Relative magnet height question.

[Darren J]

I reinstalled my magnets and I am using the KR Wilson jig. Reading over the comments on this forum regarding this issue I see people say they shoot for an overall variance of +/- 20 thousands. I can't find any mention regarding the magnet height relative to the trans shaft. The book says anywhere between 13/16 and 53/64. Is this measurement not that important as long as the full magnet set is within +/- 20 thousands??

If I have a high magnet clamp plate because they are not perfectly flat can I just sand down the high spot a bit with a sharpening stone for example?

Thanks, Darren

[Scott_Conger]

It sounds as though you have neither the Model T Service Manual nor the MTFCA Transmission book. You really need both, and spend a good long time reading the appropriate sections.

To speed things along, I'll tell you that the magnet keepers all need to be within .004-.005 total maximum variance between all of them - lowest to highest...I shoot for .002-.003...I don't do this work for others so am satisfied to spend the time on my own stuff and frankly don't ever plan to do another one, either.

After that, when installed on the crankshaft, the clearance between the magnets (keepers) and the coils should be .025-.040, with the higher clearance at the bottom where the coil is unsupported and prone to vibration. Check every keeper relative to every magnet...rotate one magnet width and check again, etc. It is a fun job until it isn't and that threshold is about an hour for me and the rest of it is just slogging through a miserable series of repetitions.

And that's just magnet height - somewhere along the line you really should be concerned with balance, as well. Some of that can be dealt with by varying magnet locations - heavy vs. light. Funfunfun.

Whatever or wherever you have read about this, there is a plethora of both good and bad advice available, so be very careful where you source your info

[TMiller6]

I would not take a stone to the steel. Instead I would adjust the height with the aluminum spool.

A old guy I knew used to hit the steel plates with a rawhide hammer to seat the magnets. T would not use his method as the magnets have been known to crack.

[Mike Silbert]

Darren,

#1 be very careful when working around the magnets.
They love to pick up things from the bench and nearby areas.
This includes filings from the magnet plates.
If you have a burr or ding then it is safest to remove the plate and take care of it elsewhere and return it back.
There have been instances of junk being picked up during assembly leading to problems later.

Everyone has their own opinion about setting these and the service manual says hit it with a hammer.
I prefer to use more care and remove the screw and slip the spool out then dress it down a bit.
But I only will do this on ones that are the tallest.
You can also swap them around since they will not be the same height in a set.
On the rest of the magnets I make shims from a soda can (aluminum) and shim between the spool and flywheel to bring them up in line.
Yes, this is time consuming and tedious but I do not like other methods.
I usually set them to better than +- 0.010" myself, but that is me

Why? My reasons...
When dismantling stuck (overtight) screws that are flat heads hit them with a hammer and you will be amazed how much it stretches the fastener and loosens it up.
Impacts can reduce a magnets strength
I have seen the screw heads broken off and the plates come loose when driving, remember they are brass.
See this forum post: viewtopic.php?f=2&t=51531
And if you study the way the magnetos are built the bend of the V is sitting on a ledge and it somewhat automatically sets the outer edge magnet height. If you go too far (up or down) it puts everything in a bind so the fasteners will not work as designed.

The overall height of the magnet / flywheel assembly will be adjusted with the shims between the Magneto Ring Coil and the Block so it needs to just be in the range.
The crankshaft position fore and aft (also a variable in the final magneto gap) is set by the thrust surfaces on the 3rd main bearing.
The transmission output shaft will slide in and out of the 4th main and U-Joint so it will compensate for any normal range positioning.

Others will chime in with how they do it.
Mike

[speedytinc]

.005 variance is probably OK as a max. I also shoot for .002"
This is a time consuming job. Take the time.

Heres how to minimize the work by being smart.
Measure all magnet leg thickness - note it.
Measure the spool heights & keeper thicknesses. Mark them.
Shuffle accordingly. Add .010 brass shims to the spool bases if necessary.
That will get you with in .005.
Install the magnet bolts, but do not tighten.
Install the brass screws.
Start checking the keeper heights with that neat krw tool. Hopefully you read the instructions on it.
High keepers can be squeezed down. Big C-clamp or press. Watch you dont shatter a spool.
Tighten the brass screws as you go. When you get all the keepers the same height, then torque the magnet bolts.
Every screw & bolt tight, upset the ends of the brass screws.
Check F/W balance & remove iron as needed. I use a big drill bit with a shop vac nozzle close to suck up the filings on the magnet side.

[Mopar_man]

I'll say this: Once you get your magnet hight set take your time with the gap between the Mag ring and the magnets. Getting this gap correct will give you more power, make the T run better, and some say solve world peace. I had my fly wheel on and off the engine many times as I sliced shims to get it right.

[Darren J]

I do them them both Scott I referenced the specs in my original question

[TFan]

One thing I would add to the mix is have the engine nose down when setting your mag to magnets clearance, that keeps the crank all the way forward and takes out any play so you don't get it set too close when running. Good luck and keep your patience". Jim

[Darren J]

Thanks. Yeah it’s not a patience thing really. I’m retired so time is not an issue just wondering what you guys do as far as height from trans face based on the service manual. Since we have some play with shims in the field coil as well seems to me just finding the midway point should be fine. What I don’t see here is common ground regarding overall variance on the plates. I see many people talk about 20 and I’m already there so do I really need to work on it some more or am I good?

Thanks, Darren

[Scott_Conger]

so, again,

the magnet keepers all need to be within .004-.005 total maximum variance between all of them - lowest to highest...I shoot for .002-.003

It would be pretty tough to set a gap of .025-.040" to the coils if the magnets varied up to .020 between each other.

perhaps I am missing something in translation?

[Darren J]

That’s what I was looking for Scott! Thanks I’ll shoot for that in the morning.

Thanks Darren

[Ron Patterson]

Darren
Many people do not know it, but the K.R. Wilson Magneto gap gauge serves TWO functions.
One, to assist with correctly setting the magnet height when the flywheel is fully assembled l and two, to facilitate setting the magnet to field ring poles gap. Notice the tip of the tool head is made of non magnetic stainless steel to help with this task. Most people are familiar with this use of this tool.
But study the following diagram below carefully.

After setting the magnet height you can also rotate the head of the tool head 180 degrees and by placing a transmission flange into the flywheel you can use the tool head to set the field ring circular magnet to field pole gap.
But, here is where things get a bit sticky and you need to remember John Regan's favorite saying about Model T's; "the car is a hundred years old, a hundred people have been working on it and what are the chances they all knew what they were doing?".
Using the KRW gap gauge assumes the rear crankshaft bearing cap thrust surface (both sides) were finished as Ford intended (NOS or using the KRW method) and the field ring to engine block mounitng and field pole surfaces have no been changed when previously setting the magneto gap.
To say this another way; when setting the field ring to magnet gap it is imprtant to remember the rear main cap and field ring may have been modified or is otherwise not set the way Ford intended. This affects the seecond use of the gap gauge. Many used fieldrings have been modified by grinding away the poles or the mounting flange when setting the magnet to field pole gap.
Think about it and you will understand.
Hope this helps.
Ron Patterson

[TXGOAT2]

If the magnet heights are not at spec and equal, the output voltage/current profile will not be the same within each revolution of the crankshaft. If one or more magnet retainers is high, the rest will have to be too low, increasing the average gap and reducing the output of the balance of the magneto.

[Scott_Conger]

Darren

there is another bit of a pitfall that you need to be aware of...perhaps you already are or perhaps this will be news, but in any event, here goes -

you MUST NOT reuse your brass screws - brass crystalizes and is prone to breaking if under stress and has been aged and thermo-cycled (they'll be too short to peen over, too).

you MUST match the new screw threads to your ring gear - if the ring gear is original to the car, you must use screws that match those threads (#14 x 24) - if the ring gear is new, you must use screws that match those threads (1/4-24). If the screws feel slack and are wobbly as they screw in, they are WRONG.

[Ron Patterson]

Pat
The field windings are wound in series, therefore the output of the magneto at any given time is the sum af all the field windings current.
The output does not vary per rotation.
Ron Patterson

[Ron Patterson]

I should have worded the last sentence of my post immediately above to read; Assuming no change in RPM, the magneto output does not vary per rotation.
Ron Patterson

[speedytinc]

When everything is in spec, & the KRW tool used properly, the F/W gets bolted in place & the field coil clearances are correctly set.
One install & no removal & replace multiple times. Oh, if it were only so. Chances are slim that all the stars align.
However, Using the tool to set the field coil will get you closer faster. The coil will be, at least, square & with proper clearance spread top & bottom, & side to side. Installing the F/W will show actual clearance. At this point either, adding or subtracting shims evenly will get you in spec with only the need to remove the F/W once. That's a time & back saver.
Without that initial setting, the process usually requires a minimum of 6-8 R&R's & many shim adjustments. That's aggravating & time consuming work.
But, so worth it when you can start your T on mag, cold, with one 1/4 pull.

[TXGOAT2]

The effective strength of each magnet will vary if the gap varies.

[Art M]

The best advice I can offer is to follow what Scott Conger said and to take your time doing it. I have only done one in my life and the results were very good. It took me several weeks to get what satisfied me. I hope to never do another one, but I am always willing to charge the magnets for other people after the magnets have been arranged. I like to magnetize each one individually. Good Luck.

Art Mirtes

[Henry K. Lee]

I second the motion on Scott's suggestion! I have had a half of the head break off after a year or so..., got very lucky!

[Darren J]

You guys are awesome! Thanks for all the responses. I'm new and learning as I go. I was able to get all my magnets to within 3 thousands of each other. Dang that was an effort. My new field coil is super close finally. After about 3 hours and trying different shims for maybe 30 different attempts. I am going to finish up in the morning. I'm a little tighter than 25K at the moment so I need to address that but thanks to all you guys I'm pretty close.

Thanks a lot guys, Darren

[Dan Hatch]

Have a question. What is under the spool circled in yellow?

[RajoRacer]

Appears as though he shimmed up a few - I see a couple.

[Mike Silbert]

Just a comment and my preference:
I would drop off the generator and carburetor to make getting all the pan bolts & cotter pins installed.
The manifolds can stay if you don't want to mess with all the gland rings or remove them if desired.
Or make it like a '27 style and use lock washers to save some aggravation.

He spent a lot of time making the magneto great so dare I ask how true the transmission shaft is running?
It looks good, keep up the good work

Mike

[jiminbartow]

If you position the transmission horizontally to adjust the magnets, keep in mind that when the transmission is installed in the car vertically, the weight of the transmission will cause the upper measurement to open and the lower measurement to close which needs to be compensated for. Ideally, the measurement should be uniform on the top and bottom when the transmission is vertical. Very tricky. When I did mine, I must have assembled my transmission two dozen times until I got it right. That was a long, exhausting night.

[Henry K. Lee]

As Jim as said about the differences I have set up the engine at a 30 degree angle to compensate the sag so to say. Never had an issue and was very happy with the results. My Dad at 94 taught me this trick some years back, he has been playing with T’s since 1944. Just a little field experience he calls it.

Awesome job Darren!

[Darren J]

Those are aluminum shims under the spools. That was easier on some of them.

When I removed the inspection cover to check my clearances I noticed the crankcase bolts all had lock washers and thought I’d try to make it more original whether it came this way or not from the factory so a went to the trouble of buying new bolts and drilled them all out for cotter keys…etc. I mistakenly forgot about the pans and needed to remove the cotter keys and yada yada. All this while the motor was still in the car. End result…lock washers from here on out. What a pain

[TXGOAT2]

How much end play in your crankshaft?