Perhaps someone can shed some light on this one.
My T starts on battery and runs just fine. While running on battery,
I have a circuit test light attached to the magneto post. The light shines bright and is consistent. This suggests that the magneto is operating properly. HOWEVER...when I switch to "mag" the engine continues to run for about 30 to 90 seconds and then quits.
I took apart the ignition switch. Everything seemed to be in order. I went ahead and replaced the ignition switch with a new one just to be sure. Same problem.
Any suggestions as how I might solve this mystery would be greatly appreciated.
Can we assume that if you leave it on battery, it continues to run well past 30 to 90 seconds?
Most are! MaHaHa! With the test light attached running on battery(the test light is your load, acts like the coils for the test), used a analog meter and check the actual output between the post and ground at different speeds. Don't forget to set the meter to AC 50 volt range. Idle, fast idle etc. Report back with the findings. Don't think it is the switch and may just have lower output then you think.
Magnetos are funny things, putting out "a sort of AC"current with a lot of weirdly intersecting sine waves. Forget the bulb, forget the analog voltage meter. Buy, beg, borrow, or steal a St. Louis mag tester, either original or from FunProjects. You will know in three seconds whether your mag is up to expectations. Since it probably isn't up to standards given the problem running you will the need to first check end play to ensure your magnets are not straying too near or too from the coil. If end play is not your problem then read Ron Patterson on how to recharge the magnets. Follow his directions and all will be well. Numerous threads on The Forum on how to check end play and mag output. Recently been there, done that, bought the tee shirt.
The St Louis mag tester, as far as I know works the same as the bulb and analog meter. It has a load and meter. The St Louis might used something like the windings from a coil for load. (?)
Someplace I have the plans on making one using the windings, and just were it is I don't know. It was posted sometime back and might have been on the old Ford International forum.
Missouri Mark has asked the right question! Does it run longer on battery?
"runs for 30 to 90 seconds and then stops." Mine does that every time I shut off the fuel and run the carb dry.
OP said it runs fine on battery. I agree that you need to measure the mag output with some sort of meter. Also, think about your coils. Before I rebuilt my coils, my car would run fine on battery, but just OK on mag. Lots of missing under load, etc. Not sure if that could get bad enough to not run at all on mag, but it's a thought. Might be worth finding someone with a coil tester.
What is your crankshaft end play like? Will it run longer on mag if you bring the engine above idle speed? Are your coils seated firmly in the coil box? Is your mag post clean and making good contact?
Response to the above:
1) Engine runs fine on battery. Have driven around the block.
2) Unsure what the crankshaft play is. Does this mean I have to
remove the engine? Ouch !
3) Coils. Coils are newly rebuilt and have been tested. They are
4) A fellow member of the local club has a mag tester and
is going to come over to perform an evaluation. First step.
Thanks again for your help.
Lots of potential "miss information" in your original post or at least some questions on my part. It is not clear what bulb you used in your test and also not clear that you perhaps didn't run the bulb ALONG WITH the coil at the same time which would be a double load and might very well make even a GOOD MAGNETO not operate correctly. When checking the magneto with a bulb and AC volt meter you need to make sure that the voltage can quickly go well above 20 Volts AC when you crack the throttle and go to higher RPM.
Mark G. - the St. Louis Tester does NOT work at all like the bulb and voltmeter quick test. The St. Louis tester is a test essentially of the quality of the magneto at ANY RPM and thus tells you instantly whether your magneto is totally OK for running your coils or NOT. The original post didn't mention who or what was used to setup the coils in the first place but poorly adjusted coils typically can run what appears to be OK on Battery and not very good on Magneto even on a good magneto. If you are going to use the results of a test to help you decide what is wrong then it is exceedingly important to run the test carefully and make sure you have accurate results or you can be off into the weeds chasing non existent problems. Hope this helps.
No you do not need to remove your engine to check for crankshaft end play,but you do need a dial indicator. A pry bar behind the front pulley gently move the crankshaft forward set your dial indicator to zero then move the crankshaft rearward, end play should be about .015 if it is more than that the flywheel may move far enough away that weak magnets would not induce a charge in your coil ring to fire the plugs. This is rarely the case but I have seen it.
This happened to me- honest-
My mag would quit at varying times. I'd pull the mag pick up looking for lint but nothing, and the motor would start up immediately and run fine...til the next time.
Finally, once I pulled the mag post and found a nickel sized, circular piece of aluminum stuck at the post, thus grounding the mag system.
Hmmm! It looked like the aluminum seal from a quart bottle of oil. I removed the seal and the mag as functioned for years now without quitting.
Unless there is a version of the St Louis tester for cars after 1919, it is using the coils as a load, is it not.
Craig, perchance are you any relation to the dearly departed Lindley and Ann Bothwell?
To Mark Strange:
Yes. Lindley and Ann Bothwell were my uncle / aunt respectively.
The "ranch" in Woodland Hills was started by my grandparents in
1927. My dad, his sister and Lindley spent much of their time
there in their formative years. Later, I also, spent much of my younger years there and, later, lived in my grandparents house (next to the shop) while in graduate school. Many fond memories.
Crankshaft end play can be measured approximately using feeler gauges. I tried measuring with a side-operating machinist gauge but it only had +/- .015 range. I used a feeler gauge between the fan belt pulley and block. The differences in my engine was .045". That was close enough for me to know that I need to address the problem. My car does not currently have a magneto but I will address that after fixing end play.
Hi Craig, Now you have some ideas and we can check both. I like to use Tom Carnegies method for charging the mag. I just bet that might fix it if your mag is weak!
Mark G: If you are running on battery, the coils are not in play. If on magneto, I think they would be. Would this make a difference in how the tester works?
Look at the instructions on the St Louis tester. Pre 1919 would have been running more then likely on magneto so would have been used in conjunction with coils operated by magneto. I think the instruction sticker is what would have been on the original one. In 1915 or there abouts, the magneto output was increased to operate the magneto powered head light, that is why the different reading between 1914 back and 1915. I think that the tester could be used on the 1919 up car while running on magneto but may not give a true reading while running on battery because there would be no load.
Here is a home made tester for checking while the car is running on battery. It is by Tom Carnegie. I would like to give credit to where I found it but do not recall.
Here's the latest with what we discovered with Craigs engine... It runs perfect on 6V Bat. When we switched to Mag it dies....
We tested the mag and it checks out OK. not Great but Good.
We checked the wire from the mag to the switch. Good.
We took the mag post apart and it looked Good.
He has a new switch and wiring which all looked great.
We also checked the Mag with a 1156 bulb and it looked perfect.
The Interesting thing, when the engine was running with the light bulb connected to the mag post and grounded to the oil line the car Ran FINE ON MAG! When I disconnected the light from the Mag post the car QUIT.
It will only run on Mag with something connected to the mag post going to ground, Sort of like a ground issue or needing a load to continue to run on mag.
We decided to quit for the day and think some more.
Gene Carrothers (fellow member of the O.C.club) was generous with both his time and his Mag Tester. I believe this particular tester is made by the folks who make the E-Timer. Anyway, we tested the mag and the tester registered a "good." Then we tried the time tested, 'old school' lightbulb
test. The intensity of the light varied with the engine's RPM's. AND the engine continued to run on mag while the bulb rested on the mag post. As soon as the bulb was removed, the mag stopped running. Crankshaft end play is within tolerance, so that is not an issue. THE COILS. The coils were recently rebuilt. When I picked them up, we tested them. They are O.K. Replacing the old coils with the new ones made a world of difference. Engine ran like it should...on battery.
Still an open issue. Will 'noodle' on it some more.
BREAKING NEWS....Dateline Costa Mesa, CA....Problem Solved. Repeat, problem solved. Bypassed the switch with a couple of wires w/ alligator clips. Truck runs just fine on mag. Looks like the switch (from China or wherever) is the culprit.
Anyone who would be willing to part with an original switch ('25 / 26)
in NOS or (very) good condition please get in touch.
You're very lucky that the bad switch didn't feed battery voltage through your magneto coils and discharge your flywheel magnets.
Here is a previous thread on the best source for switches: