where does the spark go?

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northwoodsguide
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where does the spark go?

Post by northwoodsguide » Sun Sep 25, 2022 10:36 am

I could not restart my jd 420 after pulling up in the yard to pull the winch off. Some sort of electrical problem and I decided to change out the coil as it was looking a little worn away with rust. Did not start immediately but while fiddling with it, it all of a sudden started working fine. I buttoned up and drove the machine a hundred yards back to its stall in the barn. When I went to start it a few days later, the electrical was gone again. I assumed it was. not the coil in the first place but some sort of intermittent electrical connection. I bought and installed new points, condenser, rotor button and wires. Still does not start, here is the present condition:

--I may have screwed up the timing as I have been trying dozens of different strategies to isolate the problem as well as pulling the distributer and cleaning it up.

--I have a spark at the points.

--When I disconnect the secondary wire and directly connect it to a spark plug, the engine starts right up and runs on that one cylinder. When I connect the secondary wire back into the distributer cap, all spark disappears.
Question 1; doesn't this tell me that the timing is within the ballpark? Wouldn't you think the engine could not run unless the points were releasing at approximately the correct time to stimulate the secondary coil? I had a mechanic tell me that the coil will fire as long as the engine is turning over but that seems to go against everything I understand about the physics here. Doesn't that coil have to have the points break in order to collapse the primary field and induce the secondary coil to collapse as well?

-- I have an indicator that I install in the spark plug wires that lights up when a spark is fired. As stated above, when I disconnect the secondary wire from the spark plug and put it back in the distributer cap, all spark disappears. I know their is spark across the points. When the secondary wire is directly connected to a plug, I can take the distributer cap off and literally watch the points firing as the engine runs on its one cylinder.
Question 2; Doesn't this tell me that the issue has to be somewhere in the distributer cap? I have gone over the cap carefully and cannot see anything that might be a problem.

-- in desperation, I reinstalled the old distributer cap and rotor button with same results as above. I did not put the old wires back on.

Question 3; does anyone have a strategy for me to pursue here? I have to say, I am out of ideas on what it could be.
JD 420c / 56 Willys utility truck/ 56 Willys CJ3B/ 49 Dodge pilothouse B10.
Located in Central Maine

northwoodsguide
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Re: where does the spark go?

Post by northwoodsguide » Sun Sep 25, 2022 10:53 am

Forgot to mention that the electrical system is a 12 volt, negative ground.
JD 420c / 56 Willys utility truck/ 56 Willys CJ3B/ 49 Dodge pilothouse B10.
Located in Central Maine

northwoodsguide
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Re: where does the spark go?

Post by northwoodsguide » Sun Sep 25, 2022 12:16 pm

Also forgot to mention that I bought a new distributer cap and tried that as well.
JD 420c / 56 Willys utility truck/ 56 Willys CJ3B/ 49 Dodge pilothouse B10.
Located in Central Maine

Jim B
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Re: where does the spark go?

Post by Jim B » Sun Sep 25, 2022 5:38 pm

Something to be aware of. If you tell some parts stores you have a 12volt system, they will give you a cap for a 2-cylinder Waterloo engine (which will fit a Dubuque engine just fine as both use Delco distributors). Did you compare the old and new distributor caps? A distributor cap doesn’t care about 6 or 12 volts. The original 6-volt cap is needed for your distributor to match the lobes that operate the points.

Sounds like you may be out of time for one thing. Here is a way to check to see if you are close on timing to start with.

Make sure the crawler in neutral.
Remove #1 plug. Hook its wire to it and ground the plug so you can see the tip.
Put your finger or thumb tightly over the #1 plug hole in the head.
Ignition switch on and crank the engine over.
You should see the spark at the plug when your finger is pushed off the hole by compression if the timing is close. If it isn’t there is a chance you put the distributor back out of time.
Next step is bump it over until it starts to push your finger off the hole and stop.
Remove the distributor cap and see where the rotor is pointing. It should be approaching the # 1 contact in the cap.

northwoodsguide
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Re: where does the spark go?

Post by northwoodsguide » Sun Sep 25, 2022 6:06 pm

Thanks for the neat trick to find the compression stroke. I will try it tomorrow. What was your opinion on the coil statement ... wouldn't the timing have to be close to correct if I can run the engine on one cylinder directly off the coil?

Regarding the distributer cap; Thanks for that info as well, am sure it will come in handy at some point but I have looked at the new cap very closely and cannot find any differences. I also put the old cap back on with no change in results.
JD 420c / 56 Willys utility truck/ 56 Willys CJ3B/ 49 Dodge pilothouse B10.
Located in Central Maine

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jimmydiesel
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Re: where does the spark go?

Post by jimmydiesel » Sun Sep 25, 2022 7:27 pm

northwoodsguide
Is there any chance you have the spark plug wires reversed. If you hook one of the spark plugs up to the coil it will fire at the top of the compression stroke and at the top of the exhaust stroke. If the spark plug wires are reversed ( 180 degree’s out ) both cylinders will be firing at the top of the exhaust stroke.
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northwoodsguide
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Re: where does the spark go?

Post by northwoodsguide » Mon Sep 26, 2022 9:24 am

Don't believe I have them reversed, but will check against the service manual anyways. Wouldn't I still get a spark through the spark wires, just at the wrong time? I am getting no spark when I hook up the distributer cap to the coil. Doesn't the fact that it will run on one cylinder when directly hooked up to the coil indicate that the points are breaking at the proper time, when the cylinder is at TDC. How would this explain the presence of spark when the secondary coil wire is directly connected to the cylinder and the absence of spark when it is hooked back up to the distributer?
JD 420c / 56 Willys utility truck/ 56 Willys CJ3B/ 49 Dodge pilothouse B10.
Located in Central Maine

Jim B
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Re: where does the spark go?

Post by Jim B » Mon Sep 26, 2022 9:50 am

Your coil is generating a spark. The points are working. The coil is working. If the terminal contacts in the cap are not in the proper place (so the rotor is pointing at them) when the points open and a spark is generated, you will not have spark at the plug wires. Do the check I suggested to see where the rotor is pointing when the coil makes the spark.

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Stan Disbrow
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Re: where does the spark go?

Post by Stan Disbrow » Tue Sep 27, 2022 4:46 am

Hi,

New coil you say? 12v one?

Was the old one an original 6v one?

If so, did you remove the resistor?

If not, then you will have enough high voltage for a direct coil to plug connection but not enough to make it thru the rotor and cap. I have seen this before. Found by using a Hi Voltage probe (which most folks do not have).

Also, beware of carbon core high voltage wires. AKA resistor wires used to reduce noise in car radios. They tend to become lossy over time. I have also seen this before. Same sort of issue. Not enough HV at the plugs or a plug.

Yet another way to lose spark is a bad spot in the insulation of a HV wire. Like the coil to cap wire. Might need to eyeball that in the dark.

Stan
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Buckhorn
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Re: where does the spark go?

Post by Buckhorn » Tue Sep 27, 2022 2:59 pm

It may sound strange, but you don't have the cap on 180 degrees out do you?
Just a thought as to why spark isn't getting through.

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jimmydiesel
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Re: where does the spark go?

Post by jimmydiesel » Tue Sep 27, 2022 3:06 pm

Or have the distributor in 180 out. Ether one would put the rotor on the wrong side. Do the check Jim B suggested.
440 ICD 602 Blade 3Pt.hitch.
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440 ICD 604 6 way Blade Carco winch
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