Ignition coil

[otis71]

Lost spark on my rear cylinder on an oem 6v metal coil. If one cylinder is firing, is the coil good? I replaced the end on the spark plug end and the lead looks good. I didn’t want to melt it out until I’m sure the coil isn’t bad.

[otis71]

Also I checked the coil with an ohm meter and it read 1.5.

[Lyle Manheimer]

Otis,
An ohm meter test can be inconclusive. You are testing the primary winding of the coil and it is reading ok. Many times when an ignition coil heats up the primary winding will fail open. When the coil cools it often reconnects the winding and the coil will work again for a few miles. This would affect both spark plugs.
You have a problem with only the rear plug loosing fire. The probable culprit being an insulation failure from the primary side of the coil, low voltage, to the secondary side of the coil, high voltage side. This will probably not show up with an ohm meter.
Long story short, it is likely to be a faulty ignition coil or a failed plug wire. Make sure you check the plug wire before changing the coil.

[otis71]

I pulled out the plug wire. It has continuity and looked to be ok. I reinserted it but still nothing. What does the plug wire connect to in the coil? I’m assuming there is a spike but can’t get a visual on it.

[bobphd]

There is a spike and it is difficult to see. I have found several coils that I thought were bad but the problem was broken plug wire inside the coil. I use a piece of outer throttle or brake cable with the jacket removed and attached to a drill to clean out the passage way to the spike. Bob image.jpg

[bobphd]

You also need to check continuity between the plug wires when installed in the coil as that is the secondary windings. I don’t recall the resistance in ohms but it all aint much. Bob b

[otis71]

I felt in there with a small screwdriver and the spike is there. Something is loosing continuity but it’s not the plug wire. I had a brand new aftermarket coil so I put on for now. The plug wires were too short from the vendor. The bracket was riveted to the coil too low so the top mounting hole was halfway behind the coil. The rivets holding the bracket were loose. The spark didn’t seem as hot as the oem coil but the bike is running now. Can the oem coils be repaired?

[Peter Cooke]

Can the oem coils be repaired?

Here's how I did it. I'm sure there are lots of other ways though.

Coil Upgrade - AMCA Forum (antiquemotorcycle.org)

[pan620]

This guy makes very nice reproductions bulldogbrothersgarage@gmail.com

[otis71]

I also have a JD that I’m running a -30 VL coil. A fuel leak made all the tar run out. What can I use to replace it?

[Rubone]

I also have a JD that I’m running a -30 VL coil. A fuel leak made all the tar run out. What can I use to replace it?

If enough gas got in to melt the tar it could have also melted the shellac insulation on the wires rendering the coil useless. Have you tested the coil? Specs are in the service manuals.

[otis71]

Due to non stock application, the coil was mounted horizontally and damage was left just to the tar. I replaced the wires and ran it just yesterday. The packing washers alone make a nice seal.

[otis71]

The V Twin coil I installed lasted all of about 5 hours riding time so I’m going to retrofit an old coil. The coil suggested comes from overseas and I’m a little impatient. I fought a coil I can get in a week. It is 1.09 ohms primary resistance and 13-14 ohms secondary. Is this adequate?