Ignition Coils

[vph-d]

Does anyone know of a way to test old H-D square coils with an ohmeter? I have several -48 style coils I'd like check before installing them.
Thanks, VPH-D

[BONES47FL]

Though it is not with an ohmeter, there is a bench test for coils in Palmer's book on page 400...Bones

[vph-d]

Anyone? Anyone?
VPH-D

[Chris Haynes]

If ya can find a Duo Gap tester that is what the MoCo used.

[Perry Ruiter]

If ya can find a Duo Gap tester that is what the MoCo used.

That's a really cool picture Chris. You can see a Weidenhoff generator test bench off to the right.

Does anyone know of a way to test old H-D square coils with an ohmeter? I have several -48 style coils I'd like check before installing them.
Thanks, VPH-D

Anyone? Anyone?
VPH-D

Attached is an internal coil wiring diagram (courtesy of Uncle Frank). You can see the two external terminals are the primary winding and the two plug wires are secondary. I don't have a coil here to take readings off of, but the primary should have low resistance (< 10 ohms) and the secondary should have high resistance (> 10,000 ohms) and there should be no reading between primary and secondary. I think a coil can still be bad if it passes those readings, but it won't be good if it doesn't ... Perry

[Chris Haynes]

[QUOTE=Perry Ruiter;103729]That's a really cool picture Chris. You can see a Weidenhoff generator test bench off to the right.

The Duo Gap tester is also a Weidenhoff product. H-D used a lot of Weidenhoff stuff. Weidenhoff today is known as Sun.

[Johnny]

The values I usually read for the primary side of the coil are around 1.2 Ohms and for the secondary side are around 17,000 Ohms.
An infinite reading on either side would indicate an open circuit and values a lot lower would indicate some of the turns are shorted. Any reading within maybe 20% would indicate your coil is good.

[Perry Ruiter]

The Duo Gap tester is also a Weidenhoff product. H-D used a lot of Weidenhoff stuff. Weidenhoff today is known as Sun.

And if I understand the corporate hierarchy properly, Sun is owned by Snap-On ... Perry

[Robert Luland]

An ohms meter is just giving you nothing more than a quazy continuity test. Is there a way to load test it?

[bmh]

Energize and trigger it with the leads held off ground, should see a strong spark. They can still go thermally intermittent, but that's the best way I can think of to test them. If you have a running bike just disconnect the coil that's on it and use some jump leads to the coil you need to test but all you really need is a good battery, some wire, contact points and condenser. I've seen many 12 volt coils pass the ohm tests and still not run right.

[camsaure]

Hi, Has anyone got a copy of the instructions for the Wiedenhoff Duo Gap model 358? I just acquired one of these in very good condition. I can probably figure out how to use it, but I am sure there are some other tricks that I am not aware of. Thanks, Cam

[kenny]

Have you found information about model 358 duo gap tester I have a tester that needs restoring but no operating instructions. Any help greatly appreciated.