I was driving home the other day and I heard a sound that sounded like my fan going through my radiator. I turned it off and got out and thankfully, no radiator damage but my fan belt was coming apart. I cut it with a knife and drove a 1/2 mile home. I did notice it wouldn't start on mag so I figured it was flooded and switched to battery and it was fine. I switched to mag and it ran fine.
I replaced the fan belt and I've ran it several times at idle. Today I went for a short drive and then home. I cranked it in the garage and then suddenly there was the same noise. I'm out front so I pull the choke to kill it real quick. I look and the fan is fine but the noise sounded like it was coming from the rear. It wouldn't start again so I switched to battery and started it. No noise but when I switch to mag it dies. I've started it several times and it runs fine on battery but dies on mag. It hasn't made the noise again but something I'm afraid is loose inside.
I've got a spare motor and I don't want to drive this one with something loose inside. I was wondering if anybody has had something similar happen? Maybe a mag clamp screw loosened up? But if a clamp were hitting then I don't know why it would be intermittent. I sure wasn't planning on a complete teardown but I bet it's not something simple.
You're going to eventually find that the fan belt was a red herring.
It sounds like you slung off a keeper and the next time you heard it, it was busy working to severe the field coil circuit. The next thing is to break a magnet and you don't want to go there...though you may already have one or more broken as it is and they are still where they belong. Time to quit while you're behind.
Pull the hog's head and assess things. There is no good news associated with that sound.
That's what I figured. When I got the motor one of those screws was loose and a magnet clamp was rubbing the field coil. I was thinking thinking something similar happened. Maybe I should freshen up the whole motor because I've learned a lot since I was 15 when I put that motor together. 40 now. My other motor I'm sure is better, just the wrong year but it's going in a speedster.
From what you've just said, I think you've done quite well with that engine. If it was running well, you might be able to freshen it up pretty quickly.
I am in the exact same boat as you with one of my cars...bought it as a basket-case. Got it running quite nicely, but no mag. Moved to WY and 2500 miles of bouncing on the trailer, what did I have when I got here? Well, I got an engine that sounded like gravel was dumped into it...In fact never again started it. Decided to freshen it up and found as expected, the transmission had pretty well blown up. All loose pieces were safely wedged away for my drives in FL, but boy did they work loose during the trip out west. Was a miracle it didn't fly to pieces under my feet. Anyway, my refresh got expensive as I couldn't bring myself to JUST do the transmission.
Try to keep control of the spending if the engine was a good runner and you'll be on the road in no time, with little invested.
Best of luck.
It will give me a chance to recharge the magnets anyway. I'm sure I peined the screw I replaced but never touched the others. Maybe one of them loosened also. Pre internet I had no idea about recharging magnets, just setting the gap. I also don't know if the guy that ground the crank put the proper radii on the journals. That bugs me because of reading about broken crankshafts. Maybe I'll just fix the mag. Crank is still going anyway for now.
I had an engine that was purring just fine in a chassis. No bands dragging just running as smooth as can be. Suddenly it abruptly stopped, could not torn it over. Even tried turning it backwards while stepping on rear wheel spokes with it jacked up. A magnet clamp screw had broken and the clamp had lodged between flywheel teeth and just over the starter. ruined the mag coil ring and snapped 9 of the 16 magnets. That has been over 10 years ago and I tore it down and the motor is all crated up in the garage yet. One of these years I will get it going again as I would like to put a speedster together with just a stock motor.
Those brass screws become brittle and the heads pop off. When I redid this transmission, I filled off the peined part and put a screwdriver on the screws (that were still doing something). Five of them had the head come off under the screwdriver with no perceptible force on my part. It was a remarkable example of what heat, stress and time can do to metal, particularly brass.
Regarding transmission rebuilds, other than magniflux or similar test on the drums, often times, less is more. Triple gear bushings from Bob's is a smart thing. Do some forum searches to see why Bob's is a good choice...it is. Fit them with generous clearance. It is unlikely that the drums need new bushings...they can often go forever.
And whatever you do...replace all brass screws and aluminum standoffs. It is cheap insurance.
I did all that on my 21 motor. Individually charged the magnets with new screws and spools, rebuilt mag ring and it works great. To me that mag and coils ignition system is what sets the car apart so I'll fix it top notch this time.
I think something has come loose inside the transmission and got caught on the flywheel. This has damaged the magneto. I had two such things happen to me on the same car with different engines at different times. The first thing that happened was one of the bolts on the back of the brake drum which bolts to the output shaft came out and went around the flywheel then landed on top of the oil filter screen under the inspection plate. That took out the starter ring on the flywheel. The mag already did not work so I don't know what it did to the magneto.
The other thing happened shortly after I installed a rebuilt engine and transmission because of the problem noted above. This time the first time I took it out for a drive, I was running on magneto and all of a sudden the magneto quit working. I switched to battery and it ran fine. I drove for about 10 years on battery. Then when I was restoring another T, I rewound two magneto rings and decided to put one in the car I had been driving for 10 years on battery. I found that the funnel from the inside oil line had broken off and was laying in the crankcase. It had cut the magneto coil as it came off. Fortunately I had a magneto post oil line.
Anything which gets caught on the flywheel or magnets can cause the magneto to quit working, but it is important to find out what it is because if it is one of the keepers held by brass screws, you have the potential to break a magnet. If that happens, you are in for big damage.
Because you heard the noise, I would suspect something is on the magnets. Sometimes you can see it if you remove the starter and inspect the magnets as they pass by the opening as someone cranks over the engine with the crank. Anyway, hope you find it and can repair it.
I took off the inspection plate and mag post this morning and as I had expected didn't see anything. I'll pull the hogshead next I guess. No starter so I can't look through there. I'm just glad I didn't see a bunch of shredded copper. At least if the coil is damaged it didn't make a big mess.
I recently ordered a remote camera from www.buylizardcam.com in case something like this happens to my engine or if I dropped something into the pan. I have not received it yet, but, in reading about your dilemma it seems like this would be the perfect use for this little remote cam. Good luck. I hope it is not as bad as it sounds. Jim Patrick