TD-20 Coils?

[starcraftkid]

I just came across two older Johnson motors, one a TD-20, the othe is a TS-20.
Both have strong compression and are complete minus the lower skirting on the TS-20.

Both need coils, both have spark on the first pull or two on one cylinder the its gone. The points are clean and making good contact and are gapped cat .020".

Both were part of a package deal for a few other newer motors. I really don't have a use for them but figured it would be neat to get the up and running. The TD started for a second or two once but lost spark after that.

Is there a source for new coils? The original coils on both are black plastic or epoxy, neither shows any signs of cracking but both top coils have a tan sticky goo oozing out. Both were stored in an old shed for over 50 years.

 

[oldboat1]

Re: TD-20 Coils?

'40s motors, I think. Interesting find. If you are just messin' around, grab a coil from one of your other motors (maybe the TS coil for the TD) and make a switch. Try for spark. But you are right -- need to replace the old coils with new ones, if serious rebuild, cracked/leaking or not. I use NAPA as a source for my '50s motors if aftermarket works for you.

 

[JRegier]

Re: TD-20 Coils?

Unfortunately I believe those are before the universal ignition. Horseshoe coils that are hard to come by. I've read that the coils hardly went bad but they used a magnet separate from the flywheel for the ignition and it could demagnetize over time.

 

[nwcove]

Re: TD-20 Coils?

You may be able to use the windings from universal coils on the original cores.

 

[oldboat1]

Re: TD-20 Coils?

oops. sorry Starcraft. But maybe you can do some switching with what you have to get one of the motors running, anyway.

 

[HighTrim]

Re: TD-20 Coils?

Yeah NAPA wont have those coils

At nwcove stated, you can pull a Universal Coil off its lamination, then transplant it onto the original lamination, with minor surgery. Or try to locate some good sparking ones. I have a couple on a motor, but unfortunately just sold them. A wanted ad at aomci.org in the webvertize section should get you something. Or try Doug Penn. Google his name and his website will come up.

 

[Sarentack]

Re: TD-20 Coils?

You never know about Napa, they have everything but Car parts.

 

[F_R]

Re: TD-20 Coils?

I have found those old center magnet coils rarely go bad. That goo leaking out is beeswax. Supposedly not a good sign, but the coils don't know it and keep on working anyway.

 

[oldboat1]

Re: TD-20 Coils?

ah, so maybe the spark issue is a bad wire or connection at the plug, something that can be corrected. Starcraftkid, I would like to see a pic of the magneto if you get around to it -- curious.

 

[starcraftkid]

Re: TD-20 Coils?

I was actually surprised to find that the coils were plastic. The magnets in the center seem pretty strong but not as strong as a newer flywheel type magnet. The bottom cylinder fires intermittently, I'm not convinced whether its due to a coil giving out or some something else. The wires all read 0 ohms, the points close and read 0 ohms, and I've swapped around the condensers and disconnected the ground out wires and still I get only very weak spark on the top cylinder and intermittent spark on the lower cylinder.
It looks like someone has re-soldered all the connections on the coils, the coil for the top cylinder which was leaking wax was all fuzzy looking around the plug wire connection.
The coils on the TS 20 are dead, I get no spark at all from that one no matter what.

Is there a way to test these coils with an ohmmeter?

 

[HighTrim]

Re: TD-20 Coils?

You can test the primary and secondary for continuity, however the ohmmeter will not put a "load" on them for proper testing. Most issues are in the secondary winding. It is long, and thin, compared to the primary which is short and fat. If the secondary is fractured, an ohmmeter may not pick up a problem with it. Needs the Mercotronic or Stevens tester for that.

However, if there is a total failure in the windings, the ohmmeter will tell you that.

You should bury the needle on the primary winding, and get about 3000 to 8000 ohms on the secondary winding on the 100k scale.

Actually, read this. Better with pics.

Testing an Outboard Coil with a Multimeter using an ignition coil from the Johnson H or T

 

[F_R]

Re: TD-20 Coils?

Resistance of the primary winding should be very low, around an ohm or so. Secondary should be several k-ohms.

My experience on those motors have been that 90% of the problems are dirty points. Remove them from the motor, take them apart and clean and degrease everything. Polish the contacts shiny bright with some 400 grit wet-or-dry sandpaper, reassemble and set gap at .020" at widest opening. Do one set at a time so you have a sample of how they go together and don't lose any of the little insulators. Condensers may have a bunch of leakage also.

I don't recall ever seeing a weak magnet on a post-WWII motor. There was an engineering change on the magnets at some point in time around then. I don't remember when it was without researching it. Suffice to say be wary of interchanging them.

 

[oldboat1]

Re: TD-20 Coils?

Just looking over shoulders, here. Can more modern condensers be used as replacements? The ones pictured are big rascals, and physical fit for replacements would presumably be no problem. (pics appreciated, starcraft.)

 

[HighTrim]

Re: TD-20 Coils?

Yes of course. As Frank stated, they could be leaking as well. Looks like the original condensors.

For testing.

Outboard Condenser Testing

 

[oldboat1]

Re: TD-20 Coils?

a condenser is a condenser, then? no functional difference between years/models, etc.?

 

[oldboat1]

Re: TD-20 Coils?

no -- really. Can I interchange condensers between models and years, as long as they fit under the flywheel? How about OMC to Chrysler, or the other way around?

 

[nwcove]

Re: TD-20 Coils?

you can go down to the local radio shack and buy condensers, as long as they are the equivelent mf value, they will do the job.

 

[HighTrim]

Re: TD-20 Coils?

Yeah, they can swap, as long as the mfd is the same as stated above. here are some tables to help with cross reference with OMC.

 

[oldboat1]

Re: TD-20 Coils?

OK. thanks. have to determine the mf value/rating of the existing and replacement condensers. crosswalk between models is particularly useful for my stuff. don't have to get too deep in the weeds.

 

[F_R]

Re: TD-20 Coils?

The condensers used in that motor are 300153, which are .2mfd, a pretty common value. Another consideration has to be mounting style. Also, I recently got into a discussion which led me to investigate the voltage rating that is required. I was wrong in my thinking that 100V was enough. It isn't. I was really surprised to find that at least 400V is required. And there is some more, highly technical stuff to consider. Suffice to say that just any old Radio Shack condenser is not good enough. You need .2mfd, rated at 400V or more. That is entirely possible, but not real common in the Shack.