John Deere Magneto Repair

By Staff

If you are tired of paying more to have someone fix your engine’s magneto than the entire engine itself cost, then you should consider repairing the magneto yourself. Many of the John Deere Type E engines in original condition have magnetos that fail to produce a spark. In some cases if they do have a spark, it is too weak to allow the engine to run. Usually, a good thorough cleaning of all the parts will be enough to bring back a good spark to the magneto. If most of the major parts are not cracked or damaged, anybody with a few tools can disassemble the magneto, clean it, reassemble it, and 90 percent of the time it will work. After the magneto has been removed from the engine, the first thing to do is gather all of the necessary materials.

There are only a few things needed: a screwdriver, pliers, an adjustable or open end wrench, and a scraper along with WD-40, clear, black, and aluminum spray paint, and some light oil. Two of the most important things are rags and a parts can.

After these materials are gathered, you can begin work. First wipe off as much of the dirt in the magneto as possible and spray all screws and nuts with WD-40. Next, remove the wire from the magneto by loosening the screw where it is attached. Then try unscrewing the large, round black plug the wire was connected to. If it does not come off by hand, carefully use pliers to unscrew it. After you pull this out, slightly stretch the spring and clean the black pick-up at the bottom.

Now unscrew the two screws on each side of the center strap that holds the horseshoe magnet in place and remove the strap. Firmly hold the base and try to pull off the magnet. If it does not come, lightly tap it with a rubber hammer (do not use metal because if you hit it too hard, you could reduce the power of the magnet). Then mark which direction it came off. Next, grab the gear firmly with your hand, use a wrench to remove the nut from the shaft, then pull off the gear. Be careful not to misplace any of the pieces. Now you have all of the external parts removed. The next step is to take apart the inside.

First, remove the four screws that hold the cap on. Slowly pry the cap off with a screwdriver, being careful not to damage the gasket. After the cap is off, slowly pull out the armature. (Make sure you have removed the black plug that the wire hooks up to as explained above because if you do not, you will break the armature.) Once the armature is out, use a rag to wipe it off, inspect it for damage and set it aside. Now everything is apart and each piece is ready to be cleaned.

Generally, everything except the armature and the black plug that takes the spark from the armature can be cleaned. Scrub everything else with soap and hot water until all dirt is gone. Next, wipe the individual parts dry with a rag and set them on some newspaper to air dry. After all the parts are dry, you can paint them if you want the magneto to look like new. Either clear or aluminum paint can be used on the base,- and black paint on the magnet. Spray paint usually works best because it goes on smoother and dries quicker. After the paint has had enough time to dry, you can begin reassembling the magneto.

Reassembling the magneto is not more difficult than taking it apart, only you reverse the order. First, slide the armature back into the base. Next, carefully slide the cover back on, making sure the gasket stays in place. Then put the four screws back in and tighten them up. Check to see if the armature turns freely. If it does not, loosen the screws slightly or put in a thicker gasket. Now all of the internal parts are back in place, the outside parts are next.

It does not matter in which order the gear and the magnet are put back on, but I like to put the gear on first so I can compare the spinning motion of the free armature to that of the one under magnetic influence. Simply slide the gear back onto the shaft and tighten up the nut as much as you can with the wrench. Spin it with your fingers to make sure it turns freely. Now, slide the magnet back onto the base in the same direction that it came off. Place the strap over it, put the four screws back in, and tighten them back up. Now try turning the armature freely. It should be much more difficult to turn now that it is under the magnet’s influence.

Now, carefully place the black plug back where it came from, screw it in tightly with for fingers, and put the wire back on to it. If you have painted the magneto so it looks like new, you should also get a new wire. Yellow wires look the best with this type of magneto. The restoration process is complete and testing can now proceed.

The magneto should be tested before it is remounted on the engine. This test is very simple and can be done in a few seconds. Hold the wire by the insulation and place the end within l/16th of an inch of a clean, unpainted steel area of the magneto (the inner side of the gear works well). Then with your other hand, spin the gear as quickly as you can. You should see a bluish-colored spark. If you do not, try it again on a different area of the magneto. The next test should be done on the engine. After you have restored the engine, try the magneto on it to see if it runs. If it does, great. If it does not, check to make sure all of the ignition parts on the engine are operating correctly.

This process may sound complicated, but it is extremely simple and if you are hesitant about attempting it, just do it slowly. You can turn a useless magneto into a very valuable one with little cost to you.

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