Johnson HD 25 coils

[greg-o]

Hello everyone. I am new here and probably will spend some time here, as well as join the AOMCI. I have a meager collection of about 50 motors, some running, some for parts, some future projects.

Anyway I have a very nice Johnson HD 25 with no spark. I tested the coils with an ohm meter,between the solder joint for the plug wire, and ground, and it appears the secondary windings are open. Am I to quick to condemn these coils? Seems to me the secondary needs to be a complete circuit.

I have not been successful at finding coils yet. My question is… Has anyone ever found a coil that will fit the core of the HD 25 coils? I have done this before with Elgin coils. The coils off the newer OMCs 50s, 60s and 70s, will fit the Elgin cores. The core size of the HD25 is approximately 5/16. The other option I guess is used coils.

Another question regarding the same coil. On the bottom side of the coil is a small cylinder shaped object secured to the armature plate with a screw. It looks like a small condenser. What is it? I managed to break it off one of the coils, as I didn’t look close enough to see it there, and it twisted right off as I was removing the coil. As I said, the coil tested no good anyway with the ohm meter.

Thanks for sharing your knowledge. I look forward to reading through this forum.

[Mumbles]

Here’s some HD coils I tested a while back and the good ones were giving a secondary reading of under 4K ohms.

With the small core size, I think you’d have to make up some shims if you tried adapting an OMC coil to the HD lams. I’ve never tried it but it might work.

Can you post a pic of the round thing under the coil?

[frankr]

Early HD models had "Maverick Spark Suppressors". That may be what you are looking at. If it is, there is no continuity through those. The spark current jumps the internal gap as it returns to the coil. However, I don’t think that applies to the HD-25. I would have to do some research to figure that out. Or, the mag may have been swapped from an older model. A side note, the suppressor-equipped models used a different magnet rotor also. Bottom line, check the continuity between the solder joint and the secondary winding’s ground lead. That eliminates the suppressors if they are present.

BTW, Maverick Sparks are extra stray sparks that occurred on early models. The suppressors do exactly that–suppress those stray sparks.

[chris-p]

I saw your post on the other forum, but will copy what I found here.

Those coils rarely fail, however, it does happen.

There are 4 test "points" on the 375189 coil as you know. On the TOP of the coil, the spark plug lead and a medium length(ground) lead exit. On the BOTTOM of the coil, the shortest(ground) and longest leads exit the coil.

To test the secondary circuit, you place your probes on the shortest ground lead on the BOTTOM of the coil, and the spark plug lead on the TOP of the coil. I find that the readings of these 375189 coils is not as "high" as you would find on an OMC Universal Coil. They seem to be in the mid 3000 ohms resistance, usually about 3600 on the x100 scale on your analog meter. If the coil has failed, this is usually where.

To test the primary circuit, put your leads between the other two leads on the coil, that is the longest ground lead off the BOTTOM of the coil, and the medium length lead, off the TOP of the coil. Here, you will find your analog meter should swing way over to the right, to zero ohms resistance.

EDIT: For those of you with Mercotronic Tester, the operating amperage of this coil is 1.5, the primary resistance is .375 to .575, and the secondary continuity is 30 to 45 as per my manual.

I have a NOS coils I just pulled out to test out of the box. Sparked up o the Mercotronic! Maybe a member in your area has a tester they can check your coil for you. Im a little far away, but would be glad to if you wanted to mail it to me.

[frankr]

image hosting over 10mb

screen shot on pc

[Mumbles]

I’ve noticed that some of these coils have either three or four wires coming out of them including the hi tension lead. On the four wire coils, two of them must be separate grounds for the primary and secondary windings inside them.

[frankr]

Exactly. The four wire ones were holdovers from the Spark Suppressor days, which required a separately-grounded secondary winding. In post-suppressor days, the secondary wire was simply grounded.

[chris-p]

When I test the 4 lead units on my Mercotronic, I just run a jumper lead between the grounds to the ground lead off the Mercotronic.

[greg-o]

I went back a re tested the one coil I took off, between the spark plug wire terminal, and the bottom ground right below with the short wire. It is definitely open.

But here is where the plot thickens. I was looking more close at this motor, and my understanding it is a HD 25. However it has HD20 stamped on the block. Also one of the owners, I assumed it to be the original owner, inscribed his name and date on the motor, which I think is really cool.

http://i1382.photobucket.com/albums/ah2 … kw6y4v.jpg

http://i1382.photobucket.com/albums/ah2 … bkublx.jpg

http://i1382.photobucket.com/albums/ah2 … ylvtkx.jpg

[greg-o]

Can I post pictures directly or do I need to be a member to do that?

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