Dead 47 Cub

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Ray D
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Dead 47 Cub

Postby Ray D » Sun Mar 01, 2015 11:24 pm

I'm a newbie to the site requesting help with my dead 47 Cub. It is a standard Cub with a magneto. It ran well for months. Now it suddenly acts like there is no battery connected. I verified the battery is charged and the cable to the starter is good. The ammeter fuse in good. I even tried hand cranking it without success. Can a bad magneto cause a complete failure where it will not even crank? I expected if the mag was a problem, it should still crank the starter motor but not start - is that valid? Also bypassed the on/off switch without success. Any ideas are appreciated. Thanks. Ray

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Re: Dead 47 Cub

Postby Posco » Mon Mar 02, 2015 12:20 am

Interesting. I just replaced a bad kill switch on my Cub. Different problem, though. It wouldn't kill the tractor so I had to shut off the fuel and wait for it to die.

I had a bad wire leading from the mag to the distributor. No fire to the distributor. Worth checking. More seasoned hands will be along shortly.

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Re: Dead 47 Cub

Postby randallc » Mon Mar 02, 2015 6:07 am

Welcome to the forum from Arkansas. When you say won't crank - I assume you mean that it will turn the motor over but will not fire. First think to check is fuel in the carb. Then check to see if you are getting spark to the spark plugs. Is the inpulse working? If the inpulse does not work there will be no spark. If the coil goes out in the Mag, it won't run. If the points go out it won't run. If you're getting good spark, then it is probably fuel related. So a little more information is needed.
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Re: Dead 47 Cub

Postby tmays » Mon Mar 02, 2015 6:22 am

Sounds like bad starter or starter not grounded. Possibility that starter has not retracted from flywheel, but I'd think you would hear something if this is the case. Remove starter and clean mating surfaces well. While you have starter off, connect it to battery and see if it spins. If it does, replace starter and try again
Edit: bad mag will not cause it to not turn over. But it should hand crank with mag without battery. Since it won't, more needs to be done. Mag may need serviced. Kill switch may be bad. Could be timing it even fuel related as in no fuel to carb. I'd begin with starter.
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Re: Dead 47 Cub

Postby challenger » Mon Mar 02, 2015 6:32 am

Your use of the term 'crank' confuses me. Do you mean the engine turns over but does not fire or do you mean the engine will not turn over at all even when you use the hand crank?

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Re: Dead 47 Cub

Postby Eugene » Mon Mar 02, 2015 8:38 am

Voltage drop test your fully charged battery while trying to crank over the engine.

Or, take the battery to the auto parts store for testing.
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Re: Dead 47 Cub

Postby tmays » Mon Mar 02, 2015 9:38 am

Eugene wrote:Voltage drop test your fully charged battery while trying to crank over the engine.

Or, take the battery to the auto parts store for testing.

Agree with Eugene. Also, you said cable to starter is good. Visual inspection is not enough. I would remove both cable and clean connections good.
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Re: Dead 47 Cub

Postby John *.?-!.* cub owner » Mon Mar 02, 2015 10:18 am

Couple questions. would the engine turn over with the crank? If yes, but would not turn with starter, check the ground lead. They were originally attached to the battery box, and the boxes got rusty where they bolted to the tractor and lost the connection. If you have jumper cables use them from the ground to a starter bolt and hot to the starter lug and try it.

If you can't turn it with the crank the starter may be locked into the ring gear. If that is the case, simply loose the starter bolts a turn or so, put tractor in 3rd and rock rear wheel. Put back in neutral, tighten bolts and try.
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Re: Dead 47 Cub

Postby Ray D » Mon Mar 02, 2015 11:39 am

Wow! All great points. Thanks Gents. I'll try to clarify the issue better and please point out any problems with the logic in my approach. Battery holds the proper charge but has not been load tested - would expect engine to fire up on hand cranking if the battery was the only problem source. The main issue is the engine will not turn over via the starter system so I hand cranked it. Engine turns freely via hand cranking but will not fire. Hopefully that also means the starter is not locked. Have not checked the fuel system (has adequate gas) since getting the engine to turn over should precede a lack of fuel issue. Have verified proper voltage to the starter via the cable so don't expect a grounding issue with the cable but will double check it. Unsure on the kill switch. I disconnected the wire from the switch to the mag without success - if the switch was bad, wouldn't it still allow the engine to crank but just not fire up? Will also try bypassing the connecting points using the suggested jumper cables.

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Re: Dead 47 Cub

Postby tmays » Mon Mar 02, 2015 12:02 pm

Since engine turns with hand crank, starter is not locked in ring gear. One of three possibilities: bad battery, bad starter, or not a good connection between battery and starter.
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Re: Dead 47 Cub

Postby Posco » Mon Mar 02, 2015 12:30 pm

Ray D wrote:- if the switch was bad, wouldn't it still allow the engine to crank but just not fire up?


Yes. You would either have to ground it out or turn off the fuel to shut the tractor down when it does start. I suppose it could be a dozen little things causing you grief and you'll just have to go one by one until you stumble on to the problem. You'll learn a lot in the process, I know I did.

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Re: Dead 47 Cub

Postby staninlowerAL » Mon Mar 02, 2015 3:40 pm

Has there been any modifications to the mag (external coil) added? Does the points arc when they open and close while hand cranking? If you do not have a spark AT THE POINTS as they open and close, it will never start. If no spark, try cleaning and setting the points, .013 and then move on to the plugs and see if each one is firing as the engine turns with the hand crank. If your system has not been modified, the starter only turns the engine for cranking, the fire for running the engine comes from the mag coil, not the battery.

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Re: Dead 47 Cub

Postby robertst » Mon Mar 02, 2015 9:13 pm

Have you checked kill switch connection at mag and wire going inside of mag to be sure it isn't grounded out,if it is grounding out that will kill the mag.

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Re: Dead 47 Cub

Postby ecbrewster » Mon Mar 02, 2015 10:45 pm

It sounds like you have two problems, both independant of each other. Regardless of the starter issue, you should check for spark during hand cranking and you should also hear the impulse coupling on the mag. It should give a good loud clack during hand cranking. If you don't hear the "clack", try some light oil in the oil cup behind the mag. If you can verify a spark, disconnect the fuel line at the carb and see that you have a good flow. If you have spark, timing is correct and fuel flow to the carb, you may need to clean the carb. Good luck!

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Re: Dead 47 Cub

Postby Ray D » Tue Mar 03, 2015 2:33 pm

Problem appears solved. The dead 47 is now running. Problem was the corrosion between the battery box and the frame. It made the entire tractor dead. One day it was running, a week later - nothing. Thanks to everyone that helped with suggesting possible techniques to identify the issue and a special thanks to John *.?-!* who suggested I check the battery box connection for corrosion. :thanx:


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