spark or blue spark is preferable to a yellow spark.

SF17 - "Inspection" hole in flywheel through which you can check for cracked coils. You can also adjust the ignition points "gap" (we will get to that) through this hole. (click images to enlarge)

I don't bother with checking for spark before tearing into the magneto. If I intend to run the engine myself (and I rarely work on other's engines) then I want it to have a tune-up. The cost of putting new ignition points and condensers, new spark plugs, and maybe new spark plug wires into one of these old OMC outboards is usually no more than about $25.00 assuming you buy the parts and install them yourself. When you pay a shop to work on your outboard you will usually end up paying full retail price for the parts, but with a bit of shopping you can often buy the parts (to be isntalled by yourself) at a discount, which means you not only save the labor charges but also save a little on the cost of the parts themselves. Replacing these items, which are more-or-less considered "expendables" or "consumables" will save you some frustration when it comes to getting the engine into running condition and will also give you a better-running engine.

As mentioned in the Magnetos column, the one area of weakness in all 1 and 2 cylinder OMC engines manufactured from about 1951 until the late 1960's are the magneto coils. These coils, which resemble round plastic cylinders, always go bad, without exception. If your engine has the original coils, it is a sure sign that the engine has seen very little running (if any) in recent decades, and the coils will have to be replaced. Many OMC outboards you will run across, however, will have already had the coils replaced and as the replacements rarely go bad you can run them.

With the recoil (pull rope) starter removed, look to see if there is an inspection port (hole) in the top of the flywheel; most all of the old OMC outboards of under 25 hp had this hole. Usually it had a sheet metal cover although often the hole cover is missing. Have a look down into this hole as you slowly rotate the flywheel by hand (OSHA would have you remove the spark plug wires to be sure the engine does not start while you are turning the flywheel. Yea, right. Removing the spark plugs as well makes the engine easier to turn - no compression). You will see the two cylindrical plastic coils which may be green or red or purple or maybe some other color. If there are cracks evident in the plastic, you have bad coils even though you just might still get a spark out of them. No cracks, and the coils are PROBABLY good. Replacement coils can be had at Johnson and Evinrude dealers or aftermarket Sierra coils (part # 18-5181) can be purchased through any boat dealership or through NAPA auto parts. The Sierra coils list for about $21 each and sometimes the boat dealers will discount them a little. By the way, only turn that flywheel clockwise, looking down on it. Otherwise you risk damaging the water pump impeller you just installed.

In order to go any further, one (you) must remove the flywheel. The proper way to lossen the flywheel nut is to hold the flywheel stationary with a big strap wrench while loosening the nut with another wrench. I don't have a strap wrench big enough to go around the flywheel so I put a box-end wrench (better than an open end wrench, and a six-point box is better than a 12 point box; if you don't know what I am talking about, do a Google search) and give it a persuasive tap with a hammer while holding the flywheel still with the other hand which also holds the wrench from sailing.

SF19 - The puller in place on the flywheel: note that the puller mandrell (center big screw) is in line with the engine's crankshaft, that the (3) smaller bolts are threaded fully (but not excessively) into the (3) holes in the flywheel; that the flywheel nut has been "backed-off" a few turns but is still on the crankshaft and lending support to the crankshaft (but the nut is NOT taking the thrust from the puller directly). The orange handled handled screwdriver is to keep the flywheel from turning as the mandrell is tightened.

Loosen the nut a few turns but don't remove it: leave it threaded onto the crankshaft (which is what the flywheel is bolted to) and set-up your flywheel puller. If you don't have a flywheel puller you are going to need to borrow one or buy one. While I don't intend to endorse any one tool source over another, something like this will work just fine.

You might need to stop off at the hardware store if the bolts for the "legs" that come with the puller are the wrong diameter to thread into the three holes in the top of the flywheel. You do NOT want to use a puller that lifts up on the other rim of the flywheel as that may damage the flywheel. the puller MUST pull from the three threaded holes on the top of the flywheel.

SF20 - The flywheel has been removed, revealing the magneto. The coils do not appear to be cracked and we will assume that they are "good." If you are only replacing the ignition points and condensers there is not need to remove the magneto from the engine. I would strongly suggest, hwoever, replacing the spark plug wires with new metallic core (not graphite) wires if the old ones appear to be stiff and brittle or are cracked, in which case you will need to remove the magneto from the engine. Note the little sheet metal clip that can be used to disconnect the htrottle linkage that rotates the magneto for "spark" advance.

Thread the three bolts down through the puller and into the three holes of the flywheel as shown in above. The bolts must be fully-threaded into the holes, but if the bolts are threaded so far into the flywheel that they protrude underneath, and if the flywheel is then rotated, the bolts can damage the ignition components under the flywheel. Once the puller is installed, do not allow the flywheel to turn. The puller is tensioned by turning the large threaded center mandrell (bolt), the bottom of which has a pointed do-dad on it which will self-center in the center depression machined into the end of the crankshaft. The flywheel nut should remain on the crankshaft threads to help support the crankshaft but the puller should bear against the crankshaft and not the nut. Be sure that the nut is loosened a few turns, however.

I use a large screwdriver inserted into the legs of the puller to keep the flywheel from turning as I tighten the mandrell, but the proper tool to use is that big strap wrench which I don't have.

SF21 - The (4) screws marked #17 are the screws that secure the magneto to the engine. The item marked #15 is the clip for disconnecting the throttle linkage so that the magneto can be removed. Although this linkage may be different on some larger engines, the arangement of the rest of the magneto components is common to all 2-cylinder OMC outboards manufactured from about 1951 until the early 1970's.

Make sure that the mandrell of the puller is in-line with the crankshaft and not leaning one way or the other.

The flywheel is seated on a taper machined into the end of the crankshaft and if the flywheel has not been off in a long time, it may take considerable tension to break the flywheel loose from the crankshaft. How much tension is difficult to quantitfy. In other words, I don't know. What I do is to screw-down the mandrell of the puller as much as I dare. If the flywheel has not come loose yet, I will lift up on the flywheel and give the top of the mandrell a persuasive tap with a hammer. If you grab the flywheel and lift up on it, you will notice a tiny bit of "end play": the flywheel and crankshaft will move up and down a very tiny amount, maybe a couple of thousanths of an inch. Have someone lift on the flywheel so that the flywheel is at the upper end of it's end play, and hit the top of the puller mandrell with a hammer-blow straight down. Often this will break the flywheel loose. Do NOT hit the puller with the hammer unless the flywheel is being lifted, and make sure the hit is square and straight. I don't know how to tell you how hard of a hammer blow I give the puller, but it is certainly not a "timid tap" nor is it "everything I've got." If a couple of hammer blows don't free the flywheel, put the hammer aside and give the mandrell maybe another 1/2 turn or so and then try the hammer again.

If a few hammer blows have not freed the flywheel and you dare not put any more tension on the puller, soak the crankshaft with penetrating oil (WD-40 is not prenetrating oil) and let it sit over night.

If it still will not come loose, use a propane touch (like is used for soldering copper pipes) and rapidly heat the flywheel around the crankshaft while trying to avoid heating the crankshaft too much, all the time keeping the puller under tension. After heating the flywheel for several minutes, put the tourch down and try the hammer again.

Some combination of all of the above should free the flywheel. If the flywheel hase been recently removed, it may come loose easily with no need for hammers or tourches or oil, but if it has been stuck on that crankshaft for 40 or 50 years. you may need to use all of the above in order to get it loose. By the way, a really stuck flywheel will make one heck of a "bang" when it pops loose.

SF23 - Removing the magneto: loosening the (4) screws marked # 17 in Figure SF 21. Note that the throttle linkage has been disconnected.

Once the flywheel is removed you are looking at your magneto (Figure SF 20). Each of the two cylinders has it's own coil, ignition ("breaker") points, condenser, spark plug wire and spark plug. Other than some magnets embeded in the rim of the flywheel, and a cam (eccentric) on the crankshaft that acts upon the points, that is all there is to the magneto and the whole ignition system (figure SF 22). I highly recommend that you replace the ignition points and the condensers at a minimum and these items can be changed-out with the magneto remaining on the engine.

If the spark plug wires look old and have turned hard and/or have cracked, it would not be a bad idea to replace those as well, and for that the magneto needs to be removed from the engine (which is not a big deal). The magneto also needs to come off if you have cracked coils which need replaced.

The magneto can be rotated back and forth and this is how the igntion timing is advanced and retarded as the engine is speeded-up and slowed down. The rotation of the magneto is controled by an arm and bellcrank arangement on the port side of the motor and there is usally a sheet metal clip which can be removed without tools in order to disconnect this linkage (figure SF 20). Four screws (#17, Figure SF 21) are loosened and then the magneto can be lifted up off of the engine. Be carefull that the arms for the ignition points do not "hang-up" on anything while you are lifting the magneto off the engine. The only wires hanging off the magneto will be the (2) spark plugs wires, unless you have a "push to stop" button in which case you will also have two small wires. The small wires usually have disconnects which are often hidden beneath little plastic sleeves on the wires.

Since I keep reminding myself not to make any assumptions about how much the reader knows, this is getting a bit "wordy." and so the magneto work will drag on into next month's column as well.

Bye Bye

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