Splitdorf lo and hi-tension magnetos

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Splitdorf lo and hi-tension magnetos

Postby Jewarjone » Wed Oct 11, 2017 10:54 pm

Splitdorf Magneto wiring and determining firing order and setting the timing.

I have a 6 cylinder 1910 Mitchell with the low tension (Magneto is really a generator of low voltage (6-8volts)Splitdorf set up. I had a 1910 EMF 4 cylinder with the same set up and they both worked well The original 6 volt hi tension coil was burned out on the Mitchell because the previous owner used a 12 v battery for his headlights and when he wired the coil from that battery he burned up the old 6v coil. I bought a modern 6 v coil and fitted it inside the old coil box with a condenser which I grounded to the block ( with the ground wire already running to the base of the magneto). it works great!

If you have this low tension early magneto, the above will work and the drawings below should be helpful.

If you have a Dixie Splitdorf with an impulse coupling they usually wind up the spring coupling with a clockwise twist of the input shaft. Rig up a piece of bare hardware wire that will clamp under the terminal at 2 o’clock as you look at the mag from the front( input shaft end) and bend it in an arc over to the side of the mag to it’s the base on the right side of the mag leaving a gap of about .020-.025” Roll the mag until it winds up the impulse spring and then snaps and when it sparks that is now your # 1 plug wire terminal. Mark the cover on the back with a pencil with a number 1 next to the terminal.

If no spark or a weak spark you might take the cover of of the back of the mag which should expose the points. Take a small strip of fine 600 grit sand paper and fold it over with the grit exposed on both sides. Roll the mag until the points open ( they should open about .010”) and then insert the folded sandpaper between the points. Roll the mag until the points close and then gently pull the sandpaper out from between the closed points. Do this twice and this will remove dirt and oxidation from the points making for a much better contact. While you have the point cover off, take a small screwdriver and put a small amount of axle grease on the little cam’s surface that actuates the points. Oil the mag shaft bearings with 30wt motor oils and you should be good to go if it throws a good spark! If not you likely need a new coil and condenser and that is a job for a trained magneto rebuilder!

Be sure that the mag , when viewed from the input shaft end, turns in the same rotation as your engine (and winds up the impulse coupling) does when you crank it ( usually clockwise when facing the front of the engine). If not, you need to find a mag that does! The hi tension distributing rotor in the mag rotates opposite of the input shaft so the next firing terminal will be counter clockwise from the front or input shaft end of the mag in the 10 o’clock position . If you know your engines firing order you can now hook up the hi tension plug wires in that order.

If you do not know your engines firing order. Take the spark plugs all out and put a small wad of paper towel on the first cylinder’s spark plug hole ( the one closest to the front of the engine). Roll the engine slowly with the crank until the paper pops out of the hole. You are starting up on the compression stroke of the number one cylinder. Find a piece of heavy wire ( gas welding rod or wire coat hanger) and cut off about 10 “. Insert the wire into the plug hole and bend it a little so you can use it to “feel” the top of the piston or at least reach partway into the bore. Hold the crank with your left hand and the wire with your right, roll the engine slowly and you should feel the wire being pushed out of the spark plug hole as you very slowly move the crank. When the wire stops moving up move the crank a little more and it will feel like the piston is not moving. You are on or a little past top dead center. Leave the crank alone now and set your magneto on the engine’s mounting base. Then loosen and adjust your coupling so that the spring is wound up and the coupling is at the point where it is at the verge of snapping and firing a spark against the base of the mag. Tighten the mag coupling to the engine output shaft and bolt the mag down. Now go back to checking that the number one terminal wire will spark when you roll the engine up to top dead center. If not loosen the mag coupling and move it enough so that the impulse spark occurs just barely after top dead center. You can tell a cylinder is coming up to the firing piston if you put a thumb over the number one spark plug hole as you slowly crank the engine. As the piston comes up with both valves closed on the compression stroke the building pressure in the cylinder will start to blow by your thumb Again get the wire back in the bore and test to see that the spark for number one cylinder occurs slightly after top dead center. This will insure that your engine will not kick back when you crank it because the spark will go off just after the piston has crossed top dead center and is starting its descent for its power stroke. When the impulse starter is no longer snapping ( after the engine starts) it will have advanced the spark firing to occur before top dead center allowing the fuel to start to burn about about 12 or more degrees before it starts to push the piston back down on the power stroke.

Now to find the rest of the firing order. Roll the engine over until you are coming up with the compression stroke on number one when the air starts to lift your thumb, stop cranking and put a wad of paper towel or tissue in each spark plug hole. Now, back to the crank! Roll the engine over and number one cylinder’s paper wad should pop out. Keep cranking and the next time you pull the crank back up towards top dead center a second wad should pop from one of the three remaining cylinders. That is number two in your firing order and that plug should be wired to the terminal just to the left ( counter clockwise) of the number one terminal. Mark that cylinder number next to the number two cylinder terminal on the back of the mag. Keep rolling the engine and the number Three cylinder will be the next to pop and then the number four will pop. Mark them respectively on the back of the mag with the pencil. You now have your firing order!

Screw in the plugs with about a .020 gap and then make up high tension (solid wire not radio noise suppression “wire” ) to connect the plugs to the magneto’s distributor in the counterclockwise order corresponding to the firing order you just discovered. Hook up the mag terminal, which should be sticking out of the side of the points case at the back of the mag and will be insulated with little fiber washers, to a switch on your dash which should be wired back to the base of the mag or some other convenient grounding point. You stop the engine by grounding the mag so it cannot create voltage in the fields that crates the spark when the mag points open.

So, there you have it!

Good luck!
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Re: Splitdorf lo and hi-tension magnetos

Postby hcca » Fri Oct 13, 2017 10:21 am

Thank you
Very informative and clear
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