Sudden Magneto Failure

[paddy1998]

I was driving my 22/23 Touring (26 engine) on magneto and everything was going swimmingly at 41 mph on smooth pavement when all of a sudden it just died. No clanging, no strange noises, no sputtering, just dead same as if I switched it off. I put the pedal in neutral and rolled to a stop.

No looses wires, nothing apparently broken. Starts and runs fine on battery.

I checked the switch (I use a SPDT toggle switch) and it's working fine. The magneto post is 3 months old (outside oil line type) and isn't broken. When I removed it to check, it was as clean as the day I installed it. No debris, band material, or anything else was on it save a film of motor oil.

Anything else it could be, other than a short in the field coils? Have I missed anything obvious?

I really don't think my magnets need recharging because right up to the moment this happened it ran better on magneto than on battery. At least it seemed that way.

[TXGOAT2]

I would re-check every connection. It's probable that you have a loose connection, and I would suspect the mag post, even if it's new. Also check the dashboard switch and all connections to it. If you have an AC voltmeter, check for voltage at the mag post with the engine running at fast idle. Connect test leads to the mag post terminal and to a clean engine ground. I would not use the exhaust manifold as a ground point. Scrape a small spot on the block clean, if necessary.

[R.V.Anderson]

Awhile back, several folks experienced just what you did, and the trouble was traced to the new mag post oilers which were grounding the magnetos. That could be your trouble, but it could also be that a bit of wire was picked up by the magnets and jabbed into the field coil. That happened to my '14; the culprit was a broken clutch finger cotter pin. From what you describe it doesn't sound like a loose solder joint in the field coil; when that is the issue you usually get some spitting and backfiring, and even brief periods of normal running, before the magneto entirely dies. You state that the mag post contact is clean, but take a good hard look all around the contact solder button with a mirror and a good light. You may find a wire or the like around it, grounding out the whole works. It happens fairly often.

[Oldav8tor]

Photo of the mag post might help. My friend had one modified for an oil line that stopped working. Upon inspection I believe the internal insulation failed allowing it to short out. A new mag post and he was back in business.

[RustyFords]

If it were mine, I'd put the old, non-oiler, mag post back on and see if that cures the problem.

[Norman Kling]

On one of my T's right after I installed a rebuilt engine, the first time I drove it, I was running on magneto and all of a sudden it quit. It ran fine on battery and I drove it on battery for about 10 years. Then, I rewound several magneto coils when I was working on another T and decided to put one in the T I had been driving. I pulled it out and found the funnel from the oil line had come off and laying in the bottom of the crankcase. It had cut the coil ring when that happened. Must have been too close to the magnets when the engine had been rebuilt. Fortunately I did have the magneto oiler on that engine and it ran for many years without an engine problem.
If you pull out your magneto plug and put a probe of an ohmmeter on the button at the top of the magneto ring, you should read ground. It could be grounded somewhere else in the ring, however, it reads open, you know the ring is no good. If you read ground, you can check the plug or replace it with another and it might work fine. I have found that some of the oiler plugs don't have a long enough contact and sometimes it can be fixed by adding one or more small washers on the underside or by adding a bit of solder to the end of the contact.
Norm

[speedytinc]

If it were mine, I'd put the old, non-oiler, mag post back on and see if that cures the problem.

Did you do a meter test? Any running output? Continuity? Could you have gotten some DC to it? Loose wire, wedding ring short?
Further testing & trials needed.

[Bill Dizer]

Timing gear?

[speedytinc]

Timing gear?

You may have missed that it runs fine on battery.

[paddy1998]

Thank you all for the advice.

Today I got around to going down to Menards to get an analog multimeter.

I'm getting 2 VAC at the magneto post at high idle, slightly more with higher rpm.

I guess it's the magnets, huh?

I suppose the next step is an in-car recharge of the magnets.

I really wish this kind of thing would happen in May, instead of November when I have to wear pants.

[speedytinc]

Thank you all for the advice.

Today I got around to going down to Menards to get an analog multimeter.

I'm getting 2 VAC at the magneto post at high idle, slightly more with higher rpm.

I guess it's the magnets, huh?

I suppose the next step is an in-car recharge of the magnets.

I really wish this kind of thing would happen in May, instead of November when I have to wear pants.

Your assessment smells right. DC killed the magnets.
Figure out how it happened & dont do it again, assuming the recharge gets you back to 30V.

[Norman Kling]

Try this. Push down the clutch then release it. Go to the front of the engine and with a very large screw driver or pry bar, try to push the crankcase pulley forward. Pry against the front of the engine but not hard enough to bend anything. If the crankshaft moves forward, your problem is that the magnets have moved away from the coils. In that case, you need to build up the thrust surface on the rear main bearing. If you have a 4 dip crankcase, it can be removed with difficulty from under the engine. You must put rags down the back of the crankcase next to the magneto coils so that you won't drop anything down. Then build up the babbit on the front side of the cap and trim to fit. With the two dip crankcase you need to pull the engine to do this. And it is much easier to do it on the 4 dip crankcase if you pull the engine. Some have tried a spacer between the front of the engine and the pulley. I have never tried it this way, but it is a stopgap until you need to pull the engine for some other reason. Or else you can just run on battery until you need to pull the engine. It will run fine but not have quite as much power as on magneto.

If you don't have end play in the crankshaft, then you can try the in car recharge.
Norm

[Scott_Conger]

Nope>

Next step is to find out why battery voltage got to the magnets, if the magnets are in fact discharged. A sudden failure and puny output is a classic battery-to-mag ring short.

didn't you just go through this recently? I seem to recall you had a switch failure and went to fool-proof toggle switches and already recharged the magnets

Myself, I'd suspect that something is grounding or providing a partial path to ground in the magneto post. That would provide for a sudden loss of juice and a puny output if there is a low-resistance ground

[TXGOAT2]

I'd look very closely at the mag post. Not all failures are total. You could still have a short at the mag post or a poor connection there. Also: It may be possible to access the magnets thru the transmission cover plate. If it is possible... ///// ****It's not. The starter would have to be removed.***////// ....you might try using something like a 1/2" mild steel rod to check for magnetism by bringing the end of the rod into contact with the outer ends of the magnets where they come close together. If you try this, use a rod that is too long to have any chance of falling into the transmission. Mild steel rods are available at TSC and Lowe's, etc in 3 foot lengths.

[paddy1998]

Nope>

Next step is to find out why battery voltage got to the magnets, if the magnets are in fact discharged. A sudden failure and puny output is a classic battery-to-mag ring short.

didn't you just go through this recently? I seem to recall you had a switch failure and went to fool-proof toggle switches and already recharged the magnets

Myself, I'd suspect that something is grounding or providing a partial path to ground in the magneto post. That would provide for a sudden loss of juice and a puny output if there is a low-resistance ground

No, I haven't had this happen before. Someone else did, which was why I was able to check a bunch of stuff before posting.

I did replace my switch assembly with toggle switches in August and it's been running fine since then. I checked the continuity at the switch and there is no continuity between the battery side and the magneto side regardless of switch position. The magneto side of the switch is isolated.

What other ways could DC be getting to the magneto?

[Scott_Conger]

What other ways could DC be getting to the magneto?

None

that's why Pat and I both are telling you to look at your mag post and verify good electrical isolation...as in: remove it and check it electrically for complete isolation to ground between the output post and the mounting flange

Loss of mag is often due to careless farting around with wiring, or a switch failure sending DC through the coil and killing the magnets. You had neither of those happen. This drives the fault not to discharged magnets, but a grounding of the mag ring. Hopefully at the post.

[R.V.Anderson]

What Scott said. While you could certainly have discharged magnets, it's at least equally likely that you have a grounded or shorted field coil. As I posted earlier, the same thing happened to my newly rebuilt '14. I too got only 2 volts at idle when it happened. Hopefully it is the magnets, and you can do an in-car recharge after eliminating the source of the DC voltage leak. If it's a damaged field coil you will have to pull the engine to effect a repair.

[paddy1998]

What other ways could DC be getting to the magneto?

None

that's why Pat and I both are telling you to look at your mag post and verify good electrical isolation...as in: remove it and check it electrically for complete isolation to ground between the output post and the mounting flange

Loss of mag is often due to careless farting around with wiring, or a switch failure sending DC through the coil and killing the magnets. You had neither of those happen. This drives the fault not to discharged magnets, but a grounding of the mag ring. Hopefully at the post.

Thanks. I'll check for ground at the post/mount.

[speedytinc]

If the magnets are not discharged, running a compass around the HH would quickly confirm it with strong needle fluctuation.
Zero movement, another story.

[paddy1998]

Yep, the post is grounded. Can't figure out why though. It shouldn't be, but it is.

They're cheap so I'm just going to order a new one and see if that takes care of it.

A thought has occurred to me as I write this. The post is grounded to the post housing when screwed into the hogshead, but the post is not grounded to the post housing when not screwed into the hogshead.

Strange. I get the feeling that I'm missing something.

[Scott_Conger]

Yes, the post is grounded when installed...it is grounded through the mag ring (you're measuring the continuity of the windings). If you "zero" out your test leads first, you'll find (I recall) about .3 OHM resistance through the winding.

If the continuity is "0" ohms when installed, then the post is in fact grounding to it's base...there is a difference

[TXGOAT2]

I've had the newest part on a car fail more than once.

[paddy1998]

For reasons I cannot understand my magneto is working fine again.

I didn't do anything at all. Today I got around to checking the resistance at the post and it almost buried the needle. I thought I was doing something wrong until I looked harder at the meter (I haven't used an analog multi meter since I was in grade school) and saw it was registering less than 1 ohm. Can't say exactly what it was because I forgot my cheaters in the house

For the hell of it, I started the engine and measured the volts at the post again. Previously it had been 2 VAC at high idle and nominally more at higher rpm.

Tonight it was putting out 8-10 VAC at high idle. I switched to magneto and the engine continued to run as normal, as though there had never been a problem.

I swear I did absolutely NOTHING other than drive it about 10 miles on battery.

This is some kind of witchcraft!

[Scott_Conger]

Now, aren't you glad you didn't go about recharging magnets?

Sounds like you have or had an intermittent short in the mag post. If it happens again, at least you won't wig out and should have a plan of action already to go.