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Farmall & IHC Tractors Discussion Forum
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8v Follow up.....

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Dellbertt

11-28-2005 09:28:45




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I was thinking of putting the 8v on my 300U that I use for snow pushing. But think I will just keep it charged and warm and stay with the 6.

One thought: I had an H with mag for 20 years that never failed to start although sometimes it barely would make one slow turn. If I jumped it with a 12v it would have to start on the first turn or it would turn to fast to start. My point is that if you whip a mag to fast it does not allow the impulse coupler to kick in. Thats why my H always started with slow rev. Hope I made sense out of that.

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R-cubed

11-28-2005 13:51:24




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 Re: 8v Follow up..... in reply to Dellbertt, 11-28-2005 09:28:45  
The impulse mechanism has flyweights that are like on a governor and at a certain speed (they say 250 RPM) they fly out and defeat the impulse catch. Assuming your starter can't turn it that fast it shouldn't be a problem, but I wonder. My Cub has 1/4" of spark on the impulse but doesn't want to start like it did on the battery ignition. I'm beginning to wonder if that 250 RPM is variable or goofed up.

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CNKS

11-28-2005 13:05:13




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 Re: 8v Follow up..... in reply to Dellbertt, 11-28-2005 09:28:45  
I have an H with a mag that I start with a 12 volt battery. I have heard about spinning it too fast -- dunno if I believe that. It doesn't always start on the first revolution, but it does start. I have a friend with a 12 volt M with a mag, I've never heard him complain. On the other hand, if they are well tuned, they will start on the 1st half revolution with a crank.



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Janicholson

11-28-2005 12:57:51




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 Re: 8v Follow up..... in reply to Dellbertt, 11-28-2005 09:28:45  
The impulse coupling on IH mags work the same as on other equipment. (as John T indicates) there is a spring wound speed increaser in the magnet.
JimN



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JT

11-28-2005 11:22:20




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 Re: 8v Follow up..... in reply to Dellbertt, 11-28-2005 09:28:45  
Dellbert,
I do not want to sound argumentative, but the impulse on a mag retards the spark during starting. It does not make it go faster as it passes the magnet to get a hotter spark. That is why you can hand crank an engine. If it did not retard at starting it would kick back and make you hurt real bad, becasue most engines fire before top dead center and if it did not retard the spark it would fire as you are still coming up on the compression stroke. At least that is my understanding of how a mag works. Most people around here used 8V batteries to compensate for a starter in poor condition. Normally if you keep the commutator clean and brushes in good shape you never need anything but 6V to make 'er start.

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John T

11-28-2005 12:08:29




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 Re: 8v Follow up..... in reply to JT, 11-28-2005 11:22:20  
Hey JT, Im NOT here to argue either just to try n help people the best we can. I agree definitely a Mag retards the timing when youre starting her, otherwise when shes slow cranking she would fire like 20 degrees Before TDC causing her to kick the flywheel backwardsssss s and thats a definite NO NO. Buttttt tt then when the wind n trip assembly stops functioning (centrifugal force prevents dogs from engaging) the run time advance takes over which allows them to fire maybe 15 to 25 degrees (depends on adjustment) Before TDC as needed, and the rotor is turning at straight speed same as the driver NO WIND UP N TRIPPING OF A SPRING THEN LIKE AT SLOW RPM

HOWEVERRRRR RRR (Rememeber Im more familiar with JD Mags like the Wico C and X or AP NOTTTTT the Farmall Mags) I do know for a fact and REGARDLESS what brand of a Magneto, THAT AT SLOW CRANKING SPEEDS THE ROTORS MAGNET DONT PASS BY THE COIL NEAR FAST ENOUGH TO INDUCE SUFFICIENT VOLTAGE INTO THE COILS PRIMARY Sooooo ooooo o thats how n why when you turn the mag slowlyyyyy yyyy its not initially turnign the rotor, but it turns to wind a spring that winds up n then releases to rapidly whirlllll ll the rotor at a fast speed past the coil so it does go fast enough to create a good spark.

A battery powered coil ignition uses battery energy n voltage to power up the coil while a Magneto creates its own energy by passing a magnet (rotor) past a coil of wire (the coils primary) to induce voltage and the faster the magnet passes by the coil the greater the voltage BUTTTTT at real slow passes, theres not enough voltage induced, THEREFORE it needs to wund a spring up n trip it to rapidly whirl the magnet past the coil while its being slow RPM started.

I hope some of the good gentlemen familiar with the Farmall mags will weigh in here to show me right or wrong, but until then "Thats my story n Im stickin to it" lol

Thanks JT, best wishes n God Bless yourself and all else here. Hopefully we can all learn from this fun discussion, thats why were all here and I can learn about farmall mags if they are indeed different concerning how their spring assembly works if its different then the Mags Im familiar with????? ?????

John T, retired electrical engineer

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John T

11-28-2005 10:03:26




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 Re: 8v Follow up..... in reply to Dellbertt, 11-28-2005 09:28:45  
Del, thanks for the feedback, its always fun to hear what happens. I understand what youre saying on the mag. They are designed with the spring wind n trip impulse mechanism cuz at slow cranking RPM the magnet doesnt pass by the coil fast enough to induce sufficient voltage. Thats why n how winding the spring lets em trip n whirl the magnet fasttttt tttt by the coil for a good spark while shes cranking. Then theres the critical RPM at which centrifugal force disables the wind n trip and youre running at engine RPM cuz at that RPM (250 on John Deeres on Farmall???) the speeds fast enough to induce sufficient coil voltage for a good spark. HOWEVER its still the faster the more energy, sooooo ooooo if she cranks so fast the mag just is barely at the critical RPM the spark may be weaker then if the spring wind n trip were allowed to function????? ?? BUTTTTT TTTTT TTTTT I dont see any battery n starter really making her crank all that fast (if its like 250 RPM????) so Im just not sure if that explains what you seem to be proposing????? Heck if I know lol I dont know at what RPM the Farmall mags wind n trips stop working, sorryyyyy yyy.

If you stay at 6 volts just have a big heavy rated battery and 00 Gauge cables n she ought to perform reasonably well.

Best wishes

John T

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El Toro

11-28-2005 09:57:07




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 Re: 8v Follow up..... in reply to Dellbertt, 11-28-2005 09:28:45  
Using 10wt oil would help starting in the cold weather. I would switch back to 30wt in the summer. Don't jump start at the battery. Connect
at the starter. Hal
PS: Using a block heater will make it crank & start easier too.



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