While driving my 1926 T roadster pickup, I heard a clunk followed by very rough running. I switched to battery and got home successfully. I think one of the magnets came off of the ring gear.
What must I do to diagnose and repair the problem?
Must the engine and transmission be separated?
That does not sound good. You can likely remove the starter and peek in and confirm the problem. Then if you lost a magnet the engine/transmission will have to be separated for the repair.
Just a reminder - when you remove the starter, remove the bendix FIRST, then you can remove the starter motor. If you don't remove the Bendix first, you will likely damage the covering on the magneto ring, and then it will have to be replaced also.
While driving my T a few years ago I heard a clunk which was followed by very rough running. The crankshaft had broken. I do hope that you have something less grave.
Good luck with your project. Bill
Yikes! Definitely sounds like you need to peek through the starter hole. You can also see a lot of stuff if you pull the oil inspection pan. The more you know before you pull the engine the better.
I had essentially the same thing happen - I had recently gotten the T from my grandfather and started driving it a lot. An old key that got dropped in there worked itself free while I was going down the road - heard some clunking and then started running rough then only would run on battery. It had chewed through magneto wire.
I don't think that you have entirely thrown a magnet. If you had, you would not have been able to make it home on BAT. I think your mag-ring (coils) may be damaged.
This same thing happened to me in my 27 tudor. The only way to repair the problem was to take the engine out. I had done this exercise many times over the decades, but i'm not as spry as I was 40 years ago, so I built some fixtures using left-over lumber scraps, making it easy to dis-mount the transmission on "the floor." See the attached photos:
I took the opportunity to replace the mag-ring with a newly rebuilt unit, charge the magnets, tune up the coil/magnet separation, replace the starter ring-gear, and take care of the nagging oil leaks.
The T runs fine on BAT, but it runs so much finer on MAG!
If you need any help just let me know. I am near St Cloud.
Ken, That doesn't sound good. I'm sure there are about a hundred other guys on this forum who'd know better than me, but if I were you I'd pull the transmission inspection cover, starter, and oil pan inspection cover and start looking around before pulling the engine out of the car.
James, that's an interesting magnet charger you built there. Any special instructions on magnet charging?
Recently a friend of mine lost his brakes but drove home using the reverse for a brake. He said as he was on the way home he heard a noise like marbles in a blender and the magneto stopped working. He was able to continue on battery.
I thought he had collapsed the reverse drum which hit the magneto, but when we pulled everything down, the drums were fine. The lining was gone on the brake band. Upon further inspection we found the babbit was gone from number 4 rod. The babbit had gotten caught between the magnets and the coils which cut the coil causing the magneto to quit. The noise he heard was the rod knock.
We then turned the crankshaft and poured all new bearings, replaced the magneto ring and the band linings. We recharged the magnets and put everything together. (we did some other work not related to this problem).
His car now runs better than ever.
So the problem could be something other than your first suspicion. Usually if a magnet breaks off, it will punch a hole in the hogs head and the engine will stop so fast your wheels will skid. So maybe something else caused your problem. At any rate, you should quit driving until you find and fix whatever is wrong.
"Usually if a magnet breaks off, it will PUNCH A HOLE IN THE HOGS HEAD . . ."
Most likely, a magnet keeper let go because the mounting screw has crystallized with age.
By looking through the starter opening you can have someone slowly crank the engine and see if they are all there....bet one is missing. Time to pull the engine either way.
BTW interesting story Norm. I would have thought that losing #4 rod would have made a heck of a racket.
Not in all cases, Seth.
When an undisclosed, errant band washer found it's way into a space not large enough for it & the magnets, half of them "came from together" and bunched up in the bottom of the pan resulting in a very sudden stop of the engine ! This was in my wife's '25 Coupe a week after we brought it back from Montana. It supposedly had been "parked" for 20 + years and one could assume that was the reason for parking it and walking away !
My comment should have been directed to Norm - not Seth - apparently Seth had re-itterated what Norm had posted.
I was just quoting what Norman stated and then posting the "scared" face. The idea of a magnet coming loose and punching a hole through the hogshead makes my skin crawl.
The magnet charger is just two lathe-wound magnets connected together with an iron bar, bent so as to give direct contact on the magnets. It's a variation of the unit described in the club publication on Model T electrical systems.
The power supply is a high-current, 28-volt, army-surplus unit, modified to give a half-wave rectified output. The resulting DC waveform gives a 50 percent duty-cycle, and it "bumps" the magnets at 60 Hz. This gives an effect similar to heating the magnets with a torch or beating on them with a ball peen hammer. It slightly enhances molecular motion, which encourages molecules to align on a common magnetic axis.
Seems to me it's unlikely one of the magnets became entirely detached. In that case, the unbalanced flywheel would be vibrating badly enough that you'd feel the need to panic-stop the engine rather than limp home on battery power.