The Incomparable Wico EK Magneto

Closeup of the Wico

Closeup of the Wico.

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293 Four Square Drive Mount Pleasant, Michigan 48858

The following is the confession of a neophyte old engine enthusiast or, 'How my Wico Model EK magneto and I survived the first few weeks of our relationship.' After talking with fellow old engine enthusiasts, it appears I may have delved into the critter more than many. Thus, I thought I would share my experiences and information gathered during the ordeal.

When I purchased the engine it had some compression, no cracks in the cylinder or water jacket, most of the parts were on it (I suspect there is some great repository in the heavens for mufflers and gas tanks), and the magneto made sparks albeit weak yellow looking sparks. I understand from my experienced old engine friend this was a pretty good find.

My first thought was to fabricate a temporary gas tank and see if I could convert some gasoline into noise, but better judgment prevailed and I started to clean and check components thoroughly.

Alas, the magneto! Being a retired electrical engineer and one who has toyed with gas and diesel engines over the years, I felt confident the rather simple EK magneto would be operational in a few hours. Boy, was I wrong! I now know that although the EK is not a complicated device in principle, it is full of special and exacting needsor should I say mandatory requirements.

Upon opening up the magneto I found it had suffered many indignities, e.g. one breaker point was cracked, the cloth wrapping around the coil was torn and frayed, old lamp cord had been soldered to the coil primary wire ends and wrapped in an abundance of plastic tape, and a tape laden condenser was stuffed in the cavity above the coils.

The movable breaker point was not even locked in place. This should be a piece of cakere place the points, re-solder new primary leads and encase the joints in heat shrink tubing, install a new condenser, and finally coat the coils with glyptal (the red insulating varnish used by electric motor re-builders) and we should see a nice eighth inch long blue spark, right? Wrong!

I went to see my friend Mike Zingery, owner and operator of Roy's Magneto in Mt. Pleasant, Michigan. Mike repairs hundreds of magnetos, largely for oil field engines, tractors, stationary engines, and he 'does rebuild 50 to 60 Wico EKs a year.' He even has an original Wico EK magneto test machine.

Mike asked if I had checked the coils for shorted turns or open winding(s). I uttered a sheepish 'no.' Mike said 'if you can get a 7mm spark jump with a primary coil current of 1.2 amps or less, you probably have a good coil. What this means is by applying an interrupted variable DC voltage to the coil's primary windings while measuring the coil current, one can get a good idea of the coil's condition.

From the junk box I found an old set of tractor points (both sides), a small 1200 rpm electric motor which I fitted with a cam made from more gems from the junk box, a battery from my portable electric drill, a small wire wound rheostat, and a multimeter capable of measuring DC amps.

As I slowly increased the primary current, at 1.18 amps I got the much wanted 7 mm spark jumpthe coils were good. That's the good news; the bad news is that on the engine the magneto wasn't producing the kind of spark needed to make my hit & miss engine start and run well. Were the magnetos strong enough to make a good spark?

In an old engine primer I read, it stated 'Some instructions manuals say the magnets should hold a ten pound weight.' There was no indication as to whether the weight should be applied directly to the armature so as to pull the armature away from stationary poles or should the ten pound force be applied to the trip mechanism. My EK is a Type 3 magneto (Type 2 seems to be more common) relies on 'cocking' the Wico part number 186 drive spring to snap the armature and movable point away from the magnet poles. The smaller, number 97 return spring, functions to reset the armature on the magnet poles. Supporting the magneto body in a vise and hanging weights on the armature, my magneto armature supported the ten pound weight but tripped at seven pounds when the force was applied to the magneto/valve rod. It appeared that the magnets in the EK were strong enough to induce a good spark. But it didn't!

I remembered Mike saying that the armature must break away from both pole faces at the same time and they must uniformly contact each other; if not, a weak spark is the result. The tripping action is so rapid that it is difficult to visually determine if one pole is breaking the magnetic circuit before the other.

To check the armature pole faces for equal length, I removed the armature, found a reasonably snug fitting arbor to slide into the armature guide pin hole (the shank of a good 5/16 drill will suffice) and placed the arbor in a vise. Having a magneto base dial indicator (the same could be accomplished by any firm reference stop and a feeder gauge) I rotated the armature pole faces on to the dial indicator.

Sure enough one pole extended more than 0.035 of an inch further than the other. I disengaged the dial indicator and gave the shorter arm a 'calibrated rap' with a one pound ball peen hammer. Rechecking with the dial indicator showed several more 'precision adjustments' were accessory to bring the armature faces within a few thousandths of an inch of each other. My EK was still weak.

The next move was to examine the armature/stationary pole match up. After cleaning, careful examination in front of a good light, I found the poles to be touching on the back side, but a considerable gap existed on the front side. In fact, I could slide a 0.006 inch thick feeler gauge almost halfway between the poles.

The proper repair approach would probably employ a surface grinder to reface the armature poles, but I no longer have access to such. The question became, did I still have the touch to properly square these pole faces with a 'Swedish mill' (hand file) or should I try to rig up a grinding device in my drill press? Oh, go for it! I coated the pole faces with the die maker layout fluid (a magic marker will do just fine) and started to file, checking where the metal was being removed and the clearance with a feeler gauge frequently. I had to achieve a flat and square surface.

After several nervous tries, I could barely start a 0.002' feeler gauge under one corner that's good enough. A re-check of how much weight the armature would now support indicated an increase of almost eight pounds and now the magneto would give a spark almost every trip why almost every trip?

The Type 3 and the Type 1 EK magneto (the Type 2 has a different spring and mechanical finger trip arrangement) relies on the attraction of the magnet poles to the armature to allow the engine cam to compress the number 186 spring to the point when it trips, it snaps the armature from the magnet pole faces. This snapping action is mandatory for a suitable current to be induced into the primary winding.

I went looking for friction as a possible robber of the spring's stored energy and something that might slow down the armature's movement. I found the rod that activates the magneto and the exhaust valve was bent and dragging on the rocker arm. Not only did it have a bend, it had two 's' shaped kinks in it. I straightened the rod the best I could but resorted to buying a piece of  3/8 inch steel rod threading one end and hardening the end that contacts the exhaust valve rocker arm.

Now I got spark every trip, but still a weak spark. I learned as a kid while working in my uncle's auto repair garage that a yellow spark was not a 'hot' spark and what we want is a blue spark. How accurate this rule-of-thumb is I cannot attest, but it seems to apply.

I went back to Mike and had him recharge the magnets. A subsequent magnet pull test proved the magneto would now support slightly more than 30 pounds of pull weight, and most importantly, I got a 3/16 inch long (the gap on my test spark plug) blue spark every trip of the EK!

In summary, I can't say that your EK must satisfy all the criterion I forced mine to do. For example, I cannot say for certain that magnets supporting a ten pound pull test will not provide a good hot spark. My EK seemed to want a much stronger magnet. Perhaps some more experienced magneto person can improve on what I have reported. In any event, if you decide to work on your ailing EK I hope the foregoing will be of some help.