MTFCA Forum

Hey all,

I had a hole in my #4 cylinder, and decided to replace the block instead of getting it bored and sleeved to save cost. I have been installing most of my old parts, (including my original crank) along with a few new ones and it has gone surprisingly well with no issues. Until now. I mounted the field coils to the block, and then the flywheel.

When I started torquing down the flywheel, I noticed the engine getting harder to turn like something was getting snagged. Turns out it was the magnets rubbing against the coils. I thought that it was just because I hadn't got all four bolts torqued evenly, and maybe the flywheel just wasn't on straight yet. I decided to keep going.

Well that was a stupid decision, because now the flywheel wont even turn enough to get the remaining 2 bolts out that I could not reach after it jammed.

I really don't want to pull the pistons and crank back out, I am trying to have this car ready for the Virginia city tour in a week or two and I need all the time I can get because the whole car is pretty much apart. I like a good challenge.

Has this happened to anyone before? what would you do about this? any knowledge is much appreciated. Go easy on me, this is my first time putting a motor together. So far I'm having a blast.

Thanks in advance!

Reverse the process that locked it up. The field coil will flex a little. I might try some gentle pry bar application at various spots until I find that spot that allows the flywheel to move. GENTLE prying, dont want to over stress & break the coil casting. Shouldn't take much.
Did you have a shim/s under the field coil? Remove them.
Depending on the machining of the 3rd main, the crank flange can be in wildly different positions.
The field coil can be surfaced @ the mount to give more F/W gap. A shim can be made to go between the crank & F/W.
Its common sense.

If you don’t have the repair manual, at least consult the forum archives. In order for the magneto to function, there is a necessary minimum (.010”) / maximum (.040”) gap between the flywheel magnet clamps and the field coil cores. Obviously, the flywheel needs to turn free of any interference caused by too-close tolerances. An average gap of .025” is ideal.

Here’s the tricky part - the crankshaft will flex .005- .010” , literally sagging with the weight of the flywheel. The manual indicates there is .010” compensation built into the field coil casting. Setting proper clearance is an annoyingly painful process that usually requires removing and replacing the flywheel a few times to get it right. As noted, there are shims available to aid in setting the gap, if yours is binding, remove the appropriate amount of shim stock. Personally, I have never encountered a field coil that would bind without any shims in place, but if that is your situation, then it’s logical the remedy would be to remove material from the field coil mounting flange. Good luck !!

Like Rich says, its an iterative process. You need to have the engine oriented vertically when you do it.

Rich B. Your .010 min is way too close. I don't have a service manual with me, or I would give an accurate quote, but I believe the minimum is .025" When setting the clearance,(vertically) you want .010" more clearance @ the bottom to allow for sag.

John, I shot from the hip. I believe you are correct ! And good you mentioned the engine has to be vertical (as assembled in the car) in order to fit the gap. Very important !

...now the flywheel won't even turn enough to get the remaining 2 bolts out that I could not reach after it jammed. I really don't want to pull the pistons and crank back out...

Can you remove the rear main? If there are no flywheel bolts in the way, you should be able to remove the rear main and the others as well, along with the rod caps. You don't need to actually remove the pistons as you feared you might. This should allow you to lift the crank enough so that it can then be slid back, to relieve the binding.

Then, figure out if you cracked the mag ring casting... and also, why things bound up in the first place. Pictures posted here would be helpful for us all.

Guessing the thrust is gone on the rear cap. There are ways to address that. Try pushing the crank back to the rear and see if that helps get some clearance. Are you installing the flywheel in the horizontal or vertical position? If vertical, swing to horizontal and try that.

Mark Gregush wrote: ↑

Tue Sep 03, 2024 3:59 pm

Guessing the thrust is gone on the rear cap. There are ways to address that. Try pushing the crank back to the rear and see if that helps get some clearance. Are you installing the flywheel in the horizontal or vertical position? If vertical, swing to horizontal and try that.

It isn't that the magnets are just rubbing. He has everything bound up so tight that he can't turn the crankshaft. Being vertical or horizontal won't change a thing. He just needs to get it apart again, but can't turn the crank enough to access all 4 flywheel bolts.

The first time putting a T engine together it helps to use the Ford service manual and getting the necessary knowledge beforehand really helps. To keep from doing some unintentional damage to it you may have to remove all the crankshaft main caps and carefully see if you can lift out the transmission and crankshaft together. That will depend in what position the crankshaft now is. It may not be easy but if you can’t get access to the crankshaft bolts that may be the only way to do it since you now can’t turn the engine over at all. Just don’t bend the crankshaft if you try to do it this way. This isn’t a good way for some folks but it is possible.

I feel for your problem but at the same time, am amused by the fact that people think that a T is just a bolt together project, they are complex and take experience and knowledge to be a successful build, all I do are T's and come across major screw ups done to them, even by modern day mechanics and machine shops.

Unusual! Usually, the rear main will wear in the direction to pull the magnets away from the coils because the clutch tends to push the flywheel forward.
Unfortunately, thrust surfaces of the rear main bearing are bored to fit the crankshaft when the engine is rebuilt. Therefore you are using a block which was machined for a different crankshaft and the thrust surfaces of the rear main were ground to fit a different crankshaft.
With these things in mind the first thing to do is mount the engine nose down so that the crankshaft goes forward as far as it can. Then check the clearance between the flywheel and the magnets. If it is only binding on one side or in top or in bottom, your coil ring is on crooked. If bottom of the coil ring is more than enough clearance than the top you will need to either remove shims from the top of the coil ring or add shims to the bottom of the ring. Adjust the shims until the clearance is the same all the way around. Other times the magnets have not been set so that they are the same distance all the way around the flywheel. So you will need the manual to check all these adjustments and work on it until everything fits. It is also possible you will need to re-babbit the cap to fit the crankshaft to adjust the thrust. If you can find someone in your area with experience, you might be able to get some hands on help. There used to be a chapter of the club in Las Vegas, so you might try there to find help.
Norm

I took off the bottom cap of the third main, slotted the boltholes slightly and reinstalled it when the crankshaft was eased backwards to provide 1/32 inch gap between the windings and the magnets. I don't know why I did that but it worked, I must have read it somewhere but the car now runs well on magneto.

speedytinc wrote: ↑

Tue Sep 03, 2024 2:19 pm

Rich B. Your .010 min is way too close. I don't have a service manual with me, or I would give an accurate quote, but I believe the minimum is .025" When setting the clearance,(vertically) you want .010" more clearance @ the bottom to allow for sag.

Yes, the 0.010 inch is too close, but Wally (the guy that rebuilt coil rings) told me he set his a 0.015 inch. Produces a very strong magneto.

John.Zibell wrote: ↑

Wed Sep 04, 2024 8:35 am

speedytinc wrote: ↑

Tue Sep 03, 2024 2:19 pm

Rich B. Your .010 min is way too close. I don't have a service manual with me, or I would give an accurate quote, but I believe the minimum is .025" When setting the clearance,(vertically) you want .010" more clearance @ the bottom to allow for sag.

Yes, the 0.010 inch is too close, but Wally (the guy that rebuilt coil rings) told me he set his a 0.015 inch. Produces a very strong magneto.

YIKES!
You cant go wrong following the service manual.
.015" clearance leaves no room for wear or transmission sag.
This is a potentially catastrophically dangerous unnecessary practice
A good magnet charge will produce 35 volts output @ book specs. Thats plenty for easy 1/4 turn pulls on mag while also charging a battery.
Also there is Horse power loss from excessive magnetic pull.

Follow the recommended gap instruction in the manual and you’ll be fine. Over the years folks have gotten a really close average setting but .025 is right overall I think. I set my cars that way and they run fine when switched to mag.
Setting the mag gap takes time and patience and it isn’t just a quick bolt up. And remember to check for the sag when you turn your engine to horizontal on the engine stand.
That’s when you add shims to level the gap out when you’re trying to get the same clearance all the way around. Take your time and you can make it happen.

Thank you for the knowledge. I figured out my problem, should have posted pics cause you guys would have immediately seen my issue

I originally put the flywheel on so I could turn the motor over to adjust my new tappets, and that's when It jammed. I didn't take the motor apart originally, and I haven't seen one of these apart before. I ordered the green Ford transmission book and found out I was supposed to install the transmission shaft before the flywheel

Didn't think I had to read through that just to install the flywheel. I guess I learned a good lesson.

I put the shaft on and then the flywheel and had quite the opposite problem, I had about a 75 thousands clearance between the ring and magnets.

I cut up a redbull can I drank an hour earlier, and folded it over a few times. It happened to be exactly .040 thick when completely flat, so I made a few shims. It's got just barley more than .025 now (my feeler doesn't go bigger than that)
Thanks again for the help, I hope I'll see you at the Virginia City tour. I'll be the exited teenager in the 24 touring!

I assume you are using BRASS feeler gauges ??? Steel will give you an erroneous reading.

RajoRacer wrote: ↑

Wed Sep 04, 2024 11:05 pm

I assume you are using BRASS feeler gauges ??? Steel will give you an erroneous reading.

How could that be?

The magnetizim creates a false friction, so you feel a friction like the gap is correct, but there is still a gap on the non magnetic side.
You can overcome this by adding more thickness (another leaf) feeling for the added friction of a correct reading.
The process is easier/more fool proof with brass feeler gauges.

Spot on John!

Hope you have not forgotten about the safety wire.

Absolutely yes as Dan H. advised! Don’t forget to use the safety wire. That’s what the holes are for in the bolts that hold on the mag ring.
Also check to make sure that the oil funnel has good clearance so it won’t hit the flywheel. Make sure it’s flush against the mag ring or as close as it will go.

Mr man wrote: ↑

Wed Sep 04, 2024 11:00 pm

I cut up a redbull can I drank an hour earlier, and folded it over a few times. It happened to be exactly .040 thick when completely flat, so I made a few shims. It's got just barely more than .025 now (my feeler doesn't go bigger than that)


Thanks again for the help, I hope I'll see you at the Virginia City tour. I'll be the exited teenager in the 24 touring!

I guess the RedBull can will work, but just so you know, the suppliers sell the proper shims for this. They have a small tab that is meant to stick up and act as "fingers" to hold the hogshead felt seal in place during assembly, so it can't slip back.

https://www.modeltford.com/item/3272BR.aspx

Your feeler gauge almost certainly goes past .025. You just need to put several leaves together, like .025 & .010 = .035". Or maybe your feeler gauge is not what I'm picturing.

If somebody else has brought this up I missed it. When installing magnets on the flywheel you may find some of them "stick up too high" (closer to the mag ring). Some folks advocate evening them by pounding the high ones down with a hammer until they are all the same height. I find the idea of whacking fresh magnets with a hammer cringe-worthy. I would much rather avoid that by raising the low magnets enough to be even with the high ones. If I can get all of them within .003" I call it good.

I prefer making shims to raise the low magnets. I happen to have shim stock of .003" and .005" that can be combined if necessary. I don't recall ever having to use more than two shims to get all the magnets to a uniform height (within .003").

You can see shims under the spacers to get all the magnets at a uniform height.


Checking magnets for uniform height.


One ace Model T guy told me once that he set the magneto gap at .010" and it made that car a charging son of a gun. I don't have the guts to do that. The recommended .025" to .040" is close enough for me. I aim for .028" to .030".

I can agree with Steve re pounding on the magnets to adjust the height of the retainers, but with a different reason. I will always use a set of new, machined alloy spacers. The originals are cast, some are cracked when you take them off, and more will likely crack if they are pounded on.

Using a nylon faced hammer to make a height adjustment on a new alloy spacer is OK by me, but only if .002 - .003" is required. The last one I did needed shims to bring two keepers up to the height of the rest.

Allan from down under.

I start assembly by measuring magnets, keepers & spools. Shuffle accordingly & add brass shims to the spools like Mr Jelf does.
The few that may be a few thousands off, (higher) get squeezed down to size in a press. No hammering.

My magnets all seem to be pretty uniform for the most part, I'm not too worried about having a perfectly functional mag, I drove the car without it working for several years and the generator seemed to have no problem keeping up the battery, even with the starter and headlights. I never had to charge the battery.

Off topic, but I think my car for whatever reason has some of the best functional stock 6v headlights and starter I've seen on a T so far. I used to drive quite a lot at night and always felt visibly comfortable, and my starter almost sounded like 12v

This is odd because I went through and cleaned up all the ground spots for the headlights/frame and they were very rusty. It's interesting how different these cars behave despite being mass produced

Anyway, is there supposed to be some reason you're supposed to use mag instead of just battery on a car as late as 24? It seems odd to me that Ford, while trying to save as much cost as possible would still include all of this machining and materials to keep the magneto despite the car being able to run just fine on the battery and generator. Was the generator system really that unreliable?

The engine runs much better on mag than battery. This due to the design on the ignition system.

...is there supposed to be some reason you're supposed to use mag instead of just battery on a car as late as 24?

They're all different, of course, but usually a T of any age will run better on MAG than on BAT if the magneto is working the way it should. From 1908 until the end, in 1927, the ignition switch always had both positions. If the driver wasn't able to pull the crank energetically enough to generate sufficient current for starting, BAT would eliminate any need to pull the crank quickly. It would provide enough juice to fire the coils. But even on later (starter) cars the magneto simply supplied more current than the battery once the car was running. In Model T days batteries were commonly six volts, and that's what most cars used until the fifties.

Some folks think you have to "spin" the engine to start it. No. On BAT there's no need for that.

https://www.youtube.com/watch?v=3pv6HWWOGYA

Carson, it wasn't that the battery/generator system was unreliable but cost in giving the customer the option of the cheapest T, batteries were not cheap for some reason back then, example in 1922 a battery in Fords parts books cost $25.oo and a magneto assembly only $6.oo so a battery, starter and generator added a huge price increase on the base price of the T.

Mr. Man;

Many of the early advertisement talk about how 'THERE IS NO BATTERY EVER NEEDED FOR THE FORD MODEL T!" , so part of it is Henry being frugal, and the other part is probably Henry being stubborn. There was NO change to any Model T that was not approved by Henry Ford, so I think that is really your answer. Henry wanted it, and that's the way it WAS.