Ford 641 Bad Coil?

[VFMerc]

In attempting to start my 641 (6 volt, + ground) that has been sitting for some time. I have no spark at any of the spark plugs. The battery is new and the machine cranked well. I checked the coil while cranking and there was no spark from the coil center lead. I have removed the coil and checked the ohm reading between the two small terminals obtaining a reading that decreased from 1.0 to 0.00. I understand this indicate no resistance which is good. I then checked the reading from the center port of the coil to one of the small terminals and obtained no change in the meter. It continued to read 1.0. I checked against both small terminals with the same result. Does this indicate that the coil is bad and requires replacement?

I have not yet checked the points yet.

Also, since folks were helpful with the correct part number for NAPA's 6 volt, "isolated" starter relay, if anyone can confirm the correct part # for the appropriate coil, I would appreciate it. The old coil was a NAPA "IC7" and marked "6V No external resistor required, 904".

Thanks,

 

[Jim.ME]

Cleaning the points is generally a first step on a unit that has been "sitting for some time" (How long is this?).

The contact points will often oxidize and form a non-conductive film on them. Often rubbing a piece of uncoated card stock, clean piece of brown paper bag, or even a folded-up dollar bill between the closed points will clean them.

I would clean the points and try it before condemning the coil if it was running fine when parked.

If you do need a coil another one of those should be fine.

 

[Steve Brussell]

In attempting to start my 641 (6 volt, + ground) that has been sitting for some time. I have no spark at any of the spark plugs. The battery is new and the machine cranked well. I checked the coil while cranking and there was no spark from the coil center lead. I have removed the coil and checked the ohm reading between the two small terminals obtaining a reading that decreased from 1.0 to 0.00. I understand this indicate no resistance which is good. I then checked the reading from the center port of the coil to one of the small terminals and obtained no change in the meter. It continued to read 1.0. I checked against both small terminals with the same result. Does this indicate that the coil is bad and requires replacement?

I have not yet checked the points yet.

Also, since folks were helpful with the correct part number for NAPA's 6 volt, "isolated" starter relay, if anyone can confirm the correct part # for the appropriate coil, I would appreciate it. The old coil was a NAPA "IC7" and marked "6V No external resistor required, 904".

Thanks,

Very first thing is to check the points, especiallyifithasbeen sitting any length of time. The quality of ignition points has really gone down nowadays.

 

[VFMerc]

Will do.

 

[VFMerc]

Cleaning the points is generally a first step on a unit that has been "sitting for some time" (How long is this?).

The contact points will often oxidize and form a non-conductive film on them. Often rubbing a piece of uncoated card stock, clean piece of brown paper bag, or even a folded-up dollar bill between the closed points will clean them.

I would clean the points and try it before condemning the coil if it was running fine when parked.

If you do need a coil another one of those should be fine.

It has been sitting for several years now. I’ll clean the points. It had been running fine when it was set aside due to deployments. Thx.

 

[Sean in PA]

I have removed the coil and checked the ohm reading between the two small terminals obtaining a reading that decreased from 1.0 to 0.00. I understand this indicate no resistance which is good.

A 6 volt coil should read approximately 1.5 ohms and not change over time. 1 ohm is too low, and zero is a dead short.

 

[Eman85]

A fast fun and easy test to amaze your friends. Use a test light connected to ground. Turn the ignition on and touch the pointy end of the test ligght to the small terminal of the coil that is powered by the ignition switch and the light should come on, if not trace the circuit. If the light comes on touch the probe to the other side of the coil and turn the engine with the starter and the ignition switch on, the light should blink. If it doesn't blink there is something wrong between the coil and the points.

 

[VFMerc]

A fast fun and easy test to amaze your friends. Use a test light connected to ground. Turn the ignition on and touch the pointy end of the test ligght to the small terminal of the coil that is powered by the ignition switch and the light should come on, if not trace the circuit. If the light comes on touch the probe to the other side of the coil and turn the engine with the starter and the ignition switch on, the light should blink. If it doesn't blink there is something wrong between the coil and the points.

Eman85, Thank you for the information. Today I was able to run the test you recommended. I should say that in response to the other information provided by other members previously, the 641 had set in the barn for 10 years and needed a new starter relay which was installed in the 6 volt, positive grounded system along with a fresh battery. The coil checked out okay, and I have installed a new condenser, points, rotor, cap and wires. The points are gapped to .025 per the manual.

As you recommended I attached the test light to clean ground and then touched the point to the (-) terminal of the coil as that wire runs to the ignition switch. The light within the test light illuminated solidly and fairly bright. I then applied the test light to the other (+) terminal of the coil, placed the ignition switch on and engaged the starter. The engine cranked and although the test light dimmed a bit initially it then brightened but remained illuminated steady while the engine cranked. It did not cycle off at all as far as I could tell. Does this indicate that the points are set too close and the gap should be increased?

I attempted to include the short video (windows media file) of the test light while cranking but can't seem to get it from the facebook page to this board. You or anyone else on this string is welcome to check out the video on my facebook page. Vincent Mercadante (same image/ photo as associated with my name here.

 

[Jim.ME]

Did you clean the points after gapping them by rubbing a piece uncoated card stock, a piece of brown paper bag or even a folded-up dollar bill between the contact points to clean any oxidization and film off them? The film can prevent good contact between them.

The other thing that can affect the points is a bad ground (points to breaker plate, breaker plate to distributor body, or distributor body to the engine).

 

[used red MN]

It did not cycle off at all as far as I could tell. Does this indicate that the points are set too close and the gap should be increased?

No, but it does tell you as Jim pointed out in reply 9 that your distributor is not giving the coil circuit the proper momentary ground signal it needs to run. When the points contacts are closed or touching the terminal on the coil the wire from the distributor connects to should not have power, the points should “ground it out.” With the distributor cap open see if the points are closed. If not turn the fan until they close or give the starter short “bumps” to get it there. When they are closed you have to clean them etc. as Jim mentioned, to the point where when closed with the ignition switch on they will not show power on your positive coil terminal. Open and close them several times to make sure that this turns the test light on and off. This may even mean that the points mounting plate is not contacting a ground properly as Jim said. I suppose I should ask but I assume you looked at a video of how to install the points. Just to double check the rubbing block on the points has to be on the top of one of the bumps on the distributor cam lobe to set the points gap correctly.

 

[VFMerc]

Did you clean the points after gapping them by rubbing a piece uncoated card stock, a piece of brown paper bag or even a folded-up dollar bill between the contact points to clean any oxidization and film off them? The film can prevent good contact between them.

The other thing that can affect the points is a bad ground (points to breaker plate, breaker plate to distributor body, or distributor body to the engine).

Yes Jim. I cleaned the points with card stock. Tomorrow I'll check the position of the condenser wire in relation to the distributor's housing and confirm that I didn't insert it improperly and that the points are opening.

 

[VFMerc]

No, but it does tell you as Jim pointed out in reply 9 that your distributor is not giving the coil circuit the proper momentary ground signal it needs to run. When the points contacts are closed or touching the terminal on the coil the wire from the distributor connects to should not have power, the points should “ground it out.” With the distributor cap open see if the points are closed. If not turn the fan until they close or give the starter short “bumps” to get it there. When they are closed you have to clean them etc. as Jim mentioned, to the point where when closed with the ignition switch on they will not show power on your positive coil terminal. Open and close them several times to make sure that this turns the test light on and off. This may even mean that the points mounting plate is not contacting a ground properly as Jim said. I suppose I should ask but I assume you looked at a video of how to install the points. Just to double check the rubbing block on the points has to be on the top of one of the bumps on the distributor cam lobe to set the points gap correctly.

Will proceed as you and Jim have recommended.

 

[VFMerc]

No, but it does tell you as Jim pointed out in reply 9 that your distributor is not giving the coil circuit the proper momentary ground signal it needs to run. When the points contacts are closed or touching the terminal on the coil the wire from the distributor connects to should not have power, the points should “ground it out.” With the distributor cap open see if the points are closed. If not turn the fan until they close or give the starter short “bumps” to get it there. When they are closed you have to clean them etc. as Jim mentioned, to the point where when closed with the ignition switch on they will not show power on your positive coil terminal. Open and close them several times to make sure that this turns the test light on and off. This may even mean that the points mounting plate is not contacting a ground properly as Jim said. I suppose I should ask but I assume you looked at a video of how to install the points. Just to double check the rubbing block on the points has to be on the top of one of the bumps on the distributor cam lobe to set the points gap correctly.

 

[Jim.ME]

If the copper strap is not making contact with the points spring arm the light will stay on when the points are closed, as well as if one of the previously mentioned areas does not have a ground.

If any of those were touching metal the light should stay out on the distributor side terminal of the coil.

 

[soaked]

Is the item circled in red dots in contact with both the points mounting tab that's bent up ( to hold the points connector stud,) and the points spring? Red arrow points to the tab.
Tab and spring should not be touching...

 

[a49deere]

Is the item circled in red dots in contact with both the points mounting tab that's bent up ( to hold the points connector stud,) and the points spring? Red arrow points to the tab.
Tab and spring should not be touching...

I was wondering if the spring was touching the mounting screw on right as it appears spring is not installed all the way.! Had the same problem on a 420 crawler and the points spring was shorted out. moved it some and problem solved

 

[Jim.ME]

The test light probe on the coil terminal that has the primary wire going to the distributor, staying steadily luminated while cranking with the key on indicates a lack of ground through the points. If any of those wires were grounded the test light would not luminate as the direct ground has less resistance than the test light bulb, that is what happens when the system is working correctly as the points open and close to cause the test light to blink on and off. Points open - test light luminated, points closed - test light will not be luminated.

Without cranking the engine, key on, with the points open the light (on the coil + terminal for positive ground) should be luminated. If you use a screwdriver and momentarily short between the movable arm of the points and the breaker plate (ground for the points) the light should go out.

 

[soaked]

The test light probe on the coil terminal that has the primary wire going to the distributor, staying steadily luminated while cranking with the key on indicates a lack of ground through the points. If any of those wires were grounded the test light would not luminate as the direct ground has less resistance than the test light bulb, that is what happens when the system is working correctly as the points open and close to cause the test light to blink on and off. Points open - test light luminated, points closed - test light will not be luminated.

Without cranking the engine, key on, with the points open the light (on the coil + terminal for positive ground) should be luminated. If you use a screwdriver and momentarily short between the movable arm of the points and the breaker plate (ground for the points) the light should go out.

Hi Jim, of course you are correct. Also, a closer look at what I thought was an extra item, sure looks like light reflecting off the far side of the springs slot. Oops!

 

[Eman85]

Next trick to amaze your friends is to hook your spark tester to the coil wire. With the ignition switch on and the distributor cap off you can manually move the points and the coil will spark across the spark tester.

 

[used red MN]

I will add that it would be a good idea to take a BB sized amount of grease and smear it around the distributor cam. (please limit the amount as specified)