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Replacement coil for CCK


Hello, first post here and hopefully in the right forum. A few years ago I purchased an old Gravely tractor for the purpose of rebuilding its Onan CCK to use to power a 10hp air compressor I had. I built the rig on a utility trailer so it could be pulled out in a field (or wherever) for sandblasting or anything else that I needed air for that wasn't close to my shop. It has worked beautifully until recently when it quit on me. I have a bad coil (secondary coil is open) and really don't want to pay for a new one.

I've read about using a coil from a motorcycle and happen to have one. I have a copy of a manual but it really doesn't give any specifics about the coil and I have some concerns about resistance across the primary of the motorcycle coil as well as if a ballast resistor should be used to drop voltage/amperage at the points for longevity reasons. If it helps, the original coil is #166c346 and the Harley coil I have measures 2.5 across the primary coil.

Can someone point me in the right direction? Thanks.

Elden DuRand

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I don't see why a Harley coil won't work. First, though, are you sure the Onan coil is bad.

Unlike single cylinder coils, the way these coils are made, they will show an open circuit from either tower to ground but will show a circuit between the towers.

Since both plugs can fire at the same time, "wasting" a spark on each cylinder, one end of the coil secondary winding goes to one plug. The current flows across that plug gap, through the engine frame, across the other plug gap and then goes to the other end of the secondary winding.

You can hook the Harley coil up the same way as the Onan was connected but first, check the primary resistance. If it is the same as the Onan, you're good to go. If it is about half the resistance of the Onan, you need to get a ballast resistor from something like a '57 Chevy to put in series with the primary.

Hope this helps.

Take care - Elden:wave:


Thanks Elden. I do have an open circuit between towers. I was just concerned about having too much current at the points and burning them out in short order. I'll try it out this weekend. Thanks again.