Distributor and resistor questions

Zachary Hoyt · Jun 20, 2012

I am still trying to get my 300 running so I can find out what else is wrong with it. I rebuilt the H4 magneto on my H a couple of years ago with help from Janicholson and others but I have no distributor experience. I have been reading in the archives. I have a 6V coil and I bought a resistor that was supposed to reduce the voltage from the 12V battery to 6V. However when I hook it up it shows 12V both coming into and going out of the resistor and on both sides of the coil, which does not seem right. The wire on the - terminal on the coil is the one that is heading to the battery, does the coil know which lead I am hooking to it or does it not matter? I sanded the points but was not able to get a spark from them. Should I just go ahead and replace the points, condenser and coil or should I start with just one of them? Any advice will be much appreciated.
Zach

mkirsch · Jun 20, 2012

How do you have it wired? The resistor should be between the key switch and the coil.

It's not terribly important to figure it out right now. The coil can stand some 12V abuse.

The coil is somewhat polarity sensitive. If you're doing negative ground, the - should be connected to the distributor.

Don't mess around. Replace cap, rotor, points, condenser.

Bob M · Jun 20, 2012

Zach - If the points are not making contact and grounding when closed, the voltage readings you observed are normal.

To verify try running a temporary jumper from the distributor primary terminal to a good ground. Now turn on the ignition and take your voltage readings again. You should see 12 volts on the ign side of the resistor; approx 5 - 7 volts on the coil side of the resistor and the resistor side of coil primary; and 0 volts on the distributor side of the coil primary. (Don't leave the ignition "on" longer than necessary to take voltage readings - to avoid overheating the coil and resistor).

I'd recommend replacing the points/condenser and see what you get.

----

Incidentally if your tractor is negative ground, the coil + SHOULD be wired to the resistor and the coil - to the distributor. However the coil will work fine with the connections reversed.

buzzinduzzin · Jun 20, 2012

A ballast resistor has very little resistance when it is cool (very little current passing through) so a volt reading will show close to 12 v . Now if the points happen to be closed when you turn on the key then the resistor will get hot, ohms will increase, voltage will drop. Last but not least, some starter solenoids have an extra terminal that is only energized when the starter is engaged. Hook that terminal to the coil side of the resister.

Zachary Hoyt · Jun 20, 2012

Thank you. I have ordered a kit with all of the parts you
mentioned. At this point the tractor is not wired, I have a battery
sitting on the floor with jumper cables to connect it to the
tractor. I had the - cable to the frame rail and the + cable to the
resistor with the other end of the resistor connected to the coil.
I am not sure if that is proper or not based on what you said. I
am turning the engine with the hand crank. The whole tractor
needs to be rewired but if I need to split it I'd rather do that first.
I don't need to be able to move the tractor right now, I'm just
hoping to get it running so I can find the squeal that the PO
described and also see if the hydraulics and IPTO work. I did
drain the oil and look at the seasonal disconnect, which seems
to be in fine shape so I guess that is not the problem.
Zach

CenTex Farmall · Jun 21, 2012

The resistor only "resists" when current is flowing. With no current flowing your readings are normal. Think of current as water flowing and the voltage as pressure. With no water flowing, pressure can build up even through a small restriction.

The battery + should be hooked to the coil + and the - on the coil to the distributor. Grab the end of the distributor where the rotor goes and push/pull on it to see how much play there is. Occasionally you find one with so much play that it defies setting a usable points gap. Should still generate a spark at some point.

Frankly I would just leave off the resistor in this case. It's a little harder on the points but you will get more fire and helps engines with weak compression, oil burning etc.

Hook it up without the resistor for your testing and you can incorporate it later when you do re-wiring.

TheDurk · Jun 22, 2012

If you do leave the resistor off on a 6V coil, just be careful never to leave the ignition on while the engine is not running for any extended period. If the points are closed, the coil will overheat and possibly explode, spraying very hot oil over the side of the tractor and anything else in the vicinity. "Ask me how I know."

Distributor and resistor questions

Zachary Hoyt

Well-known Member

mkirsch

Well-known Member

Bob M

Well-known Member

buzzinduzzin

Member

Zachary Hoyt

Well-known Member

CenTex Farmall

Well-known Member

TheDurk

Member

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