Yesterday I asked a few questions about why my truck quit running on the magneto. I tested the wires and everthing seemed fine. Then I put the tester on the magneto post and it acts as a ground. Is this normal?
It is like 1/4 ohm to ground through that post if everything is fine with the field coil.
You need to run on battery and load test the magneto with an 1156 bulb. At low idle, it should glow. At high engine speed, it should blow. Simplified mag load test....
If you use an ohm meter on the magneto post when the engine is not running, it will read as a ground. That is a good sign. If the engine is running on battery, and you put an AC volt meter on it, you should read a voltage. Use a 12 volt light bulb to ground as a load on it and measure the voltage across the light bulb. You should get 5 or 6 volts at idle and up to 30 volts at higher speed. The voltage increases as you increase the speed of the engine. An analog ac volt meter works best. The digital meter will jump all around and you won't get a very accurate reading. If it is good the light bulb might burn out. If you get that voltage, the problem is somewhere between the magneto post and the coils.
If the voltage is low or non existant, the magnets need to be re-charged or there is too much clearance between the magnets and the magneto coil ring.
"voltage across the light bulb" could someone draw me a diagram! I am still not sure what or how that is done.
MarkG and Nellybell
The 1156 bulb is connected in parallel with the two test probes of the analog ac voltmeter.
Here is the complete test set up and expected results.
Go to your local auto parts store and buy a #1156 bulb. This is commonly used as a back up light bulb in modern cars. This bulb will come close to simulating the load of a typical Model T coil. You may also want to pick up a socket for it too and put some wires on it to make a regular test light out of it.
Connect the bulb across the magneto output and ground while you running the engine on the battery with the emergency brake pulled all the way back and set. Using an analog voltmeter check the AC voltage across this bulb as a load.
Provide the following test results back to us via email:
AC Voltage reading at engine idle:
Lamp Brightness at engine idle:
AC Voltage reading at engine moderate speed:
Lamp Brightness at engine moderate speed:
AC Voltage reading at engine high speed:
Lamp Brightness at engine high speed:
A good magneto will produce at least 7–8 volts AC across this load at a brisk idle.
If your magneto output passes this test it has sufficient output to power properly adjusted coils.
Ron the Coilman
Disconnect the wire from the mag post. With the engine running at a fast idle or more, short the post to ground with a screwdriver. You should get a lot of sparks. The faster the engine speed the better sparks you should have.
This is from the March/April 2007 Vintage Ford magazine
Analog type mandatory!
Ron the Coilman
I wish to confirm what Ron has stated with regards to analog meter. The meter pictured is obviously a digital type and these simply cannot be used to measure the magneto output if the engine is running since the ignition spark noise will radiate into the digital meter and give you totally erroneous readings - or not. I have had folks disagree on this but it really has nothing to do with the quality of the digital meter used. I have Fluke lab grade meters and Harbor Freight cheap ones and they both are interfered with by the ignition noise so close by. You might indeed have a digital meter that will work on some cars but It is not a case of the reading but slightly off or partly off - it is just totally unreliable to try and do it this way since you simply cannot rely on the reading regardless of whether it is good or bad. If you can - Pick up a super cheap analog meter that can read AC volts up to about 50 on a reasonable scale and use that. It seems the T being a cheap car wants to be tested by a cheap tester ha ha. The diagram is totally correct as to connection. The average new 1156 bulb will burn out in exactly 6 minutes of sustained operation at 28V. Of course there is no way to know if you have an average one ha ha.
Thank you Ron and John. I kinda thought thats what was ment, but for some reason it just did not click.
I tested the volts on mag post ,with motor running.There was very little volts if any.Looks like full tear down.If I may ask ,what parts do you normaly replace in a case like this?Thanks.
Dave -- Take the mag post out and check it before tearing things apart. That may be the culprit.
Before taking the engine apart, you can try to recharge the magnets in place. There are threads in the forum that explain how to do this. You need a north pointing compass for this and 2 12 volt batteries. If done correctly, this can revive your magneto unless you have too much endplay in the crankshaft.
My 26 won't run on magneto at slow idle, but moderate idle runs OK. I get some stumbling when I switch from 12 V to magneto at moderate speed, and the switch is sensitive to position. The engine runs better with the timer advanced 4 or 5 notches MORE with mag than with 12V. I tested it using a 1156 bulb and a new analog meter like above. Slow idle gave me 6.5 volts and a dim bulb, moderate speed bright bulb and 18V, throttle pulled all the way down gave me 28V and a very bright bulb, but no burn out of the bulb. Even trying to richen the vaporizer carb still gave me a red glowing exhaust manifold at 1/2-full throttle and full advance. This car tops at about 30mph and has what looks like a recent rebuild (full stack of shims, shiny bores with hash marks, aluminum pistons). I'm just starting an engine pull to check the mag gap and tranny alignment. There doesn't appear to be any significant movement on prying the crankshaft for and aft. If I can check tranny alignment and replace the bands by just pulling the hogshead, I'd rather do that. I just feel my mag is weak.
Boy that is somewhat perplexing. I have to agree that 6.5 V at idle is kinda weak unless your car is capable of a very slow idle unlike most of my T's. The full throttle 28V seems strong enough but what I wondered most about was the statement that your exhaust manifold got red - that has always led me to running with retarded timing. Have you checked the timing using the PIN on the front of the engine at 3:15 O'Clock with full retard on lever? Is your timer control rod routed such that there is no lost motion in the timer advance? We never talk about the amount of timer rotation that you should get when you move the lever but if your lever-to-timer-rod linkage is sloppy and perhaps hitting something along the way - that might limit your advance and cause the red manifold. Usually coils that run on 12V but NOT on magneto when the mag voltage is healthy are coils that need to be adjusted. Are you coils set up via HCCT? I am really curious about this one and would like to stay in the loop until you find this.
I have one of Frank's new timers and set it to buzz just past TDC with the "wire on the piston" method. The pin is just below 3:00. There is some slop in the rod. These are the coils that Ron set and said were the "ugliest coils he had ever seen". I'll try to check timer rotation this weekend if the pager is quiet. This engine will idle slower than my 23 on 12 volt, but dies on switching to mag at that slow a speed. It will run at a faster idle on magneto.
Where is your spark lever set when you idle the car? With the spark set a few notches down it will idle better on mag. I would think, you have some problems with the vaporizer running too lean even when you adjust the needle.
Norm, Once I start it, I pull it down 4-5 notches to idle. It likes a bit more on magneto. I agree the vaporizer is likely too lean. there may also be a leak between the manifold and block. I plan on replacing the vaporizer with a NH or LF Stromberg that are sitting around. I've just got to straighten a spare exhaust manifold and drill a hole through the block between 2 and 3 for the carburetor rod. I don't mean to steal this thread, but the difference between battery and magneto has me perplexed.
The only vaporizer I have is in a box in the garage. I think that maybe the idling circuit is working ok, but it doesn't get enough fuel at higher speeds. Your car should go about 45 MPH at top speed, and faster downhill (don't drive it that fast for prolongd periods) You could also be getting warped valves because the exhaust valves could be getting hot as well as the manifold.
If the car will not to faster than 30 when you are running on 12V - you have problems that even a perfect magneto is not going to fix. Before you pull the engine to fix the magneto, best to do more diagnostics since the magneto is NOT the main problem and may not be any part of your problem. Just my .02 but my T will run well in excess of 45 with 12V battery powering my coils.
Thanks for all of the tips on tracing magneto problems.Im sure they will be usefull in the future.Thanks also goes out to Mike,I pulled the mag post off my 25 coupe , put it in the TT .What do you know,it runs on the mag again.
Does the bulb have to be yellow?
Will a red or blue or clear one work good enough?
Dave-I may have missed this in the above excellent posts.Could your lack of top speed and red manifold be caused by a badly worn timer race?I have had this experience.I have also had a similar problem with a New Day timer.Put on Andersons.No more timer grief.
Jim, I'm the guy with the lack of top speed and red manifold. I have a new Anderson on the car.
Ooops.I was trying to 'multi-task' when I read through this thread.Doctor,if you would happen to need a valve cover with a throttle rod hole,I have plenty. I'll send you one,as Ford Motor Co. used to say,'gratis'.Some swear by vaporizers.I don't.I swear at them.
Noel,a couple other problems that could cause the symptoms your '26 has.Cam gear not installed on marks. Off a tooth.Pulled this boner myself as well as have figured out others mistakes. Mouse, mud dauber,etc.nest in muffler.Mine ran really strange and strangled. The mouse nest was fireproof insulation so it did not smoke and stink.These pests that build nests in things are a real pain.Once I built an engine that only ran on cylinders three and four.After much checking and frustration,I discvered mud dauber wasp nest in front of intake manifold.
Thank you, gentlemen. I am going to try to get to the engine this weekend, pending hospital calls.
I found what I think is at least part of the reason for the lack of speed over 1/2 throttle.
Now that very obviously should be part of the problem but according to Murphy's law, the more obvious the difficulty found, the less likely it has to do with anything that concerns the problem ha ha. That would seem to limit your breathing and it at least is not the magneto either. I want to get a bet down that the magneto is not the issue that eventually makes this baby go. I guess I am wondering why the pipe was routed as such. Is the muffler the "standard" T setup or is there something back yet even further that needs a looksee? I am thinking you are hot on the trail now.
Looks like the pipe was dented to clear the home made Ruckstell shifter?
This T has been a poor runner since I purchased it last year. It was converted to 12 volts and the cutout recently started sticking, so I disconnected it and grounded the generator until I convert back. I have one of John's VR's. This weekend I found the throttle rod seems VERY loose in the vaporizor carb, likely causing a leak. I don't plan to overhaul the vaporizer, but replace it with an LF or good NH. The ignition switch is "touchy" on switching to mag, sometimes not making contact. I wonder if that is some of the reason for the poor performance at very slow idle. There is no palpable movement of the crankshaft for and aft so, if it was set up right, I doubt if the magneto gap has increased. The muffler is a stock T muffler that was tack welded to not come apart. The rest of the pipe is open except for a small dent a few inches from the manifold. I agree with Royce, but it appears to clear without the dent being made. The engine appears to have had a very recent rebuild with all visible internal bolts wired and the wire tightly twisted between bolts (crankshaft to output, drive plate). The camshaft also feels tight. I think I'll replace the tail pipe and carb, button it up, and try it again. I don't know whether to try to overhaul the ignition switch or send it off.
With the combination of loose throttle rod (which would make the car run lean) and the choked exhaust pipe which would increase the back pressure, I would think your manifold would get hot, and your car would be slow. Fix those, and you will probably have a much better running car.