Topic: What exactly does The small coil do? – Antique Outboard Motor Club,Inc

This topic has 16 replies, 7 voices, and was last updated 9 years, 5 months ago by legendre.

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June 17, 2015 at 12:13 am #1771
benchrascal
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I’m working on one of these 1974 Johnson 9.9hp and as per usual I’m having an intermittent ignition problem.I don’t think I’ve ever owned one of these without an ignition problem actually ,anyway the points are clean and set to 020 ,the coils are both decent as are the condensers ,everything looks really clean and tiddly with the possible exception of the little coil under the flywheel .I don’t understand it’s purpose or if would cause my problem.Is that a possibility?
June 17, 2015 at 12:49 am #18235
willg
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US Member
That would be the driver coil. Fleetwin or T2Stroke will probably chime in later to explain its purpose.
June 17, 2015 at 3:38 pm #18274
orpilot
Participant
That is the driver coil. As I recall it outputs about 200 volts depending on the model that it sends to the primary circuit of the ignition coils. The igniton coils then boost it to 15 to 20,000 volts. It’s basically the precursor to CD igniton systems, one of several "innovations" OMC came up with to keep their early 9.9 and 15’s from fouling plugs at trolling speeds. Having worked as an OMC tech during that period I can tell you the ’74 to ’76 models were generally a pain in the keister. It wasn’t till the CD ignition came out in ’77 that the problems were fully resolved.

As to your intermittent ignition problems, short of bench testing the ignition coils, the first thing you can do is check for continuity of the secondary circuit of the ignition coils – one lead to ground and one lead to spark plug terminal. If it doesn’t show a circuit there, try moving the plug terminal around to see if that’s the culprit. My experience was that the driver coils didn’t fail that often. The other problem common with those models was loose armature plate bushings that allow the points to wander around in their setting which of course effects ignition timing, usally showing up as a rough idle.
June 17, 2015 at 5:03 pm #18277
fleetwin
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US Member - 2 Years
Yep, that driver coil is a simple winding, pretty rugged unless physically damaged by rubbing on the flywheel magnets. But, OMC did "improve" the driver coil in later years for better ignition performance. There was recently a thread about driver coil resistance, but I can not remember the exact spec, differs between manual start and electric start models. I believe the resistance is very low, only a few ohms. You can also check for shorts to ground using the high ohms scale with the driver coil leads removed from the point terminals, you should see an infinite ohm reading when connecting one ohm meter lead to the mag plate, and the other lead connected to either driver coil lead.
Check simple things first, like the ground strap between the mag plate and engine block. Calibrate your ohm meter to the low ohms scale, connect one lead to a good engine block ground, the other to a good mag plate ground. You should see a reading as close to zero as possible. Rotate the mag plate while checking the resistance also, to ensure the ground connection is not intermittent. You could also disconnect the stop switch lead connectors to rule out a faulty stop switch/wiring/circuit. Sometimes the mag plate wiring harness gets shorted or chafed causing a problem as well. And, like Orpilot says, the wobbly mag plates were a big problem.
We all were thrilled in 1977 when the magCD system was introduced on the smaller engines!
June 17, 2015 at 5:24 pm #18279
legendre
Participant
Is this the system in question?

This system has three coils on the stator; would the driver coil be the one shown on the right?

One question that immediately comes to mind, is "If they’re going to have an alternator and a storage battery, why on earth didn’t they implement a standard battery & coil ignition?"
June 17, 2015 at 6:01 pm #18282
fleetwin
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US Member - 2 Years
Yes, the single coil on the right of the picture is the driver coil on the electric start/alternator wiring diagram you posted.
While there is an alternator, it is only capable of about 4-5amps at WOT, I doubt it could keep up with the load presented by a conventional battery/coil ignition system. Additionally, you would have to have some sort of mag system for manual start models. Like we say, most of these ignition/plug fouling woes disappeared in 1977 when the magCD system was introduced on the smaller outboards. No points, a pretty simple "plug and play" system.
June 17, 2015 at 6:51 pm #18284
benchrascal
Participant
Turns out there is nothing wrong with any of the components .it’s the operator needs a tuneup .After switching out and testing everything I stood looking at the motor and for some reason decided to (finally) check the top end for bearing runout ,…. well turns out there is so much wear that the point setting is a suggestion only ,once running it picks one cylinder and stays there.Funny thing because this motor is so clean i would never have suspected such extreme wear.Oh well can’t win them all.
June 17, 2015 at 7:39 pm #18287
johnyrude200
Participant
When you say bearing runout, what are you talking about? Wobble at the crank due to worn bearings? I recently acquired a couple of 18-20-25 powerheads from a closed marina and noticed excessive play in the crank. This winter I’ll split the crankcase and see if there is a broken crank or worn out bearing in either of them (pretty sure one is broken, and the other is worn).
June 17, 2015 at 11:04 pm #18303
fleetwin
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US Member - 2 Years
quote johnyrude200:

When you say bearing runout, what are you talking about? Wobble at the crank due to worn bearings? I recently acquired a couple of 18-20-25 powerheads from a closed marina and noticed excessive play in the crank. This winter I’ll split the crankcase and see if there is a broken crank or worn out bearing in either of them (pretty sure one is broken, and the other is worn).

Unfortunately, sloppy upper bearing/crankshafts were not uncommon for these engines. And, unfortunately, they came from the factory this way. I’m guessing OMC let the tolerances slip on these parts. I just don’t want you pulling the powerheads apart only to find nothing really "wrong". I guess what I’m saying is don’t bother to pull these things apart unless the slop is really excessive and obvious wear due to rust is found.
June 17, 2015 at 11:07 pm #18304
fleetwin
Participant
US Member - 2 Years
quote benchrascal:

Turns out there is nothing wrong with any of the components .it’s the operator needs a tuneup .After switching out and testing everything I stood looking at the motor and for some reason decided to (finally) check the top end for bearing runout ,…. well turns out there is so much wear that the point setting is a suggestion only ,once running it picks one cylinder and stays there.Funny thing because this motor is so clean i would never have suspected such extreme wear.Oh well can’t win them all.

Are you sure the upper bearing/crank is worn? The usual problem is wear between the crankcase pilot bushing and the mag plate bushing. These engines aren’t known for upper bearing issues, unless rust or mechanical damage is obvious.
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