Magneto Problem

[Derrick16]

Hey all,

My magneto has been running rough for about 3 months now. I’ve done my best to look for simple problems that might be right under my eyes. As of now, I’ve checked the mag post for any lint that might be stuck inside the hogs head and on the mag post itself. I’ve checked for any loose wiring from the block to coils to spark plugs. I’ve tried 4 different sets of coils from different people. I have also switched my rolling timer to a new day. 2 weeks ago, I decided to bring it into the Long Beach model t garage. The guys recharged it and the car ran perfectly. I drove 25 miles home on magneto. I last drove it a week ago with no issues, until this morning. I started the car up and switched over magneto to where it began to run rough again. I played around with the fuel mixture, and switched another set of coils, and still it ran bad. I looked for any loose wiring such as mag post, spark plugs, etc and still the car ran rough. I’m not sure what to do at this point. My question is what could occur during the time when it was running perfectly on recharged magnets and now. If anyone has experienced the same thing, I’d love your thoughts on what the issue could be. I’m assuming it could be a bad field coil, something floating around in the oil, or something internal that I just can’t see. I’m just stumped at why it run good after a recharge and then go back to the way it was. I’m considering perhaps going with an alternator to bypass the magneto all together as pulling the engine out isn’t in the cards for me at the moment. I appreciate any info and thoughts. Thanks!


Derrick

[Moxie26]

Does your car have a original style ignition switch, or is it a modern repro switch?

[Derrick16]

I have an original switch. My wiring harness are about 2-3 years old. I should also note that the car does run good on battery.

[JTT3]

Derrick though you will hate doing you may need to remove the starter. Take the Bendix off first! Once removed from the bendix cover side & with someone turning the motor with the hand crank(take the plugs out to make it easier) inspect the face plates on the magnets to see if one ore more have come off. Sometimes you can actually see them with a light and then sometimes you have to take your finger and feel for them. Sounds like from the mag issue you may have lost one or more face plates. If so your problems could’ve compounded and damaged your field coil, That’s when the fun begins requiring you to remove the engine. The other is you have so much wear on the 3rd main the gap between the field coil and flywheel is so great that it can’t produce the voltage needed to power the coils. Hopefully not. I don’t know much but that is one possible reason for the mag suddenly to stop working.

[nicklm]

A little while ago we had our motor taken apart since we needed valve work and other issues fixed. We added a higher compression head and all went well and it ran very good on magneto, for a while. The car did run well on battery and started to falter on mag. As you did, we looked everywhere, I thought.
Look at the wire diagram and you will note that there is a connection on the firewall with a screw onto a wooden block. It is the second screw from the left end.

We found that this screw was not tight and that caused the magneto to run less that great. Look at these screws and make good connections.

Lately we had another issue with the motor occasionally skipping at no particular speed. Looked for the problem in the daylight and could not find an issue. One evening when it was getting dark outside, with the hood up, I noticed a spark from the low amp wire on the coil box (1926 under hood) was sparking to the high tension wire going to the spark plugs. (Maybe from the sparkplug wire to the low tension wire?) Bend the sparkplug wire away from the other wire. That stopped the occasional miss.

Hope either of these areas may cure your problem. Answer is out there and you just need to find it. AND POST THE ANSWER for others to gain the knowledge. Good Luck.
Nick

[MichaelPawelek]

Someone correct me if I am incorrect but cannot the rear main crankshaft bearing wear on the face enough for the crankshaft to move back and forth where the gap between the flywheel magnets and coil faces change and become too wide for the magneto to work properly?

Lang’s has this accessory shim to place at the front of the crankshaft to temporarily correct this situation.
https://www.modeltford.com/item/3030SHIM.aspx

[Steve Jelf]

Someone correct me if I am incorrect but cannot the rear main crankshaft bearing wear on the face enough for the crankshaft to move back and forth where the gap between the flywheel magnets and coil faces change and become too wide for the magneto to work properly?

Yes, that's true.

Nick's comment about the terminal block reminds me of having the same trouble. In my case the screw was loose because the terminal block was cracked. A new block solved that problem.

[Derrick16]

A little while ago we had our motor taken apart since we needed valve work and other issues fixed. We added a higher compression head and all went well and it ran very good on magneto, for a while. The car did run well on battery and started to falter on mag. As you did, we looked everywhere, I thought.
Look at the wire diagram and you will note that there is a connection on the firewall with a screw onto a wooden block. It is the second screw from the left end.

We found that this screw was not tight and that caused the magneto to run less that great. Look at these screws and make good connections.

Lately we had another issue with the motor occasionally skipping at no particular speed. Looked for the problem in the daylight and could not find an issue. One evening when it was getting dark outside, with the hood up, I noticed a spark from the low amp wire on the coil box (1926 under hood) was sparking to the high tension wire going to the spark plugs. (Maybe from the sparkplug wire to the low tension wire?) Bend the sparkplug wire away from the other wire. That stopped the occasional miss.

Hope either of these areas may cure your problem. Answer is out there and you just need to find it. AND POST THE ANSWER for others to gain the knowledge. Good Luck.
Nick

I will certainly check now! Thanks for this info.

[Derrick16]

Derrick though you will hate doing you may need to remove the starter. Take the Bendix off first! Once removed from the bendix cover side & with someone turning the motor with the hand crank(take the plugs out to make it easier) and inspect the face plates on the magnets to see if one ore more have come off. Sometimes you can actually see them with a light and then sometimes you have to take your finger and feel for them. Sounds like from the mag issue you may have lost one or more face plates. If so your problems could’ve compounded and damaged your field coil. If so, That’s when the fun begins requiring you to remove the engine. Hopefully not. I don’t know much but that is one possible reason for the mag suddenly to stop working.

I will definitely look into that when I’ve exhausted all the easy options first. Thanks for this info!

[jab35]

I'd suggest looking inside the transmission magneto plug hole and transmission cover with a video inspection scope or a borescope before removing the starter. If you don't have a scope they can be had for under $50 which for me is a far better return than removing/replacing a model t starter. YMMV, good luck, jb

[nicklm]

Did you find an answer to the problem?

[Ron Patterson]

A Model T Ford that will not run correctly on the Magneto and will run correctly on the Battery is the classic symptom of improperly adjusted ignition coils. Try the easy things first, then check the Magneto output.
Ron Patterson

[Ron Patterson]

Oops, I see you tried another set of coils.

[TXGOAT2]

I would disconnect the magneto and connect an AC voltmeter between the magneto post and engine ground. Place the voltmeter where you can observe it while driving the car on battery. Make sure your connections are secure. The magneto should provide from around 6 or 7 volts at very low engine speeds up to 25 to 30 volts at higher engine speeds. The meter should show voltage changes with engine speed changes, but voltage should not change at any steady engine speed, and it should never go to zero with the engine running. Use the 0 to 50 volt scale on the meter. A cheap parts store multimeter is fine for this job.

[modeltbarn]

By chance is your problem after washing your car? I had something similar, and I didn't tie it together with car washing for some time. My symptom was running rough intermittently. One afternoon after washing the car I got shocked when I touched the coil box; turned out I had a carbon trace in the wood, and the Fun Projects rebuild kit took care of the problem.

Just one more thing to look at....

[Steve Jelf]

Derrick, I didn't see that you identified the car. This is the 1916, isn't it? That would negate any advice involving the starter.

[Norman Kling]

Before doing anything else, try this. Remove the wire from the magneto post to the terminal block. Tape up the end. Then take a wire from the battery terminal and connect to the magneto terminal on the block. Now start up the car on battery, and then switch the key to magneto. The car should run on battery in either position of the key. Now drive around a while and see what happens. If it misfires in the magneto position of the switch, you have a bad connection either on the wire or within the switch. If it runs fine in both positions your switch and wire between the switch and the block is good. Then you can remove the jumper wire and re-connect the magneto wire to the terminal block. The problem is elsewhere. Ron Patterson is right. The coils can be adjusted to run on battery but misfire on magneto. You could also have a timer problem. On battery, the coils will begin to spark as soon as the magneto contact is made and continue to spark until the rotor leaves the contact, however with magneto, the coils will spark when the AC reaches the proper level which would be somewhere in the middle of the contact. So if the rotor doesn't make good connection at that point, you will get little or varying spark.
Another thing which is normal is what I call "Nodes" When you are running on magneto, and advance the spark the speed of the engine will suddenly speed up as the lever is moved. That is a normal thing, however, if the coils are not adjusted evenly, you could get one sparking before another because of the coil adjustment.
Check all these things before you dig into the engine.
Norm

[Steve Jelf]

As usual, Norm's suggestions are on the mark. But if this is the 1916 there is no terminal block. In that case, disconnect the magneto wire from the coil box and tape the end. Then install a jumper wire from the battery terminal on the coil box to the magneto terminal on the coil box, leaving the wire from the battery connected to the BAT terminal.. Then you can test the switch as Norm described.

[Norman Kling]

I will clarify something which I said which could be misinterpreted with disasterous results.
When "I said to connect the battery terminal to the block", I meant the terminal block, NOT the magneto terminal on the top of the hogs head.
Norm

[Derrick16]

As usual, Norm's suggestions are on the mark. But if this is the 1916 there is no terminal block. In that case, disconnect the magneto wire from the coil box and tape the end. Then install a jumper wire from the battery terminal on the coil box to the magneto terminal on the coil box, leaving the wire from the battery connected to the BAT terminal.. Then you can test the switch as Norm described.

Steve, this is the 1923 touring.

[Derrick16]

By chance is your problem after washing your car? I had something similar, and I didn't tie it together with car washing for some time. My symptom was running rough intermittently. One afternoon after washing the car I got shocked when I touched the coil box; turned out I had a carbon trace in the wood, and the Fun Projects rebuild kit took care of the problem.

Just one more thing to look at....

Interesting, I just got off the phone with a friend and told him the only place I have no looked at is the coil box. I don’t recall washing my car as it’s been in rough shape recently, but I will give it a look just to cover all the bases. Thanks for this info!

[Derrick16]

Before doing anything else, try this. Remove the wire from the magneto post to the terminal block. Tape up the end. Then take a wire from the battery terminal and connect to the magneto terminal on the block. Now start up the car on battery, and then switch the key to magneto. The car should run on battery in either position of the key. Now drive around a while and see what happens. If it misfires in the magneto position of the switch, you have a bad connection either on the wire or within the switch. If it runs fine in both positions your switch and wire between the switch and the block is good. Then you can remove the jumper wire and re-connect the magneto wire to the terminal block. The problem is elsewhere. Ron Patterson is right. The coils can be adjusted to run on battery but misfire on magneto. You could also have a timer problem. On battery, the coils will begin to spark as soon as the magneto contact is made and continue to spark until the rotor leaves the contact, however with magneto, the coils will spark when the AC reaches the proper level which would be somewhere in the middle of the contact. So if the rotor doesn't make good connection at that point, you will get little or varying spark.
Another thing which is normal is what I call "Nodes" When you are running on magneto, and advance the spark the speed of the engine will suddenly speed up as the lever is moved. That is a normal thing, however, if the coils are not adjusted evenly, you could get one sparking before another because of the coil adjustment.
Check all these things before you dig into the engine.
Norm

Thank you Norman, this is a lot to dive into. I will certainly try the tape option and see what happens. It also wouldn’t hurt to perhaps try another set of coils. Something will eventually click. I just hope I can find it before resorting to pulling the engine. Thanks for the Info Norman!

[Derrick16]

Did you find an answer to the problem?

Not yet unfortunately. Today I switched ignition switches off another car that I know works as well as replaced a new terminal block. Still nothing. =\

[Derrick16]

I will clarify something which I said which could be misinterpreted with disasterous results.
When "I said to connect the battery terminal to the block", I meant the terminal block, NOT the magneto terminal on the top of the hogs head.
Norm

Noted, thanks!

[TRDxB2]

Did you find an answer to the problem?

Not yet unfortunately. Today I switched ignition switches off another car that I know works as well as replaced a new terminal block. Still nothing. =\

Since the car runs fine on BAT but not MAG, logically the problem is with the the MAGNETO portion of the circuit (see wiring diagram for magneto to switch). MAG & BAT use the same coils, plug wires etc. so everything from the switch to the motor potion of the circuit is the same for both. So one can assume the problem wouldn't be expected to be in that end of the circuit. Yes there is a contact difference in the switch that chooses the voltage source MAG or BAT so it is from there back to the source that the problem is expected to exist.
Again if it ran rough before the Long Beach T guys recharged it and then it ran perfectly afterwards they recharged your magneto and now after some time it runs rough again that would suggest the problem is with the magneto. So I would focus your efforts on the suggested Magneto checks above.
Here is a simple test for magneto voltage output.

MAGNETO_TEST-760271.pdf

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