MTFCA Forum

A friend has a dilemma about his T and asked me if I could shed any information. I suggested to clean the MAG post but I am not sure if this is the remedy. His engine starts on BAT but not on MAG. The engine runs smoothly on BAT but rough on MAG. The T is a '22. Any and all input is appreciated.

Until this test is performed: http://www.mtfca.com/discus/messages/70 ... 760271.pdf and the results are published, every suggestion you receive will be pure speculation and guesses.

Now you have something to do and it only took 6 minutes from your question to having a task to perform.

Scott, excellent advice, just one further comment to it...

The meter used, called an analog meter by the write up is the meter with the sweep needle, not the one with the 7 segment LED as shown in the write up...

I've actually had success over the years with a digital in most cases when that was the only type available when I would be helping someone out. One time I do recall having an electronic one that rang so loud with' 'noise' it was absolutely worthless to use as a troubleshooter on a T.

Each one of my T's has a cheap analog volt meter in it. You can usually pick them up really cheap at the 'up front' racks at Harbor Freight, Pep Boys, or Autozone. The cheap ones are good enough for magneto checking and make great continuity sensors...

I've also built small project boxes according to the diagram with 'poke' contacts for the meter leads. Will have to see if I can find some pics for further posting...as you point out, simple enough even to breadboard together...

To Original Poster
The Model T Ford ignition system is compromised of sub-systems and each subsystem must be in proper order for the system to work properly. Conducting the test recommended by Scott Conger will help isolate the problem and give insight as to where to be looking. Conduct the test exactly as indicated and have someone who understands how to interpret the test results data. A more comprehensive test would be to check the magneto with a St Louis mag tester. This device takes all the guesswork out of interpreting the voltmeter test results.
There is one passage (second to last sentence) in your post that caught my attention; "running ok on battery and rough on magneto" is the classic symptom of improperly adjusted ignition coils. If you can locate a set of known properly working coils and try them it will also help isolate the trouble.
Remember the other subsystems; timer, wiring coilbox and proper initial timing setting.

I first read this as 'A friend has DEMENTIA about his model t.

Me too brother, me too.

6. possible causes:
1. bad connection at switch
2. poor connection at the magneto plug
3. Magnetic field in magnets is weak meaning magnets need to be re-charged
4. Space between the magnets and coils too large, due to wear on the third main bearing thrust surface.
5. Magneto coil ring is grounded near somewhere in the middle of the ring so only some coils working
6. Ignition coils not adjusted correctly for use on magneto.
Norm

To check the connection at the switch, remove the wire from the magneto plug and connect it to the battery. Then try turning the switch to magneto. It should run the same as it does when the switch is turned to battery. If not, check the switch.
If that does not disclose the problem, next thing would be to measure the magneto output. This is done with the engine running on battery. Connect a 12 volt bulb between the magneto post and ground. Then with the engine running on battery, use an AC voltmeter across the light bulb. You should have at least 6 volts AC at idle with a steady increase to around 25 or higher volts AC at high speed. After you make the test, put the wire back on the magneto plug.
If this test is good, I would suspect the magneto is working and the plug connection is good. If the test is low, then remove the plug and check for lint or other debris around the plug. Make sure the plug is making good contact with the button at the top of the magneto ring. Another thing to test if mag output is low is to jack up the rear wheels and put the parking brake on with the engine running. Leave it in that position but turn off the key. That would push the flywheel back away from the coil ring. Now go to the front and gently pry between the crankcase pulley and the front of the engine. If there is a noticeable movement forward when you do this, your endplay is too great. This must be fixed by adding to the thrust surface at the front side of the rear main cap or repouring the cap.
To recharge the magnets you will need to at least remove the hogs head and use a magnet recharger to charge them. If this needs to be done, I would recommend you ask your local club to recommend someone in your area with experience in how to do this. Instructions are found in the booklet published by the national club,"Electrical System".
If the measurement of the output is good, the next thing would be to check the ignition coils. They should fire at 1.5 amps and all give a good strong spark.
Note, it is normal when running on battery, for the spark to advance in a steady curve as you move the spark lever down from full retard to full advance. But when you run on magneto, you will find about 3 or sometimes 4 positions where the spark will advance suddenly as you advance the lever. That is it will move a few notches without a noticeable change and then one more notch and it will suddenly advance. Then a few notches with no advance and then as you move it it will suddenly advance. This is normal, however if the coils are not adjusted the same for each coil, you might get some overlapping at that point where the spark will suddenly advance because it might advance with some coils and the others are not charging up enough before the current reverses due to the AC output.
Anyway, that's about all I can think of which might be causing your problem. You should do the tests first and try to determine the cause before you start tearing things apart.
Norm

Unless the magnets are so weak so as not to get a N/S reading when checking, there is no need to remove the hogs head for in car recharge. Checking output and end play are good places to start. As Ron suggest, also checking the coils, they could be miss adjusted. Have the coils been rebuilt and/or adjusted?

To all of you who replied...Thank You for your advice. I've printed your responses and gave the copy to my friend. Hopefully he will be successful in fixing the dilemma.