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Magneto problems
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- 5+ Years
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- Zip Code: 35757
- Tractors Owned: 1949 Cub
1950 Case SC
Magneto problems
Hi everyone, need some help. I wasn't getting any fire out of any of my spark plug wires, so I made sure it was timed right, replaced the cap, did some cleaning on the rotor, cleaned the points, made sure the gap was correct, replaced the spark plugs, and I started getting fire out of 2 of the wires, the number 2 and 3 cap towers, 1 and 4 did nothing, checked the fire coming out of coil, and its the same thing. The points look ok, but I read you can do a resistance test by putting 1 lead of the meter on the kill switch post and the other to ground. It said with the points open I should get a reading of 3k to 8k ohms, I did that and it read 4k, so I figured it was the correct reading. It said with the points closed it should read 0 ohms, problem is I was getting same reading of 4k ohms with them closed. I am not sure if I did the test correctly, but if I did, what could be causing that? I was thinking the coil may be bad, but I didn't want to spend the money on one if it was something else. I would appreciate any information on this. Thanks, Brett
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Re: Magneto problems
It sounds like you're doing the test right. The test indicates that the points aren't really closing at least on the two cylinders that aren't firing. I'm guessing that something is bent or worn (shaft bushing maybe) causing the point gap to vary through one revolution not allowing the points to close at all four positions. Let us know what you find and good luck!
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Re: Magneto problems
Your points may be burned or glazed over and not conducting part of the time. If the gap is correct (.013") then they should close tight enough to make good contact. Try cleaning them with a point file and re-setting the gap.
Bigdog
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If you can't fix it with a hammer, you've got an electrical problem.
My wife says I don't listen to her. - - - - - - - - Or something like that!
http://www.cubtug.com
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Re: Magneto problems
Also make certain the spring on the points is in good condition. I have found them weak and or broken and it gives the type of problem you are having.
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1950 Case SC
Re: Magneto problems
Thanks guys for the good info, will take a look at points again, will let you know if I get it running.
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Re: Magneto problems
Ok guys, replaced points, gapped them correctly, got same reading. I decided to play around with ohm meter, testing different parts of mag and points, seeing what readings I got. With the points open, I tested them, and got a resistance reading of 0, or short. This is the first time I have dealt with a magneto, and the first time in 20 years I have dealt with points, so I am no expert, but that reading doesn't seem right to me. Is that the right reading, and if not, what is causing the problem? Thanks, Brett
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Re: Magneto problems
"0" reading when checking for ohms/resistance indicates an open - no continuity. The meter would indicate a short or continuity with an ohms reading.whtwolf97 wrote:With the points open, I tested them, and got a resistance reading of 0, or short.
I have an excuse. CRS.
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Re: Magneto problems
Eugene wrote:"0" reading when checking for ohms/resistance indicates an open - no continuity. The meter would indicate a short or continuity with an ohms reading.whtwolf97 wrote:With the points open, I tested them, and got a resistance reading of 0, or short.
You sure?
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Re: Magneto problems
Yes and no. My Kelvin 400 LE, set on 2K ohms, meter displays "0.L" with leads separated, not touching anything, open. Display reads ".000" when leads touched together or on metal, continuity. Meter set on 20M ohms, only difference from previous readings is the decimal point moved one space to the right.Jim Becker wrote:You sure?
I haven't checked my Klein or any of the other 2 or 3 digital reading meters, or the one analog meter, to see what the display reads with no continuity.
I have an excuse. CRS.
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Re: Magneto problems
What type meter, analog or digital. Analog meter, 0 is a short, and different brands digitalis read different things. Most of mine flash or blink, on open, but read things like .01, etc. on short.
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Re: Magneto problems
Its an analog meter, leads touching it reads 0.
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Re: Magneto problems
0.L on that meter means "open lead" (infinity). A dead short will be .000 with the decimal location depending on which scale you are set on. I would call .000 "zero". Anything close to zero (like .002 or 0.01) is effectively a dead short. On my meter, an open lead displays as the digit 1 on the left side of the display. The blank space to the right makes it obvious it isn't saying 1 ohm.
With most analog meters, 0 ohms is obvious with the needle at full scale and at infinity the needle stays to the left.
When checking resistance at the points and a magneto coil is connected to the circuit, the open points reading will be the resistance of the primary winding of the magneto. The winding may only be a couple ohms. Although the resistance of the coil is low, you should be able to see a measurable difference between open and closed points. With an analog meter, you need to use the lowest scale. If you aren't sure, you can disconnect the coil and the points should clearly cycle between zero and infinity.
With most analog meters, 0 ohms is obvious with the needle at full scale and at infinity the needle stays to the left.
When checking resistance at the points and a magneto coil is connected to the circuit, the open points reading will be the resistance of the primary winding of the magneto. The winding may only be a couple ohms. Although the resistance of the coil is low, you should be able to see a measurable difference between open and closed points. With an analog meter, you need to use the lowest scale. If you aren't sure, you can disconnect the coil and the points should clearly cycle between zero and infinity.
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Re: Magneto problems
I checked it both open and closed and the needle went all the way to the right at 0 both times, but the lowest setting on the meter is x1k so if the resistance is that low it might have just looked that way. I will recheck it without the coil hooked up and see what the reading is. Thanks
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Re: Magneto problems
It sounds like since you retested things that maybe there is a bare wire or a bad insulator on the side of the mag where the lead from the coil goes through the housing causing an intermittent short when it's running. If you isolate the various components you should figure it out. Sometimes it's something simple.
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Re: Magneto problems
Having problems with newly acquired 1951 cub. It has sat prob for 15 years it was my grandfathers so it's been down a while but was running when it was parked. I changed all of my fluids replaced the plugs and wires changed the dist cap and boom I have no spark going to my plugs. I do however have spark coming out of the coil it's just not imputing it into the dist cap. Any ideas of what could be going on?
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