The engine in my '27 Touring was rebuilt 3 years ago at which time the field coil was redone, the magnets were charged individually and the end play was set at .004. The mag has consistently put out over 20 volts at high idle. I have less than 1,000 miles on the rebuild. The other day while cruising at 30 mph the mag quit without warning. I checked the magneto post contact, swapped out another known magneto post, and replaced the switch from another running car and still nothing. Volt meter shows no output from the mag post. I have pulled the hogs head and everything looks fine. The magnets seem weak but I would think they are still strong enough to put out some voltage. The only explanation I can think of for losing the mag would be if either the mag or battery terminals on the switch got loose and touched the other. Now that I have the hogs head off is there a way to check the field coil for shorts before I try to recharge the magnets and put the hogs head back on or is there something else that I am missing here? I am electrically challenged to say the least so I need all the help I can get!
I'm in the same boat and will follow this thread now
If the magneto ring isn't somehow messed up and shows good continuity (no broken circuit, check with ohm meter), a couple critical parameters might be magnet strength and also the gap between the magneto coil ring and the magnets. Just off the top of my head, I seem to recall that gap should be between .025"-.040" (check the repair manuals).
An interesting conversation from the past: http://www.mtfca.com/discus/messages/118802/126308.html?1267144376
Val, did you replace to wood in your coil box? It's unlikely but, I had a problem where my mag kept dying because the wood in the coil box was carbon tracked and the current from the spark plug terminals kept getting into the strip in the bottom of the box that's connected to the magneto when the engine is running on mag. I recharged the magneto in the car then I removed the ground strap from the battery and grounded the generator so that I knew the battery could not possibly be shorted out to the magneto and it still died. That happened three times before I figured out what the problem was. If I were you I would take the ignition switch out and check for continuity between the magneto and battery terminals on the back of the switch in all switch positions. The two should never be connected. If they are the switch is bad. If not the problem probably lies in the wiring somewhere. If your coil box still has the old wood in it I would replace it with the composite set that fun projects sells just to prevent having problems if the box gets wet. As long as your magnets aren't completely dead you should be able to recharge the magneto in the car.
Val, you stated there is no output at the mag post with the engine running on battery and the magneto strength checked with a volt meter. Is that correct? It seems if the wood in your coil box was a problem the car wouldn't run on battery.
Michael, even if the wood is carbon tracked the car will run. Like I said more than likely that's not what his problem is but, it's a possibility.
Val, any chance the Mag winding have come loose from the contact block? I have seen this. I can't come up with a scenario where battery voltage gets mixed up with the Mag while innocently driving along.
Above should be windings. I definitely recall this happening to a friends rebuilt Mag.Was a puzzle,as this was nothing apparent until wiggled the contact block. Hoping this is problem..Easy fix.
Stephen, my point was, if he measured the voltage at the mag post when the car was running (his words, not mine) and saw -0- voltage the problem is in the magneto. I'm assuming (I know, that's dangerous) he unhooked the mag post before measuring voltage. Also, if his magneto is producing electricity and the mag post is hooked up why would the electron flow from the magneto be different than that from the battery? Is DC voltage less affected by carbon tracks than AC electron flow?
It seems to me he's isolated the problem to the magneto. (?)
Was the output checked using the AC setting or DC. Need to use the AC setting to check. This has come up before. If you use the DC setting you will get 0.
Mark, good point! Did he use a digital or analog voltmeter? There really seems to be some information missing. I guess until Val provides some of that information were caught having to make assumptions. He did say he's electrically challenged. And I admit, I am too. For now I'd like to understand Stephan's logic because he's probably a lot more knowledgable than me and I'm here to learn.
I dealt with a mag once where a cotter pin had broken and was picked up by the magnets which jammed it into the winding at about the 7:00 position, grounding it there and reducing the voltage to about 2. A similar thing could have happened to one of the windings close to the first one, which would give a reading close to zero.
I checked with an analog meter on the AC scale directly from the mag post. I did get a very slight movement of the needle but considered it to be too slight to calculate the output. I have replaced the wood in my coil box with the composite kit and my switch was rebuilt by Ben Martin a couple of years ago. The mag terminal and the battery terminal on my switch appear to be close enough that if the mag wire got loose it could possibly make contact with the battery terminal and that is what I was thinking might have happened. The contact block on the mag ring is secure. My plan is to recharge the magnets and put things back together at this point because I can't think of anything else to do. I am wondering how weak the magnets need to be for the magneto to not work at all and if there is a way to determine if there is a break in the windings or a short of some kind. When I hook the ohmmeter to the pick up block and ground it I show continuity.
I'd say if the gap isn't excessive, recharge and drive on. Well, you might want to do a good inspection of the wiring, etc, but it's very probable you lost magnetism. At any rate I hope you get it sorted out.
Several things can happen. Magneto too far from coils due to endplay in crankshaft. Magnets need charging. Contact not making good connection in hogs head. Magneto coils open, shorted, or grounded. If you put an ohm meter between the contact and ground you should get a very low resistance. If open you would get infinity reading. A short or ground would be almost impossible to find with an ohm meter.
Michael, read my post again. I said in my case the coil box wood is what killed the mag in the first place. The car was running fine on the mag then it started missing then the mag died.
Val, hopefully you're right that the battery accidentally got connected to the magneto. If the magnets are really weak the engine won't run on mag but, they would have to be pretty dead. I rebuilt a magneto once where the magnets were so weak they would barely pick up 2 pounds and the car still ran on mag just very poorly. When the coil box wood on my coupe shorted out it killed the magneto completely. The mag put out absolutely nothing. Try and charge the magnets in the car with a couple batteries if everything else appears ok.
Thanks to all for the advice. I am trying to line up three 12 volt batteries for an in car magnet charge while the hogs head is off and will post the results when everything is back together.
Hi. Check the little triangle block hasn't split, and earthing out your mag. I had same thing with mine. I found I couldn't recharge the mag, as every time I put power to mag post I would get a small explosion from fuel in oil. It was hard to see as the dome of solder covers it. Changed block in car and all good. Voltage jumping to rivit that holds block. Sometimes its the simple things. Chris n.z
Is it possible to find a short or ground while the mag ring is in the car and if so what is the process? Obviously, I can't fully examine the bottom of the mag ring without pulling the engine but would hate to pull the engine if that is not the problem.
"When I hook the ohmmeter to the pick up block and ground it I show continuity."
You should read aproximately .5 to .75 ohms on that check.
"They" always say 36 volts for an in-car magnet recharge. Has anyone every tried 12 volts? I suspect it would work but have never tried it.
Ken, I did it once with only 24 volts and I could easily crank the car on mag.
I used 18 volts once by placing 12V car battery in series with the 6V battery that was already in the T. Did that with jumper cables but be careful that the cables don't pop off during the charge. It worked fine for awhile but the magneto had other issues so can't say we exhaustively tested our results.
Hope this helps.
Val, I was curious what was the test you initially performed on the mag post that caused you to decide to replace it? I have seen a lot of cars have more problems "installed" by swapping parts hoping that something magic happens even though the reason for the swap was just a guess. Not a good procedure. Better to diagnose first. Committees formed up to present a myriad of possibilities can have you chasing a lot of wild geese and stepping on some good ones without noticing it. Been there.
I think it would be hard to find a short unless you base lined the magneto coil resistance prior to installation. Short to ground would lower the resistance
Have you done any testing on the mag yet? If the mag has an open that would be easy find, mag post or mag terminal to engine block. If you get an infinity on your ohmmeter you have an open.
I would think even with a short you might still get some output to the mag post but it would be very low.
John, when the mag quit I removed the mag post to check for lint on the pick up and found none. I have a set up for a front oil delivery system on the car so I pulled that and put a mag post on from a running car that did not have an outside oiler with no improvement. I then replaced the switch with one from a running car with the same result. At that point I decided to pull the hogs head rather than try an in car mag charge first but the reason I did that was because the cams were worn on the one in the car and I had rebuilt another one to replace it but was putting it off because it is a big job and the car was running OK (I used washers to make up for the wear on the cams as a temporary measure a year ago). What I found when I removed the hogs head was that the magnets were very weak. Since the mag was very strong before the failure and everything looks good from what I can see I suspect that the mag connection on the switch loosened up and touched the battery connection weakening the magnets. They are definitely very weak so I will try to remagnetize them and see what happens. With a bad back the last thing I wanted to do was pull the hogs head but I had tried everything I could think of first with no success. If that does not work I will pull the engine and start from scratch because I have never had a T that did not run on mag and I am not about to start now!
Val, I, and probably many others on this forum can sympathize with your situation with your back issues. Over the years I've had several surgeries as a result of some crushed vertebrae and some disks that are just too darn far gone. Last year it flared up and working on my beloved Model T's has been tough. But I learned to slow down and handle only what my body will let me do. The days of working on them like I'm in a marathon are over. Doc says the calcium deposits, bone spurs and arthritis in my back is going to be permanent now. But, even with the back issues I'm still good for an hour or two each time I go out. It's surprising how much a guy can get done by taking it slow. I'll say a little prayer that you'll get this mess sorted out and you're back driving your Model T real soon.
In my second post I listed a past thread from this forum that speaks to measuring individual magnet strength in the car.
Assuming a continuity test on the coil ring shows good, wouldn't a test for magnet strength using either a gauss meter or one of Fords meters suffice to determine the strength of the magnets?
In that thread they spoke of a measurement 50 of what ever Fords units were as good. It seemed there was a threshold of 320 gauss being minimally effective and 700 gauss making the magnets capable of lifting three lbs.
If the continuity of the coil ring checked good, and if the measured magnet strength checks good, is the next critical parameter the air gap between the magneto ring and the magnets. Because to me, with my somewhat limited knowledge and twisted way of thinking it would seem that "borderline" good magnets With the air gap at its most "open" allowance might have a real bad effect on the way the car would run on mag.
When I read Val's first post it seemed Val is asking if there's a way to possibly measure these three parameters and the older thread seemed to answer his question.
The reason I bring this all up is because there's a fellow in the wings named Chris Laughery who's following all this and hoping for some direction on getting his magneto workin again.
Mike, thanks for the back support, no pun intended! Believe me, I pace myself these days but those later cast iron hogs heads with the heavy boss for a starter are a real pain.
I have no end play to speak of and the mag was set up with the proper clearance. The mag has always been strong since the rebuild. The magnets are very weak compared to the way they were when the engine was rebuilt a couple of years ago so I know they need to be recharged. The question is what caused the weak magnets all of a sudden with no prior issues. I am just hoping I can correct the problem without having to pull the engine and start messing with the coil ring!
Val, I hear what you're saying. But I also read Stephen's post above that even with "borderline" capable magnets he was still able to get the engine to run on mag but poorly. I was thinking a way of measuring those magnets strength while in the car would give you some confidence in whether you want to pull the engine or not. So, my next question is: how did you determine they're so much weaker? Then, can your method tell you enough about the strength of the magnets to make that decision?
Please bear with me and what must seem like my probably dumb questions. I'm trying to learn but also know that there's a point where I could be getting to be a pain in the butt.
Also I understand getting to the root cause for losing the magnetic strength is a priority to keep it from happening again. And I hope you've isolated the problem and are able to correct it.
Mike, I have no way to measure the strength of the magnets other than by how difficult it is to pull off a keeper plate and right now it doesn't take much. They will hold the keeper but it can easily be removed. I am electrically challenged but assume that with the wire from the mag pick up off and and using an analog meter from the pick up to ground since I only get the slightest movement on the meter either those magnets must be very weak or there is something wrong with the coil ring. If I do an in car charge and the magnets hold their charge I will assume it was something that demagnetized them and that the mag coil is OK. I will then put the hogs head back and see what I get. If that does not work I will have to pull the engine. I know from past experience that coils can be adjusted to work, albeit poorly, with a weak magneto but when they are set up to run with a good mag they will not run. My coils were set up by Ron Paterson to run on a good mag which might explain why the car wont run on mag although I think the mag is not putting out enough to fire the coils regardless of how they are set.
Thank you Val. It seems you actually have quite a bit going electrically. I kinda have a feel for how sensitive these systems can be and truthfully they make me nervous when I have to think they might go south someday while I'm out on the road.
Thank you for being patient with me and now I'll fade back into the distance and only come out when I find a need to get someone else to wonder; "if I ate too many paint chips" as a kid.
I had a similar problem with two magnetos. I went through all the tests and isolated the problem to the field coils. In each case the screw that holds the contact button washer to the triangular block was too long and grounding out on the rivet that holds the block to the coil frame. RV Anderson sells a new block, washer, insulation, screw and rivet for $15. The block comes pre tapped for the screw. The new blocks are very tough allowing a shorter screw to hold the washer without fear of contacting the rivet.
To check for this problem, remove the soldered contact button, the washer and screw and place one lead of a continuity tester in the screw hole with the other lead on the coil frame. If there is continuity, current is passing from the screw to the rivet and grounding the coil.
Thanks for that tip Richard. Did the problem develop after time or was it an issue from the time the coil ring was initially installed? I will give it a try. Mike, I have owned Model T's for more than 40 years and have 7 of them now. This is the first time I have run into a mag problem that has me stumped and believe me when I say I know nothing about electricity. The system is actually quite reliable so I wouldn't be to concerned. The real problem with the mag is that if you have a problem it can require pulling the engine to correct because of where it is located. That is why so many T's are running on battery. Only one of my cars has a starter but I keep a battery on board to make cranking a bit easier on my back and if you keep a battery on board you can always switch over to battery and make it home if you have a problem with the mag.
"I am electrically challenged but assume that with the wire from the mag pick up off and and using an analog meter from the pick up to ground since I only get the slightest movement on the meter either those magnets must be very weak or there is something wrong with the coil ring."
Val, the strength of the magnets has nothing to do with the the resistance of the coil ring. The strength of the magnets only come into play when the engine is turning.
Measure the resistance of the coil ring w/a digital meter, you should read approximately .5 of an ohm.
Interesting enough both failures occurred only after the coil was in service for a while. Only thing I can figure is there was a bit distance between the screw and the rivet and it took a while for the current to create a path. When I examined the block I saw that the screw hole was open all the way to the rivet. Don't know if it was drilled that way or not. If so, the maker relied on the air gap between the bottom of the screw and the rivet to keep from it from grounding out. Whatever the case, they went dead all at once and there was no current coming to the mag post.
Ken, I borrowed a digital meter and it shows .5 ohms so I guess that checks out. Tomorrow I will do the test Richard suggested and see what I get. If that checks out too I am going to charge the magnets, put the hogs head back and hope for the best. I am still thinking that the battery and or mag connection on the back of the switch got loose and touched causing the magnets to die. When you look at how close they are it is certainly possible.
Val, Also check that the switch plate isn't conducting electricity. That can happen with age and contamination. I have seen that with my original switch plate and had Ben Martin replace it with a modern unit that works well. Actually connect a battery to the battery contact and see if you can read voltage across the plate or to contacts that shouldn't have power.
I don't like the idea of unsoldering the magneto connection to see if the solder pile is shorted. The more things like that you do the more likely it is that you will put in a problem. Since your plan is to recharge the magnets anyway - why don't you simply apply a DC voltage to the mag post with a current limiting device like a a headlight bulb and then see if there is magnetic attraction to the first coil core in the frame that the mag post is connected to. If there is magnetism there then there has to be DC current there and the theory of the shorted screw to the rivet is shown to be false. This way nothing gets unsoldered and perhaps not resoldered very well.
The actual DC resistance of the total magneto winding is .25 to .30 ohms typically. I measured 10 of them once for Leo Musch using a constant current and IR voltage drop method with a very accurate DC volt meter. The rest of the resistance is probably coming from the test meter probe leads so .50 ohms is probably legit and about as good as you can measure with an ohm meter. Incidentally all of the coils being wired in series means that each of them should show the same magnetic attraction using a DC current through the mag ring. I wouldn't do that test except you claim to have almost nothing coming out of the magneto AC voltage wise. If you have not actually measured the AC voltage out of the megneto with the car running on battery then you shouldn't be doing any of the testing you are doing. I can't help but fear you are going to put IN more problems than you solve but maybe I am just paranoid.
Oh I forgot to mention that it is often likely to have a short at the barrier strip terminal since the magneto connection at pin 2 of that terminal strip has direct always hot battery power to BOTH terminals 1 and 3 that are on either side of terminal #2. Thus there are two battery connections one on each side of the magneto connection. If the connections there are able to rotate a bit and/or have no insulation on the wire terminals it is rather easy to cause a short from 1 to 2 or 2 to 3 and either one will do evil to your magneto.
Measuring resistance seems to be the logical thing to do but the very low resistances involved provides little guidance as to what or where the problem is.
Has anyone tried measuring the Magneto Inductance to assess magneto coil health? Each magneto coil should have a specific value of inductance. Inductance in series add so a "standard" magneto coil should have 16 x the standard individual magneto coil inductance. If the total inductance is lower, you can calculate which number coil the problem occurs by dividing (the total value measured)/(standard individual coil value). If the total inductance value is correct for the particular year magneto coil, there is no damage indicated and only needs to be recharged.
I say "standard" because I don't know how well magneto coil inductance varies; coil to coil. I know there are differences between years (like the double stack magneto). Anyone ever taken any inductance data or try to characterize different year magneto coils? I tried to do exactly that with help from one of the coil rebuilders but was told; no thanks.....
(Message edited by mkossor on August 17, 2016)
I agree Johns method of discovering if the contact screw is grounding to the frame is a much better approach than unsoldering the button. BTW, John, what is a barrier strip terminal?
I will check the switch but it is a Ben Martin rebuild and is just a year old. I also like your suggestion John as I was nervous about fooling with the solder connection. I am not sure I understand the part about the barrier strip terminal however. I think that I took a reading with the car running using the AC scale but now I am starting to wonder about that since it was almost a week ago and while I know that the output is AC voltage I can't swear that I had the meter set correctly. The only way that I can test again is to button up the hogs head and start the car. I think I will charge the magnets and do that if you think that doing any of the other tests can cause more harm than good. I assume however that I can perform your test John for the mounting screw short without causing any more problems.
Richard and Val,
From what I make of John's post I am quite sure that the "barrier strip terminal" he speaks of is the terminal block on the firewall. The magneto connection (#2) is surrounded by six volts (#1 and #3). Yikes!
Thus the importance of good insulation and tight screws (or nuts and bolts if that is the case).
Bill, I never thought of that as a possible issue. Worth looking into and I know the one on my car is original.
How does one check inductance of a coil/coils? (I'm not an EE.)
What should the expected inductance be? How would you isolate the individual coils? If the car was running and suddenly died why would the coils be suspect? It seems like the focus would be on the magnets if the overall coil resistance is low, as expected. If it was a new magneto with strong magnets and suspect inductance values, and if the resistance was low and continuity is good, would the inductance of a poorly wound coil keep the magneto from producing? In my head (lord help us) the inductance would be affected by the number of windings, the properties of the iron core, quality of material used for the windings, etc.
It seems the direction in his case would be to start with; measuring the resistance/continuity of the coil, then the strength of the magnets. Then if the magnets are weak, determine what caused their failure and correct it. We have an expected value for the strength of the magnets, we have an expected value for the resistance, we have expected output values for the magneto. If any of those aren't where expected, determine what killed the thing and fix it. Fix it means correct the "magneto killer" then recharge the magnets. Was the failure caused by the contact strip? The switch? The battery wire falling off and hitting the mag post? The misalignment of the planets? Sorcery?
My earlier posts focused on a method for measuring the strength of the magnets in expected gauss values. And that would pinpoint individual or overall magnetic strength of the magnets. However, as in inductance, unless the magnets are new, why look for individual suspect magnets? Even with a broken magnet the magneto will probably function.
You really don't understand Mike's suggestion.
The coil ring is made up of 16 individual coils, connected to each other. The end of the "first" coil is connected to the terminal post, the end of the "last" coil is connected to ground. Those two endpoints, and all the coils in between, form a complete circuit. The cumulative windings of all 16 coils have a certain inductance value. If you know approximately what the inductance of a single coil is, and your total inductance reading is lower than expected, you can estimate just which of the 16 coils is shorted to ground. For instance, if the inductance reading was only half what you would expect to see, then probably the 8th coil is shorted to ground, effectively giving you half the coil output you might expect. That would mimic a "weak magnets" condition, when in fact, the coil ring is the problem.
Why not just use a resistance reading? You could, but, since the resistance is very low anyway, a short, at say the 8th coil, would only be reflected by a very small difference in an already very low number. The difference may not even be outside the nominal accuracy of the ohmmeter being used. In short, (no pun), you would have no definite, glaring error with which to form a diagnosis.
If I too am misinformed on his intentions perhaps Mike K. will correct me.
Basically what your saying is everything from the eighth coil to the last contact would show no cumulative value because they're hooked in series. Have I got it? By now you're probably aware you're closer to being an EE than I ever hoped to be.
Yup, that's what I'm saying. Let's see if Mike K. agrees.
Jerry, you summarized my proposed approach very well. To be a successful troubleshooting aid, there has to be a standard inductance associated with each individual coil or at least a way of chacterizing specific year coils so the total inductance measurement value would have a predictable value every time. That means characterizing many coils from many years to see if they are consistent enough to put into distinct bins. That is what I had hoped to do with the assistance from a magneto coil re-builder with access to many coils from many different years; but they said no can do.
Some high end Digital Multimeters have an inductance function. There are also dedicated inductance meters. I would consider designing a simple one for the specific application.
Mike and Jerry, I think you've got me on the way to understanding now. At any rate I've got the MTFCA electrical systems book out and I'm looking at it. I'm having a bit of a problem understanding the way the coils are wound and what happens when the North Pole goes by a coil while a South Pole goes by a coil but it's only because I'm trying to picture in my mind if the oscilloscope would show a double sine wave. I'm looking at it as two different circuits hooked up to a common contact because one set of 8 coils lays one way and the other set seems "upside down"
I gotta say thanks for your patience. I didn't get up this morning thinking I'd regress 50 years and go back to middle school.
Now I'll read my electrical systems book, then go out and Put a coil ring on top of a flywheel full of magnets, spin one or the other and get a vision of what's taking place and properly confuse myself. Thank goodness for the stroboscope because if I had an HCCT I'd be tempted to tear it down and try to understand it.
I think you need to look for a piece of trash somewhere shorting your magneto. Then look for a broken connection maybe at or near the mag post. I would do a lot of detective work before I did an in car recharge. My guess is that your magnets are fine and your problem is somewhere else.
Other than pulling the engine how can you see what is going on at the bottom of the coil ring. I can clearly see that there is no junk anywhere on the top half and I can check all the magnets by rotating the flywheel but even with a mirror I can't get a decent look at the coils on the bottom half. Same is true for a broken connection. All I do know is that the magnets are so weak that even a metal backed inspection mirror is not attracted forcefully enough to the magnets to keep me from getting it down as far as it will fit (but not far enough) and that ain't right.
Val, I think you've got it figured out. There's a lot of theorizing going on here but you're the only one within touching distance of the problem. If you think recharging the magnets is the way to go, it really appears to me you should do an in-car recharge, put the hogs head back on and see where ya sit. Trying to second guess a mag ring with low resistance tells you a lot about the quality of the ring. It doesn't cover all parameters but it should be a pretty good indication that the mag coil ring will work. I guess it's my opinion that's good enough to tell me what the next step would be. What if you do the recharge and it doesn't work, the only time you've wasted is the time it takes you to put the hogs head back on and find out. And if it turns out it is the mag coil ring, then start looking toward pulling the engine.
Just waiting to line up the batteries I need! Hopefully by the end of the week. The suspense is killing me!
In my previous post (I just went back and read what I wrote), I talked about a common contact for two circuits and a double sine wave on the oscilloscope. Then over the last couple hours I sobered up, realized why they were turning the coil windings right hand then left hand to hook them in series and life became less confusing. Now the headache is starting to subside and my vision is becoming a little more clear and I realize how confused I tried to make all this. I also saw an article on the web that showed an example of the sine wave established on an oscilloscope. Very interesting read. Now I have two questions;
1. In the MTFCA handbook I believe I'm reading that it works to "burn-off" shorts in the coil (in-car) by applying the voltage from the recharging batteries to the contact for 30 seconds. This seems a bit extreme to me, is it?
2. Last Winter I pulled the copper coils off a couple magneto coil rings, scrunched them up into an ugly lookin ball and threw them in a bucket of loose copper. Should I have been more careful with how I handled the strips of copper because of the difficulty involved in finding 1/4" copper strips to wind coils with?
I think the inductance value would depend on the rotational position of the flywheel.
If I am correct, then measuring the inductance would be tricky.
Tony, I agree but thought that variable could be managed by orienting the magnets in between coils to minimize effect on total coil inductance measurement.
Michael, we rewind field coils using all new copper ribbon, so yours can still be rewound if you want. The only thing is, the scrap value of the copper is figured into the purchase price, so we'd have to add a few bucks for that.
RV, thanks. I didn't want to throw something away then find out it's not available.
A friend of mine downloaded an app on his IPad for a tesla meter and held it by the magnets in my car. The reading was bit over 120, whatever that means. If that is 120 gauss I assume my magnets are less than half of the minimal requirement for an operative magneto. I don't know how accurate the app is but it was interesting to see how it worked and I assume it clearly shows that the magnets are not strong enough to operate the magneto even if it doesn't help explain what caused them to lose magnetism in the first place.
Val, you did not mention the actual gap between the magnet pole piece and the coil ring pickup.
The first one I did, I thought the important detail was to be sure those pieces did not touch and went for the .040 number.
I had about 6 volts at a high RPM and no Mag at all.
1tesla = 10000 gauss
120 tesla = 1,200,000 gauss
You might could wanna look at that meter and its scale just a bit closer.
Michael, frankly I have no idea what he was doing but I think he said the scale was micro tesla or milli gauss, I don't remember which. I am way over my head here! All I know is I was putting out near 30 volts one minute and had a dead mag the next. Gap was set at a tad over .025 a little over a year ago when the engine was rebuilt, that is what it is now and there is no end play.
Val, check it out!
One of my fears has been losing my ability to run on mag. It actually happened on my touring car about 5 years ago. I had too much crankshaft end play. I had the thrust rebuilt on the rear main bearing and that got me through for a year or two.
Anyway, since I started following this thread I've gained a lot of knowledge and feel comfortable I would be able to re-magnetize the magnets in my car if I needed to.
The above website seems really easy to follow and like you I'd pull the hogshead off and then follow the method shown in the site.
I think a guy could use a fishscale rigged to check the "pull" in lbs to check the magnets. I've got a big old Napa battery charge that I can adjust the current on and I don't think it would take much to do the job.
Please keep us informed of your progress.
Michael, I have done in car magnet charges on T's many times over the years with great success if the gap is acceptable and the mag coil is good. I have also used an accessory shim behind the crank pulley as a temporary fix for end play and replaced the third main for a more permanent fix but in each of those case the mag simply got weaker and weaker over time. Here the mag was working fine and just died completely.
The problem with trying to read the inductance is that you have very little access to any but the top coils with the mag ring in the car. This is also a problem with applying DC current and testing each coil "core" for magnetic attraction while the ring is in the car and on the motor. My DC test was simply to verify the issue with the connector block rivet shorting out. Whether you measure inductance or magnetic attraction - you probably need the motor apart and then the DC test is pretty reliable and simple in spotting which coil(s) are bad or shorted. The fix is generally the same - a new rebuilt Field Coil. If there was a reliable way to fix a defective field coil while it is still in the car then a fancy tester would be worth the money.
John, Thanks for your comments on measuring magneto coil inductance. I agree defective coils would require removal and replacement. Also agree that applying a DC current to the coil and using the magnetic attraction test to locate the defective coil(s) is simpler, accurate and low cost.
I suppose the only benefit of a magneto coil inductance test (if one could be established) would be to determine if the magneto coil was not damaged and an in car magnet recharge of potential benefit. Probably not worth the effort to design a dedicated magneto coil inductance tester.
I see a lot of talk and not too much in the way of action. Val if I had your problem I would be looking at the coil box for a bad switch or a wire shorted to another wire. The only way the magnets can lose their magnetism suddenly would be for DC voltage to be applied to the MAG post with the car running.
This would not be caused by any problem inside the engine. At this point you should try an in car recharge, then measure MAG output with the engine running on battery but the MAG post wire disconnected.
Another easy test that you can try would be to disconnect the wire from the MAG post and measure to see if battery voltage is present at any key position.
Royce that has been my suspicion from the beginning but I pulled the hogs head because I had rebuilt one with new shafts and cams a while ago to replace the one on the car. I figured now it would be a good time to do that since it would also permit me to inspect the mag ring and magnets at the same time. I am still trying to line up the 3 batteries and connecting cables to do the in car charge.
Val, before you put the hogs head back on line the magnets up in the proper position with the coils so you know you'll be zapping the magnets right. If the magnets are really weak the compass might not definitively show which magnets are north and which are south.
I plan to zap the magnets with the hogs head off first and have already marked the magnets with a grease pencil. I have done it this way before with great success. I am hoping that it works again this time and that there are no other issues.