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Farmall & IHC Tractors Discussion Forum
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Farmall H4 Magneto troubles - help please

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tirediron

04-14-2007 00:00:33




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Okay, I"ve finally got the mag apart, it"s cleaned, painted and reassembled with new points, gasket and condenser. All should be good right? Not so much... All darky, so sparky.

(Mine is a later H4 where the coil-grounding strip does not require soldering) IH Mag Manual says that there should be two coil insulators which I do not have. The picture is very dark, can anyone provide further info on these?

The bottom line is the primary winding is grounded, ergo, no spark. I"m assuming that the coil insulators would rectify this problem, but I"m not sure. Any help would be very much appreciated.
Tks
John

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Old Gomer

04-15-2007 21:21:40




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 Re: Farmall H4 Magneto troubles - help please in reply to tirediron, 04-14-2007 00:00:33  
Be sure the little clip that grounds the condensor case is in place and held down by the screw.



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Bob

04-14-2007 05:49:44




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 Re: Farmall H4 Magneto troubles - help please in reply to tirediron, 04-14-2007 00:00:33  
The "coil insulators" likely are a little extra insurance againt high voltage "flashover" from the coil to the case, and their abscence is probably NOT your problem.

The coil primary IS grounded at one end and has low resistance, making it APPEAR grounded, even at the points/coil end.

With the coil's primary lead temporarily disonnected from the points/condensor, check to see if there is still a short to ground from the insulated breaker point, with the points "OPEN".

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tirediron

04-14-2007 11:30:50




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 Re: Farmall H4 Magneto troubles - help please in reply to Bob, 04-14-2007 05:49:44  
D'ohhhhh hhhh... *Smacking self on forehead* That's what I get for using that stupid digital multi-meter. Thanks!

Okay, so, with proper measurements made, here's what I get:

Ground to Primary .5 Ohms

Ground to Secondary: 9.4 K Ohms

Primary to Secondary: 9.4 K Ohms

I'm assuming this means it's hosed?



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Bob

04-15-2007 00:21:28




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 Re: Farmall H4 Magneto troubles - help please in reply to tirediron, 04-14-2007 11:30:50  
Off the top of my head, those numbers don't look too bad, but I've been up for nearly 20 hours, working, and would need to look at the manual to be sure!

You can take a look at the Blue Ribbon Mag Service Manual at the Cub Collectors website.

You'll have to "cut" this link, and "paste" it into your browser, as the YT site does NOT allow it to be posted as a "hot link".

Link

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tirediron

04-15-2007 10:35:53




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 Re: Farmall H4 Magneto troubles - help please in reply to Bob, 04-15-2007 00:21:28  
I"ve got the Blue Ribbon book, unfortunately all the discussions on testing are using the old style "growler" and not a modern multi-meter, so there are no (that I could find) resistance values.



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Bob

04-15-2007 11:23:57




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 Re: Farmall H4 Magneto troubles - help please in reply to tirediron, 04-15-2007 10:35:53  
The Cub Manual Site seems to be down right now, I was going to take a look now that I've had some sleep... Your numbers look pretty normal to me.

The trouble is, a coil cannot be 100% tested for operation with an Ohmmeter. A shorted turn or two will not change the Ohms reading much at all, but will use up the energy needed for a HOT spark as HEAT inside the coil.

Besides the possibility of a bad coil, is your "impulse" working properly, and have you checked the "timing" of the cam to the armature? (It's in the manual).

Since this post is now a couple of pages "back", if I can be of any more help, start a new thread, or email me.

bigcoulee@hotmail.com

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Red Dave

04-14-2007 07:32:00




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 Re: Farmall H4 Magneto troubles - help please in reply to Bob, 04-14-2007 05:49:44  
That's good advice from Bob. It is very easy to accidentally ground the coil at the condenser connection. Not much room in there to work.



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John T

04-14-2007 06:51:03




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 Re: Farmall H4 Magneto troubles - help please in reply to Bob, 04-14-2007 05:49:44  
Bob, as you know Im NOT an IHC Mag man buttttt t I'm learning n think your post was great. A typical Mag primary may be only like 0.5 ohms so I sure agree it appears almost a short on either the open (to points) end or the grounded end. At my Wico talks I tell em to use a good ohmmeter set on the R x 1 scale with a lead to ground and the other to the points and when closed it should read near zero ohms but when open still only like 1/2 to 1 ohms or so. If an open its obviously an open coil primary but if it stays a dead 0 ohms short even with the points open, I tell em to suspect a bad/shorted condensor (unhook n try it) or the points spring may be shorted or the point to coil wiring etc. has a short.

I may get an IHC Mag n play with it lol

John T

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A. Bohemian

04-14-2007 08:28:01




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 Meanwhile, Back at the Old Thread in reply to John T, 04-14-2007 06:51:03  
John, I just this morning got a chance to finish the thread which rolled off the page yesterday. I think you were replying more or less to me when you wrote the following:

Quote: "I got to thinkin I agree with your notion in a way, its just that when you say 35 RETARD I think you meant she retards 35 BEHIND the run time advance NOT that she ever fires 35 AFTER TDC sooooo ooo lateeeee eeee, which is far to slow to ever start fer sure, although she could run poorly I reckon??"

Yes, that is what I meant, but not what I said. Thirty five degrees after TDC is very, very retarded indeed!

What concerns me, though, is that I am fairly certain that SOMETHING must be timed so that at hand cranking speeds, the spark must occur well past top dead center for safety reasons.

Ah, but what is "well past?" I don"t have a clue; but maybe say six or seven degrees?

Remember, with a centrifugal or other mechanical advance, the timing would only be this retarded for the FIRST cylinder to fire, and would come quickly up to where it needed to be, at or before top dead center (but not by much, since we are usually starting at fast idle-type speeds).

But pity the poor lone Model T driver in cold weather, who must sprint back to the driver"s side of the car and yank down on the spark before she dies...

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John T

04-15-2007 08:06:00




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 Re: Meanwhile, Back at the Old Thread in reply to A. Bohemian, 04-14-2007 08:28:01  
Hi there again AB, were still havin a fun discussion fer as Im concerned. Stilllll ll as far as I know on other models, but for dern sure on the Wicos, theres ONLY one adjustment/setting for the Impulse start time. On the Wico its set by adjusting the stop plate which determines when the impulse engages the spring winder upper (cuz the engage dogs arent sucked back in by centrifugal force at 250 RPM) plus the rotational adjustent of the mag itself.

I SURE AGREE its dangerous for them to fire BEFORE TDC at cranking buttttt tttt on the Wico at least theres only one adjustment n one option to set that (but 2 ways it can be adjusted)

The Wicos at least have NOOOOO sort of RPM dependant centrifugal advance curve, itsd EITHER start or run.

Again, I DONT KNOW BEANS ABOUT IHC MAGS buttttt ttttt still pretty sure they are the same as far as having ONLY a start n run time with no in between and one simply has to NOT set em to fire BTDC or risk an injury.

Im at O Hare Airport waitin for the daughter, see yall later tonight.

Take care AB, I really enjoy this sparky chat

John T

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