Magnet Retainer Plate Level on Flywheel

[MadMax]

I've been reading the tons of posts on the forum about setting the brass screws for the magnet retainer plates. Folks discuss having the plates all in the same general plane and within a certain tolerance of each other in that plane. I've seen where folks say not to tap down the plates to adjust heights because of killing the magnetism of the magnets.

With mine, I have all new retaining plates, screws, and spools. The magnets were recharged.

I made a rig to see whether the plates are at about the same height

But when I ran the dial indicator over the pieces, I was surprised that there was a 'slope' across the plates.

RenderedImage.JPEG (48.8 KiB) Viewed 5932 times

I'm guessing this is due to the magnet thicknesses. This can be quite the difference in height too. I decided to take some time and went around the set of plates and measured the height from the back side of the ring gear to the top of the plates (on both sides) and found that these have a big difference in some places (or what I feel is a big difference)

Is this something I should be worried about and if so, how do I fix it? I tried sanding/grinding off one side of a plate for S&G. Is that a bad thing to do?

[Adam]

The new plates aren’t really made right. You are better off using good used ones.

[Scott_Conger]

because it's set by clearance, you obviously have to set to the highest or closest gap on each one when shimming the spools (at least I shim the spools, and others do, too. Others just smack the things to set the height of the magnet through compression of the spool and maybe level the keeper in the process). It is the most annoying job there is on a "T", in my opinion.

you are also going to find some variability across the magneto ring pole faces...funfunfun!

If you're using new keepers, think about this: I've found that new keepers are very soft and prone to warping...old ones are cheap and far superior

you're finding out why some folks go to extra lengths to match magnet thickness, etc.

good luck, and remember the hobby is FUN! (Keep repeating this)

[speedytinc]

I measure the thickness on the spools, magnets & keepers & try to mate for even height. Real shorts I might add a .010" shim washer.
Heights still need tweeking.
To adjust (lower) the height I use a big C clamp with a thick hardened washer as a spacer to protect the screw on the back side. I have broken a few aluminum thimbles. Goes with the territory I guess.
Yes, its a pain & time consuming job. I dont mind for my own motors. Yea fun.

[ABoer]

Max ,I turn down the Support Spools if they are to high .
And always use old plates .

Toon

[Steve Jelf]

The gap between the plates and the field coil is supposed to be .025" - .040". I guess if everything is within that .015" spread it's good enough. But I prefer to match magnets for thickness and raise the low spots with shims under the spools to get as much of each plate as possible near .025".

[MadMax]

Hey Steve, I saw where you posted the shims a couple of weeks ago. It prompted me to buy some brass shim stock so that’s where I got the idea to make them. Many thanks!

[MadMax]

By the way, are those brass spools???

[browning]

For what its worth, I have been experimenting with rare earth magnet replacements for the Model T flywheel just for the fun of it and in order to test the output of the experiment I mounted a "T" flywheel to the chuck of one of my engine lathes and mounted a newly rewound magneto to the carriage so that I could predictably adjust both the speed of the flywheel and the distance between the pole pieces and the magneto face. This has been illuminating and interesting. I can change between the rare earth flywheel and a newly recharged stock Ford flywheel in just a few seconds making comparisons easy. The stock flywheels I have used were recently recharged so that the magnets would lift my test weight of 4 1/4 pounds and output voltages were checked with an antique analog ac voltmeter, a new digital ac voltmeter, and an oscilloscope. The readings were slightly different but pretty darned close, repeatable, and stable. One of the questions that I have always had was what the relationship was between air gap and voltage output. That can't be easily checked in an engine installation but very simple with my test setup since all I have to do is increment the carriage away from the flywheel and check the voltage. You may find the following findings helpful in setting your flywheel clearances.

I ran the lathe at 1550 rpm for the following test. With the air gap set at .010 (way too close for an engine) the voltage was 16.6 vac. At .020 it was 15.4 vac. At .030 it was 14.4 vac. At .040 it was 13.8 vac. At .050 it was 12.9 vac. At .060 it was 12.4 vac. At .070 it was 11.9 vac. At .080 it was 11.4 vac. At ,090 it was 10.9 vac. At .100 it was 10.5 vac. I was surprised that as the gap enlarged the degradation diminished, who knows why? Maybe this will assist you in your adjustment.

[MadMax]

Hey David, I was speaking to a friend in our club about rare earth magnets. I would’ve expected them to do even more!

It’s great that you are doing a test like that.

Obviously, there is never any disagreement among the people in the forums about how things work, and how to fix things.

This testing gives everyone concrete information on what is really going on! Many thanks!

[browning]

Max, The rare earth magnets did outperform the stock ones exponentially. The air gap could be increased to over 1/2" and still perform well. The problem would undoubtedly be how to detune the rare earth flywheel to where it was hotter than stock but not overwhelm the ignition coils. I'm still working on that. I started with the largest samarium cobalt magnets I could fit into the aluminum holders but will probably wind up downsizing them once I figure out what it is that I'm looking for. One of the other tests I intend to do is to introduce voltage to the magneto while the flywheel is turning to see how much more stable the magnetism is in the rare earth flywheel than the stock one.

[Steve Jelf]

...are those brass spools???

Yes. I don't see anything in the encyclopedia about when they changed to aluminum, but they were brass at least until the mid-teens.

[Scott_Conger]

There really is no mystery why the rate of change drops off...and no mystery as to why force vs distance is not a straight line

Coulomb's Law: force is inversely proportional to the distance squared...Ron Patterson has referred to this on multiple occasions, but he doesn't seem to frequent the Forum much these days.

Examples:
If the distance between two magnets is doubled the magnetic force between them will fall to a quarter of the initial value. (F/4)
If the distance between two magnets is halved the magnetic force between them will increase to four times the initial value. (4F)
If the distance between two magnets is increased by five times the magnetic force between them will fall to one twenty fifth of the initial value. (F/25)

as mentioned above, because it changes at a rate squared, the drop off is not a straight line

You can use Coulomb's Law to derive Gauss's law if you want...but who'd want to, to just work on a "T"?

Not my area of expertise, but did spend a short time designing and fabricating custom Hall Effects switches, so had to dabble in that realm. Didn't really enjoy it that much.

[MadMax]

That’s wild about the brass spools!

Polish them much???

[Art M]

I spent a lot of time matching the magnets, spools and plates. In the end, the plates are within about .002 inches of each other. I set the minimum air gap at .020 in. After 8000 miles the engine starts very easily on mag by hand cranking.

Some people randomly assemble the pieces, then true the surfaces in a lathe.

Art Mirtes

[Allan]

If you want perfection, do all the shimming, tapping, pole swapping and magnet matching to get things as close as you can, then have the flywheel machined as you would when surfacing the clutch face on a conventional flywheel. That will clean up any discrepancies in height as well as any tilt in the keepers. There is no need to go any further than finding a grinding register on all 16 keepers. You do not need to get a full surface grind on every keeper.

Allan from down under.

[speedytinc]

If you want perfection, do all the shimming, tapping, pole swapping and magnet matching to get things as close as you can, then have the flywheel machined as you would when surfacing the clutch face on a conventional flywheel. That will clean up any discrepancies in height as well as any tilt in the keepers. There is no need to go any further than finding a grinding register on all 16 keepers. You do not need to get a full surface grind on every keeper.

Allan from down under.

Wouldnt that make for metal fuzz everywhere on the magnet surfaces? Tough to clean up off fully charged magnets.

Its not that difficult to get .005 max variation with a krw type tool.
The thing I use is a rod on a D/S inner sleeve on a trans center shaft. In the wrist pin is an adjustable bolt that floats over the keepers. With a little downward pressure I go around & adjust until contact feels the same on all keepers. I think I get no more than .002 variation when done.
Good enough.

[MadMax]

I would think that if you machine the whole face, you would have to disassemble everything, clean, everything to make sure that all of the grindings and shavings are gone, then reassemble it.

Because of the variety of magnet thicknesses, I would think he would have to map all of the parts to make sure you put them back in the same place.

For those of you that have done that, is that the way you handled cleaning it or is there another way?

[Steve Jelf]

Because of the variety of magnet thicknesses, I would think he would have to map all of the parts to make sure you put them back in the same place.

I believe machining the face of the whole assembly is overkill. Using shims I get a variation among the plates of less than .005". I call that good enough.

[Allan]

You are right Steve. Overkill it is. But there are those who feel the need to build a T to far greater accuracy than is ever needed. My godson came up with the grinding idea, because they could, when I left my flywheel with them for balancing.

Allan from down under.

[MadMax]

Many thanks for the word, all!!!

[J and M Machine]

[quote="Steve Jelf"
I believe machining the face of the whole assembly is overkill. Using shims I get a variation among the plates of less than .005". I call that good enough.



For the people that want the best for their Model T, it's not overkill.
We resurface both flywheel and the mag field so that the T gets all the power to the wheels it can.
Free starts aren't uncommon.

[speedytinc]

So, you do machine/surface the magnet keepers? How do you remove all the metal shavings?

[Allan]

I Don't know how the machine shop de-fuzzed my flywheel. I used high pressure air to blow down the flywheel before fitting it, as a matter of course. Any fuzz accumulates on the pole ends of the magnets, and you can pinch it off with your fingers if you wish. I find more fuzz on the magnet in the trans cover screen after a rebuild than I ever found still sucked onto the flywheel after grinding.
Your results may vary.

Allan from down under.

[MadMax]

Okay, here’s an update. After not trusting my tool, I went through the process of measuring the total height from the back of the ring gear to the top of the retainer plate.

I’m pretty happy with where they are height wise, but managed to buy a KR Wilson tool on eBay. So I want to do the check with that.

Small problem though. When I try to put the KR Wilson tool in the opening of the fly wheel, it drops down on the pins in the fly wheel, but gets stuck about halfway down. I’m not sure whether I should expect an interference fit or whether you would normally take those pins out and then bolt it down.

Any thoughts?

[RajoRacer]

You need to space out the base of the KRW tool - I cut the shaft off a T transmission shaft & use the flange as a spacer - works perfect.

[Scott_Conger]

Max

Steve is correct. Now you need to ask "why is that?". And then start doing some research on the forum for how to ACTUALLY use the KRW tool...it does more than just check keeper level(s), and to just tell you WHAT it does without a full explanation of HOW it does it would be a disservice to you. It's a pretty ingenious gizmo.

[MadMax]

Many thanks guys!

I’ve been reading the forums about the use for not just the magnet side, but the field coil side. I didn’t realize it was able to help calculate the space between the field coil and the magnets [that but figured it had another purpose since it could rotate].

I have at least one water transmission shaft that I can play with.

[Dan Hatch]

KRW mag gage?? Seems to me I saw a Service Bulletin on that thing somewhere. Where did I put that thing?

[Sean Butler]

I think I've got your back, Dan. While the Service Bulletin never instructs to use a tranny shaft as a spacer it does allude to it as seen in the highlighted text on the second page. Also, be sure to verify the trueness of the bottom of the flange on the KRW gauge. I have a repop gauge and the flange was off just a hair and needed a cleanup cut to get it true. Click on the photos and they should show larger.

[Dan Hatch]

Read paragraph 2 of Service Bulletin.

“ Make sure transmission shaft is clean and free of nicks.”

They are expecting you to be doing this on complete transmission.

Also floating around somewhere are the instructions for setting the mag gage. Where did I put those?
Good thing my shop is just one room!!!

[Sean Butler]

Good catch, Dan. The following link has Ron Patterson's info on calibrating the gauge:

http://www.mtfca.com/discus/messages/11 ... 1269355108

[speedytinc]

Read paragraph 2 of Service Bulletin.

“ Make sure transmission shaft is clean and free of nicks.”

They are expecting you to be doing this on complete transmission.

Also floating around somewhere are the instructions for setting the mag gage. Where did I put those?
Good thing my shop is just one room!!!

You dont have to have a complete transmission, but you do have to have a center shaft installed.

[Art M]

Speedy,
The trans shaft flange goes between the crankshaft flange and the flywheel. It is needed. I only put one engine transmission together and that is what I remember.

Art Mirtes

I

[speedytinc]

Speedy,
The trans shaft flange goes between the crankshaft flange and the flywheel. It is needed. I only put one engine transmission together and that is what I remember.

Art Mirtes

I

Thats basically what I said. The trans shaft has to be in place, but the rest of the transmission need not be.

[Sean Butler]

Quick demo with the closest (and dirtiest) "props" at hand.

[Allan]

I parted the flange off a worn shaft so that I do not have to work around that obstruction. It makes it easier to work on the flywheel on a bench.

Allan from down under.

[RajoRacer]

That's what I posted a few days ago !