HD 25 coils

[Greg O.]

I have a nice looking HD 25 I that does not have spark. I tested the coils with an ohm meter, and the secondary windings tested open. I have not had any success finding replacement coils. Is there another coil that will fit the core of these coils. I have used OMC coils with a 7/16 center to fit the cores on an old Elgin motor. Has anyone found a replacement coil to fit the HD 25 cores, or been able to adapt a coil some way?

 

[Faztbullet]

You would be better posting over on the AOMCI site....

 

[Greg O.]

Never been there, but will check it out. Thanks.

 

[oldboat1]

coil testing can be a little uncertain too, IMO. Coil might turn out to be OK -- points/condensers could be the problem, and then maybe only a matter of cleaning and setting points.

 

[Greg O.]

coil testing can be a little uncertain too, IMO. Coil might turn out to be OK -- points/condensers could be the problem, and then maybe only a matter of cleaning and setting points.

Correct me if I am wrong, but if the secondary circuit, spark plug wire connection at the coil to ground, tests open the coil is shot.

 

[oldboat1]

If you are sure it's open. 6 or 7K ohms resistance, give or take, would be normal. Might try the tester on a different setting or two. Your call, of course.

edit. could be less.

 

[Greg O.]

I tried both settings on my cheap Walmart ohm meter, and no reading. I have used it to test other coils. I prefer a cheap analog meter for testing coils rather than a digital display meter. Thanks for the reply.

 

[oldboat1]

If magneto is assembled, might test resistance from plug boot connector to the mag plate. With your meter set to Rx1K, try for a reading. If you get nothing -- no needle movement -- would first assume a bad connection (no continuity). If you get any reading, secondary winding is probably OK. (expect continuity -- no or minimal resistance -- from boot to coil connection, but 3 to 8K ohms resistance on secondary coil winding.) My meter is a radio shack analog -- probably inferior to your Walmart version.

 

[Greg O.]

I read right from the solder joint where the spark plug wire is soldered onto the coil, to ground. Zip, Zero, Nadu.

 

[oldboat1]

well, is what it is. could try your meter test on a known good coil to benchmark. also, might try resoldering the connection, then retesting. But AOMCI is a good source. Good luck -- good project motor.

 

[Greg O.]

Thanks Oldboat1

 

[HighTrim]

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 lead exit. On the BOTTOM of the coil, the shortest and longest leads exit the coil.

To test the secondary circuit, you place your probes on the shortest 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 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.

 

[F_R]

Greg, I suppose by now your have read my post on your aomci thread, concerning Maverick Spark Suppressors. Forget everything else till you determine whether or not those are an issue in your case.

Whatever, those coils were made before OMC discovered how to make coils that fail after two years (so to speak). But they are nearly bulletproof and failed ones are fairly rare. I don't advise replacing them till you have for-sure determined they are bad.

 

[Greg O.]

FR, there is no continuity between the spark plug solder terminal, and the ground terminal below that. There is continuity between the two longer wires (primary circuit) . So I am to assume the coil is bad. I would condemn any other coil that is open. So unless I am missing something I believe this coil to be bad. I am going to recheck the one still on the magneto. Thanks again for the help.

 

[nabiul]

I remember there was something weird with the coils when I was fixing my HD25; one of my circuits was reading open and eventually the wire came off as I was moving it around. The coil casing had a grommet installed, but the actual wire didn't come out of the grommet but rather a small hole in the circular gap in the outer casing. The wire was then bent towards the grommet and then bridged to it with solder which made a weak connection.

This may be what is happening to you, it might be worth desoldering the wires and taking a look at whats under the blob.

 

[F_R]

FR, there is no continuity between the spark plug solder terminal, and the ground terminal below that. There is continuity between the two longer wires (primary circuit) . So I am to assume the coil is bad. I would condemn any other coil that is open. So unless I am missing something I believe this coil to be bad. I am going to recheck the one still on the magneto. Thanks again for the help.

Your test confirms a bad coil (open secondary). I'm quite sure you know enough to have your meter set on a suitable scale to read a few k-ohms, right?

 

[HighTrim]

^^^ Very good point!

I have seen that before. Guys brought over their "junk" coils, however the only problem was the meter, not the coil. Or, lack of the proper setting/scale

 

[Greg O.]

Defiantly on the correct setting. Checked it with a new coil, all was good. Thanks.

 

[Woodsmanwill]

Anyone know what size replacement spark plug wire is needed for a HD-25?
SN: 93823

 

[racerone]

Just 7 mm with wire core.-----Not hard to find.