Doesn't run on magneto

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2010: Doesn't run on magneto
Top of pagePrevious messageNext messageBottom of page Link to this message  By Rodney A. Marcom on Sunday, May 09, 2010 - 11:32 am:

Hi all,
Just had my 1915 T engine rebuilt and am in the process of fine-tuning, resetting clutch, brakes etc. Pull-started this morning and she started right up, ran perfectly on battery power, however, when switching to magneto, she started chugging and sputtering as if not running but on three cylinders. I have done the following already:
1. Coil box taken off car, all contacts and wires checked and cleaned, no bad solder noted.
2. Checked all coils on a coil tester - good buzz and swapped all coils around in the box as well
3. Checked all contacts, wiring etc.
4. Magnets and ring were checked at rebuild and were in good shape

Where do I start next for troubleshooting this problem?
Thanks in advance.

Rod Marcom


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Sunday, May 09, 2010 - 12:07 pm:

Rod:

Most of the time a set of coils is the problem when a T runs better on battery than on magneto. This only assumes the magneto is strong enough to run coils. A buzz box type tester is often the problem in that it fools us into thinking that the coils are "OK". The coils probably have good windings and perhaps the points are OK too but the T has a unique system in that it needs just a wee bit more than that. The coils just really need to be setup on a Hand Cranked Coil Tester (HCCCT) or its equal. Perhaps someone near you could setup your coils for you with such a tester. Too often people give up on coils simply because they have never had them adjusted right even once.

If you have an analog voltmeter with a scale on it to be able to read up to about 40 Volts AC then you can connect it to the magneto post while you run on battery and measure the AC voltage at idle, mid RPM and high RPM and post those results here and we can tell you whether your magneto might be part of the problem. To make an accurate measure you will need to properly load the magneto or you might get fooled. That can be done easily by purchasing a #1156 modern 12V bulb at your local car parts store. Get a socket for it too if you can. Connect that bulb from magneto post connection to ground and thus in the same connection points as the meter. A good magneto should light it up really bright and even perhaps burn it out at high RPM. If you understand what I am explaining then give it a go and post your results.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson on Sunday, May 09, 2010 - 01:53 pm:

Rod
Here is a diagram of the test setup for magneto checking John mentioned above.
1


Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael Deichmann on Sunday, May 09, 2010 - 03:31 pm:

What about using a 24V bulb?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson on Sunday, May 09, 2010 - 04:22 pm:

Michael
The 1156 bulb was selected because it closely simulates the load of the Model T coils when the engine is running.
Ron the Coilman


Top of pagePrevious messageNext messageBottom of page Link to this message  By John H on Sunday, May 09, 2010 - 07:41 pm:

There was a magneto tester, made by KR Wilson I think, which appears to be just a moving iron ammeter. According to its scale, the magneto should put out about 4A when cranking by the electric starter and about 10A at normal engine speed. This would surely be a more demanding test than using a light bulb that draws less than 2A. True, the coils don't need 10A but you'd know if the magneto was up to factory spec.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary London on Sunday, May 09, 2010 - 07:51 pm:

Fun Projects has got an awesome magneto tester!!!! I just received one for a birthday present; it's great!!

Remember, Father's Day is coming up!! To heck with a tie, get your wives to order you a Magneto Tester!!!!! You'll be glad you did!!

And seriously, the first time you use it and prove your mag is good, and you know you don't have to rip it out to test it or set it up, you'll be thanking the wife...... I did!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By John F. Regan on Sunday, May 09, 2010 - 09:47 pm:

John H:

The Ford numbers that you speak of as factory spec are not factory specs but some measured amounts that have been restated again and again with each publication copying someone else or copying Ford's original numbers. They are measurements taken on a magneto at the Factory but no limits or variance amounts are stated. The voltage measurements were measured at open circuit but the current values shown (in amps) were with the output short circuited and thus really somewhat meaningless. The values also are shown with various RPM of the engine and AC frequency of the magneto at a given RPM but there is an error in the table which is why I know that everyone else is simply publishing the same numbers from Ford because the error is repeated by everyone else too and the published numbers are always the same identical values that Ford measured. So far as I have been able to determine, Ford never once published any "minimum" numbers that a good magneto should produce. They only published some "typical" numbers which are what we today would simply refer to as "parking lot" measurements.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gene Nelson on Sunday, May 09, 2010 - 10:41 pm:

Rod,
An oil change may fix your mag problem. It worked for me!
Gene


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Kuehn on Monday, May 10, 2010 - 09:38 am:

Check the mag post contact spring for good contact to the lead button on the mag ring.
I had a mag coil rebuilt by one of the best. When I got the engine together I looked down into the mag post hole on top of the cover and noticed that the lead button was off center to the hole!
I had to bend the spring on the mag post to have good contact on the lead button. It has since slipped off the button a couple of times but after a little modifacation it works fine now.
When I first put everything together the first time I disregared the poor contact it was making. After running it on mag it just would not run like it should. I checked everything and the mag post I checked last. Sure enough I had forgotten about the lead contact being off center. That was the problem and bending the spring to have better contact was the answer.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rodney A. Marcom on Sunday, May 16, 2010 - 01:04 am:

Thank you all for your responses. I have good magneto output with the voltmeter/bulb approach cited above. The oil was a fresh fill before starting. Mag post is properly imbedded in the 'button'. Number 4 spark plug on mag setting when car is running and shorted out with a screwdriver from radiator support to the plug wire has little effect on the rpms. I have already started assembly and will install John Regan's plastic coil box 'wood', new wiring, new plug and mag wires and new timer (all due to Forum posts concerning the carbon trace from all the wet weather this car has been in the past 10 + years once I started really driving her again. I feel confident that she will then run stronger, smoother and have more power (high gear is lackluster at best at the moment).


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Patrick - (2) '26's - Bartow, FL on Sunday, May 16, 2010 - 02:37 am:

Your switch may be the problem. Sometimes the copper contacts inside the intrument panel switch are worn out, flattened out, or broken; or the pressed fiberboard circular pieces that the contacts are attached to are warped, or swollen out of shape. You will need to dismantle the switch to check if the switch is the problem. Be very careful. The bend down tabs that hold the switch parts together, break very easily and will only be able to take being bent open and closed only once. The usual Model T parts suppliers have repro switches or switch rebuild kits for this. Good luck. Jim Patrick


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Patrick - (2) '26's - Bartow, FL on Sunday, May 16, 2010 - 02:42 am:

PS. I just noticed you have a 1915. I was addressing the problem as if you had a 1926 switch. I'm not sure what type of switch a 1915 has or how it switches over from BATT to MAG, but my solution may still be pertinent if your 1915 has a switch with internal contacts. Jim


Add a Message


This is a private posting area. Only registered users and moderators may post messages here.
Username:  
Password:

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration