Why does the engine die when i switch it to magneto!

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Model T Ford Forum: Forum 2013: Why does the engine die when i switch it to magneto!
Top of pagePrevious messageNext messageBottom of page Link to this message  By mike taylor on Thursday, January 03, 2013 - 09:58 pm:

my t will die when i switch over to the magneto. 22 electric touring. new battery, plugs, commuter rebuilt and timed. any help will save me money! semper fi and happy holidays!


Top of pagePrevious messageNext messageBottom of page Link to this message  By joe bell on Thursday, January 03, 2013 - 10:11 pm:

Warm the car up on battery then hot wire your coil box directly to the mag post, if it fires then your problem is else where, if not you have magneto problems. I have found that many a times people have a bad switch. This is just a quick dianostic check.


Top of pagePrevious messageNext messageBottom of page Link to this message  By joe bell on Thursday, January 03, 2013 - 10:12 pm:

Make sure you remove the battery wire from the coil box, sorry!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Thursday, January 03, 2013 - 10:16 pm:

Your flywheel magneto has no output or there is a wiring error, or switch problem.

Remove the floorboards and the wire to the magneto terminal. Start the engine and rev it up to a fast idle. With an analog voltmeter, not a digital meter, measure the output voltage. You should have about 12 volts ac. If you don't have a meter simply short the terminal to ground and see if you get any sparks. If no sparks or volts,kill the engine and remove the magneto terminal and see if it is shorted to ground. If its OK then it may not be contacting the magneto coil. The needle point on the terminal contacts a solder pad on the mag coil and the point may have worn a divot in the solder pad. You can run the engine with the terminal removed and measure the voltage directly from the mag coil solder pad. You will have some oil thrown up through the hole so have a rag handy.

The more detailed method attached should be used if you have output from the magneto.

application/pdfMagneto Test
MAGNETO_TEST.58163152.pdf (95.3 k)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dan Treace, North FL on Thursday, January 03, 2013 - 10:20 pm:

If it worked before, the MAG position on the switch may have worn contacts now.

Or the mag post may have debris that is grounding out the mag when you switch it from BAT.

Easy to remove the mag post and clean it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Richard Wolf on Thursday, January 03, 2013 - 10:20 pm:

Mike;
Welcome to the forum. There is a lot of guys around you that have Model Ts.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison_Rice Minnesota on Thursday, January 03, 2013 - 11:53 pm:

Check for debris on the contact end of the magpost. Then put things back together and check the voltage as described at the magneto contact.
No Voltage means you've got to measure the crankshaft endplay. If you've got juice work your way up to the switch. If the switch is good then go to the coil box, then the timer. All of the continuity checks can be done with a digital multimeter but you'll have to use an analog voltage meter to check the magpost. That darn magneto creates Alternating current because the magnets are going past the coils in there first the positive ends and then the negatives. There for the juice is switching from + to - and back to + and then to - and on and on. It'll probably make a pretty nice sine wave on an oscilloscope. And there's so much transient power leaking around that darn thing a digital voltmeter just can't keep up.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Bishop, San Diego on Friday, January 04, 2013 - 02:40 am:

Mike,
I had the same problem, but had done an in-car magnet recharge before (after the previous owner installed the new battery backwards and demagnetized the magnets. Thought I'd try it again, and it worked until I switched from "battery" to "mag". Wrote the forum. . .received all the same answers. Some good, some over the top (like removing the engine and fixing crank end play).
Try the simple things first, like continuity checks suggested above. You can follow the wires all the way thru the system. You can also switch the bottom two wires on the engine side of the firewall between the battery connection and the mag connection to check the switch.
Mine turned out to be a short in the switch, very easy to fix, but told by many knowledgeable people on here that it never happens and I would have to take the engine apart.
My 2 cents. . . .take it easy, step by step, easy fixes first (lint under the mag post, continuity segment by segment, etc). Even try an in-car recharge of the magnets (e-mail me for directions). It might not help, but won't hurt anything and doesn't take long--maybe 20 minutes. Rule the simple things out first before getting too ambitious.
Try to find someone in your area who can help. Makes a big difference. Good luck


Top of pagePrevious messageNext messageBottom of page Link to this message  By mike taylor on Friday, January 04, 2013 - 07:16 am:

thank you all! i am new to model t's (my pop had them when i was little). have a barn find and am quickly finding out how much fun the cars and the community is. again, thank very much!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Friday, January 04, 2013 - 03:39 pm:

Installing the battery backward would have no affect on the magneto, but if the battery were to be connected directly to the magneto, it would discharge the magnets. Do not do what Joe Bell said to do unless you first disconnect the battery from the coil box. That can be done by turning off the ignition, but better yet disconnect the wire at the coil box. You will need to start with the starter with the wire connected to the coil box.

Most likely what Bob Bishop did was to get the wiring mixed up so that the battery was connected to the magneto instead of to the coils.

Mike, has the T run on magneto before and just recently stopped running on magneto? In that case, the first thing to check would be the plug at the top of the magneto to be sure there is no band material or other debris at that contact. When that is cleaned try to run on magneto again. If it still doesn't run on magneto, check with an analog AC volt meter to see if it has at least 6 volts AC at low speeds and reaches about 25 volts at high speeds. You can make this test while running on battery. If the output of the magneto tests good, then check all connections between the magneto and the coil box. This would also include the ignition switch.

If it did not run on mag when you bought the car, then it could be anything from no magneto in the car to endplay in the crankshaft to discharged magnets or to open connections between the coils on the magneto ring.

If it stopped after you bought the car, it could still be discharged magnets, crankshaft endplay, or open connections on the magneto rings

Good luck on finding and correcting the problem.
Norm


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