MTFCA Forum

I’m looking into why the magneto isn’t working on my ‘26. I’ve checked the post and it was fine. I just now checked the endplay and it seemed fairly significant to me. It’s an exaggeration, but I would say it’s nearly 1/8”. That’s just a guess. The black book talks about an oversized bearing endcap. Do they still make those? Lang’s only shows a crankshaft shim that I suppose goes on the outside of the engine and might need to be machined. I don’t have a way to do that.

By "dosent work" you mean 0 output? That's not an end play problem. A wide magnet gap would mean weaker output.
With the clutch disengaged, you would have a reasonable output.
A 3rd bearing cap fitted with the correct thrust would be the fix for excessive fore & aft crank movement. Ready to pull the motor to replace that 3rd main? Whall your motor is apart, you can replace the field coil (presumably) with a good one & recharge the magnets etc. to get your magneto working again.

The Langs Brass shim goes behind the pulley. It is attached by the 2 bolts on either side of the crank front timing gear cover.
The mount is slotted. If some material is needed removing, it can be done with a file or sanding disk.

I have used the pulley shim on one of my cars for years with great success. It was a good temporary fix that kept the magneto functioning until the engine finally got to the point where I pulled it for a total rebuild.

I guess I assumed from the Black Book that if there was too much space the magneto wouldn’t work at all. I know I’ve not gotten a light to work by hooking it up to the post and when I flip it over to ‘MAG’ it immediately dies.

Russ T Fender wrote: ↑

Thu Feb 12, 2026 6:42 pm

I have used the pulley shim on one of my cars for years with great success. It was a good temporary fix that kept the magneto functioning until the engine finally got to the point where I pulled it for a total rebuild.

Would it be possible for you to post a picture of it installed?

Have you verified that there actually are magnets on your flywheel ? The past 40 years or so, it’s been popular to think a Model T can run 70 mph with modern traffic if only all that unnecessary revolving weight (flywheel magnets, cast iron pistons, etc.) can be eliminated.

How was the 1/8" end play measured? If it was done by levering on the fan pulley and engine block, some of it could be due to a loose fan pulley. Whatever, 1/8" is excessive. If it is due to wear on the thrust face on the third main, I would suspect that the crankshaft flange is also worn. That rules out re-working just the bearing thrust face. The crankshaft flange would need to be ground and trued for a new third main cap to be made to suit.

Allan from down under.

Rich P. Bingham wrote: ↑

Thu Feb 12, 2026 7:52 pm

Have you verified that there actually are magnets on your flywheel ? The past 40 years or so, it’s been popular to think a Model T can run 70 mph with modern traffic if only all that unnecessary revolving weight (flywheel magnets, cast iron pistons, etc.) can be eliminated.

Good point. I hadn’t thought of that.

Allan wrote: ↑

Thu Feb 12, 2026 8:42 pm

How was the 1/8" end play measured? If it was done by levering on the fan pulley and engine block, some of it could be due to a loose fan pulley. Whatever, 1/8" is excessive. If it is due to wear on the thrust face on the third main, I would suspect that the crankshaft flange is also worn. That rules out re-working just the bearing thrust face. The crankshaft flange would need to be ground and trued for a new third main cap to be made to suit.

Allan from down under.

I may have to check again. I had the pry bar between the engine and lower pulley.

Has the magneto ever worked in this car?

I would test the magneto before going too far.
https://www.mtfca.com/discus/messages/5 ... 1470945248

It is possible to have a shorted magneto post so that is a quick test.
The last one I found was a tiny bit of wire caught in the spring, never found out where it came from.
I have seen several mag posts that do not connect well in certain spring positions so check that while you are at it.
There are lots of wiring connections inside the ring coil that can fail.
Magnets can discharge or be broken
The wiring up through the switch can fail
Parts can be missing

While crankshaft end play should be addressed it may not be something to fix today.
Sometimes you wait until there is another reason to have the engine out.

Main Bearing Caps:
Langs no longer carries re-babbitted caps. You have to get them from your favorite babbitt shop or Rons Machine https://www.facebook.com/RonsMachineShop/
The thrust is always made oversize and has to be hand fitted.
The diameter is cut to several undersize values but needs to be final fitted to your crankshaft.
They are not drop in parts.

Crankshaft End Play Shim - 3030SHIM:
This is also oversize and needs to be cut to fit.
It will take multiple attempts to get it right.
The only one I ever installed was not in there long.
It was in there long enough for me to find out the engine was totally worn out and needed rebuilding anyway.

Find all the problems and then determine the way you want to fix your car.
Sometimes it's run on battery until it's time to fix it "right".
Mike

It amazes me that even after 100 years bandaids for Model Ts still sell.

Dan

Band-Aids still sell because surgery is expensive!

Mike Silbert wrote: ↑

Thu Feb 12, 2026 9:02 pm

Has the magneto ever worked in this car?

I would test the magneto before going too far.
https://www.mtfca.com/discus/messages/5 ... 1470945248

It is possible to have a shorted magneto post so that is a quick test.
The last one I found was a tiny bit of wire caught in the spring, never found out where it came from.
I have seen several mag posts that do not connect well in certain spring positions so check that while you are at it.
There are lots of wiring connections inside the ring coil that can fail.
Magnets can discharge or be broken
The wiring up through the switch can fail
Parts can be missing

While crankshaft end play should be addressed it may not be something to fix today.
Sometimes you wait until there is another reason to have the engine out.

Main Bearing Caps:
Langs no longer carries re-babbitted caps. You have to get them from your favorite babbitt shop or Rons Machine https://www.facebook.com/RonsMachineShop/
The thrust is always made oversize and has to be hand fitted.
The diameter is cut to several undersize values but needs to be final fitted to your crankshaft.
They are not drop in parts.

Crankshaft End Play Shim - 3030SHIM:
This is also oversize and needs to be cut to fit.
It will take multiple attempts to get it right.
The only one I ever installed was not in there long.
It was in there long enough for me to find out the engine was totally worn out and needed rebuilding anyway.

Find all the problems and then determine the way you want to fix your car.
Sometimes it's run on battery until it's time to fix it "right".
Mike

I actually thought it did when I first got it, but if so it was brief.

Possibly a really dumb question. It’s an early spring in Iowa so I’m out tinkering on the T and getting sun. I thought I would check the continuity from the MAG post to the other end that goes on the terminal block. I haven’t disconnected any wires, but so far I have continuity from the post to ANY wire on the terminal block. Is that correct? Doesn’t seem like it.

Here is a real good possibility- if you or someone else has done some electrical repairs...or testing.... on the vehicle's electrical system, and somehow, either knowingly or accidently allowed DC current to enter the flywheel and/or magnets (or mag post) a bad mistake has been made. DC current entering the magneto system (even slightly) will KILL the magnetism of the flywheel magnets-- and it only takes a slight flash. The magnets can be re-magnetized but you will need the Black Book for info. Better yet- contact your local Model T Club.

Your club might have a Magneto University that you can attend, like our club had when we were young. See the photo.

When the magneto wire is hooked up it is grounded on the other end and has low resistance.
The lighting circuits (3 of the screws) will have low resistance bulbs also connected to ground. This might show up as a short with two low resistance parts in series. Incandescent bulbs are low resistance and LED's are high resistance and polarized.
That leaves the Battery terminal and Generator terminal.
I am racking my brain on these two circuits but I can not find a definitive answer.
There are multiple different cutouts and regulators and some might pass power back through maybe.
The battery terminal could sense through the battery causing a false reading maybe.
There is also the world of different types, makes and models of meters that could be used to get the reading adding another variable.
Back feeding does weird stuff. Think about what happens when a multiple bulb fixture looses it's ground.

This is an example of why it important to isolate circuits when testing resistance.
The magneto resistance should be about 1/2 ohm so it will look like a dead short.
If the magneto post is shorted it is hard to meter read since 1/2 ohm is about the same as 0 ohm to most meters.

I will reiterate that if the wiring was shorted with a quick flash it will discharge the magnets and "kill" the magneto.
The magnets can be recharged in the car, if you follow the correct procedure.

As with most everything the devil (and problem) is buried in the details.
I don't think testing / checking is done yet.
Mike

Is the way the junction block wired on page 43 of the Black Book the way all years are supposed to be? Mine is wired up a little differently.

Not all Model T's are wired the same
See
https://mtfca.com/phpBB3/viewtopic.php?t=2960
https://nebula.wsimg.com/bfee1cac0d0763 ... oworigin=1
and I use
https://www.texastparts.com/mm5/merchan ... ory_Code=z

Everyone has their favorite drawing and accessories are custom wired.
I'm sure others will send their favorite wiring diagrams also.
Mike

I checked a brand new ignition switch that I have, but haven’t installed. I got completely different readings with the continuity meter. Checking the old switch (new not original) I can put one lead on the ‘BAT’ and the other on any one of the other screws and I have continuity from. That doesn’t seem right, does it? The new switch doesn’t do that.

Mike Silbert:

This is an example of why it important to isolate circuits when testing resistance.

I very much suspect that your new switch is laying on a bench and has nothing connected to it and thus checks out correctly

Similarly, I very much suspect that your old switch is still in the car and is connected to wiring of unknown condition or correctness

If my suspicions are correct, then refer back to the quote from Mike Silbert - meaning that as a start, each individual circuit at a very minimum, needs to be checked for isolation and ground

Scott_Conger wrote: ↑

Sun Feb 15, 2026 4:16 pm

Mike Silbert:

This is an example of why it important to isolate circuits when testing resistance.

I very much suspect that your new switch is laying on a bench and has nothing connected to it and thus checks out correctly

Similarly, I very much suspect that your old switch is still in the car and is connected to wiring of unknown condition or correctness

If my suspicions are correct, then refer back to the quote from Mike Silbert - meaning that as a start, each individual circuit at a very minimum, needs to be checked for isolation and ground

That is the way I’m currently testing it. I will try it the proper way next.

I took the wires off the switch and tested it. It tested fine and normal. I am going to replace it as it turned so hard that it feels like the key will twist off. I’m not sure what to test next. Everything (except the magneto) works as it should. Lights go on and off as normal.

Model T switch tumblers were made from pot metal that often swells and gives problems after the last 100 years.
Add a bit of rust on the steel parts and it gets stiff.
Careful lubrication and working it can sometimes bring it back around, be careful not to break it.

If the tumbler does need replacing it is not a quick / easy job but possible.
And watch out, the replacement tumblers don't just drop in and need some rework for a proper install.

No matter what you do having a good functioning switch is important to reliable operation.

While it is apart, check the continuity of the magneto contact (inside the hoggs head hole) to ground and cleanliness/conductivity of the magneto post.
It unscrews from the top of the hoggs head to get in there.
That will tell you if there is a chance of life in the magneto.
Mike

I pulled the magneto post yesterday. I’ve had it off before. It was clean and had continuity. I tried putting a scope in the top of the transmission to see if the magneto is actually there, but it was inconclusive. It’s really not visible unless you take the hogshead off, I assume?

With apologies: I misread an earlier post and gave poor advice due to that, and have now removed my advice due to it being erroneous

CatGuy wrote: ↑

Thu Feb 19, 2026 2:54 pm

I pulled the magneto post yesterday. I’ve had it off before. It was clean and had continuity. I tried putting a scope in the top of the transmission to see if the magneto is actually there, but it was inconclusive. It’s really not visible unless you take the hogshead off, I assume?

When you remove the mag post, you would see a lead button that the post spike contacts. It's centered in the hole & not very deep.
When you put the mag post back you will have to push it down on the lead button, compressing the spring.
Its obvious if there is a field coil or not. If you can push your scope down thru the mag post hole, there is no field coil.

This following discussion shows a lot of pictures of what the magneto looks like inside
https://www.mtfca.com/discus/messages/1 ... 1264263362

Here is a Borrowed picture from the post above

speedytinc wrote: ↑

Thu Feb 19, 2026 3:39 pm

CatGuy wrote: ↑

Thu Feb 19, 2026 2:54 pm

I pulled the magneto post yesterday. I’ve had it off before. It was clean and had continuity. I tried putting a scope in the top of the transmission to see if the magneto is actually there, but it was inconclusive. It’s really not visible unless you take the hogshead off, I assume?

When you remove the mag post, you would see a lead button that the post spike contacts. It's centered in the hole & not very deep.
When you put the mag post back you will have to push it down on the lead button, compressing the spring.
Its obvious if there is a field coil or not. If you can push your scope down thru the mag post hole, there is no field coil.

I definitely saw that button. I couldn’t get much farther with the scope. So, I at least have a Mag….of sorts.

You can see it better with the top cover - the one above the bands - removed.
That's also the place to look to align the magnets for re-magnetising.

Honestly, if the crankshaft has 1/8" of play, or anywhere near that, the Magneto is not going to power the car, so any time poking around looking for magnets could really be put to better use drinking beer.

The Forum has a great propensity to typically send you down rabbit holes by the time there are 6 postings or so. At some point someone is going to ask if you've checked the rear end for babbit washers and at that point you know the thread ran its course several weeks prior.

Nice weather is on its way, so suppress the urge to poke around and start enjoying the car - magnets or not, the fix to your problem is either expensive or labor intensive (and sometimes both), so just Put the new switch in, drive it on battery.

If there was really 1/8" play, wouldn't the magnet keepers have already crashed into the field coil?

I'd think so.

If wear must always be TOWARDS the coil ring and it MUST therefore crash, then why exactly would a shim between the front of the block and the back of the fan pulley pulling the magnets closer to the mag coil be such a successful fix for the last 110+ years?

The answer is, of course, despite the fact that wear SOMETIMES causes magnets to rub the mag ring, SOMETIMES it doesn't. And that SOMETIMES happens so frequently that there is a solution to that particular problem that has been around for 110+ years.

BTW, I seriously doubt that there is 1/8" play...movement that can be witnessed by eye - excessive, 1/8", probably not.

When the clutch is held in neutral, doesn't that pull the crankshaft and flywheel toward the back of the car, and away from the coil ring? When the clutch is engaged, which it normally is, isn't the crankshaft free to float forward and back within the thrust bearing clearance? If that's so, I'd expect the balance of thrust face wear to be on the forward thrust face, with very little wear occurring on the rearward thrust face, so the danger of the magnet retainers hitting the coil ring is very low. If I had excess play, I'd buy the inexpensive adjustable shim that goes on the front of the engine, install it loosely, then have someone pry the crankshaft forward to its limit, then set the shim to leave about .005 clearance, tighten everything up, then re-check the clearance. If OK, crank the engine by hand for several revolutions. If no interference, start it up and let it warm up. If OK, then try out the mag.

I completely agree with Pat, above.

You only get wear on the rear face of #3 main which might lessen the magnet clearance when descending a hill in high gear.