I would like confirmation on the way I tested my C100 Coil

[Jrblanke 885]

I think I have a bad coil. Please see the pictures below:

 

 

Main circuit - 7,530 ohms

 

Secondary circuit - 4.2 ohms

 

Based on the threads I found on here using the search function, the main circuit should be around 10,000ish ohms, and the secondary circuit should be 8ish ohms. Please correct me if I am wrong.

 

James  

[squonk 42,833]

What scale is that meter on? In 30 plus years in the Auto repair /parts biz I rarely saw one of those old single post coils go bad unless they burnt up. You can get an IC64SB from Napa for 25 bucks and just replace it. Looks by the readings it's bad. Another way to test things is to hook up everything and put a 12v test light on the positive terminal of the coil. Turn the key on. If it lights put it on the negative and crank the engine. It should flash. IF it does you have a bad coil,coil wire or plug. If it doesn't flash, you have a points problem.

Edited March 15, 2014 by squonk

[Save Old Iron 1,568]

what is the engine doing to make you suspect a coil problem?

[Jrblanke 885]

The engine is turning over, but not firing. I removed the spark plug, sprayed some starter fluid into the cylinder, then put the plug back in and turned it over. It didn't fire, so I believe it is a spark problem instead of a fuel delivery problem. 

 

I just started checking parts, and the things I know the least about are the points and the coil. 

 

I am going out now to test the plug and plug wire. (by swapping them out with parts from my running engine)

What scale is that meter on? In 30 plus years in the Auto repair /parts biz I rarely saw one of those old single post coils go bad unless they burnt up. You can get an IC64SB from Napa for 25 bucks and just replace it. Looks by the readings it's bad. Another way to test things is to hook up everything and put a 12v test light on the positive terminal of the coil. Turn the key on. If it lights put it on the negative and crank the engine. It should flash. IF it does you have a bad coil,coil wire or plug. If it doesn't flash, you have a points problem.

 

 

For the main circuit I had it set on 20,000 ohms (20 Kohms), and for the secondary I set it for 200 ohms. 

Edited March 15, 2014 by Jrblanke

[Ed Kennell 40,798]

 The coil is the last part I would change.  I would check  for 12v at the + coil terminal with the switch on run,  then  clean and check all the terminals to points and condenser  , then clean and set the plug and points.   Then install a new condenser. 

                                                                                               

[squonk 42,833]

I'm going to guess your coil is good and you have an issue with 12 v getting to the coil

[pacer 3,176]

Did you check to see if the spark plug was firing? thats the very first thing I check when something like this happens. Remove the plug, put the plug wire back on and lay the plug on some engine surface that it can ground on and with the key on rotate the engine - you should get a very noticeable spark. If not change or clean the spark plug - If you been put-puting around much at idle the plug will foul easily. Next likely culprit is the points, they can get a glaze on them and will not contact - drag some fine sandpaper through them to break that glaze and see if the plug fires, if does best to replace the points but if fires go ahead and finish what you need done and replace the points later. Next is condenser and coil and they are the least likely to be the problem. The plug and points are probably the most likely candidates and very easy to check - of course there are many other possibilities, but get these cked first.

[Save Old Iron 1,568]

And be sure 12 volts connects to the + side of the coil.

Confirm the condensor is connected to the - side of the coil along with the points wire.

[Jrblanke 885]

Update for this situation is that the plug is good. Also, I removed the points and replaced them with new points. The old points did have burrs on them, but I don't think that was the problem. I believe I am not getting 12 volts at the coil. 

 

Once I charge the battery back up, I will bypass all the wiring and connect the coil directly to the battery. 

[Save Old Iron 1,568]

I believe I am not getting 12 volts at the coil. 

 

Have you measured the + terminal with your meter?

It's a quick check before tearing apart the ignition switch wiring.

[Jrblanke 885]

Measured the battery. It has 12 volts. Measured the voltage at the coil (placed one multimeter lead on the coil terminal, and one to ground) and had 12 volts. 

 

I confirmed there is no spark. I put new points on it (I am not sure if I have to set the dwell on them, they don't look adjustable like the ones on my 73 chevy). 

 

So back to my original question, did I test my coil correctly? The top picture is with the multimeter set to 20,000 ohms. The bottom picture is with the 20ohm setting. 

[pacer 3,176]

The points ARE adjustable and will have to be set with a feeler guage at .018-.020, look at your old points closely and you should see. Rotate the motor til the points open - if they dont open (which may be the case) then watch the pusher arm that comes out of the block til it moves outward to its farthest point - then loosen the one screw just slightly, this is important to give some 'drag' allowing the points to not slip back closed. use a flat blade screwdriver and find the best place to do a gentle twist and move the points to get the setting with the feeler guage. Its kinda hard to explain, but I think youll see that its a quite simple procedure when youve figured it out.

[squonk 42,833]

If those points don't open and close, all the voltage in the world at the coil won't do you any good. You need to interrupt the primary circuit to induce the high voltage in the secondary windings to create a spark