VCCA Home Forums TECHNICAL - GENERAL Electrical - 6 volt Bad Coil on my '34?

Today my '34 Standard was idling nicely in the driveway (thankfully) when it suddenly stopped running. Thought it was out of gas but discovered it had no spark at the distributor.
I have good juice at the ignition terminal on the coil. The starter turns over fine. The primary (small) wire from the coil to the distributor has continuity. Checked points which seem good and right gap. But put new set in. Still no spark. With the ignition on I have power to the coil as I said but none at the distributor side terminal.
So I'm thinking the coil is bad. It is one of the old original designs. I checked resistance of the primary coil circuit which is 4 ohms and the secondary has 6 ohms. I don't know what that means but my mechanics handbook says to check that. So what have I overlooked, not checked, or do I have a bad coil? Automotive electrics is not my strong point.

Thanks ahead for helpful replies!!!!!!!!!!!!!

Coils are almost never the cause of a quick failure. Points are the most suspect, then the condenser second, rotor/distributor cap before coil. That being said I have had problems several times with foreign built modern 6V coils over heating and failing. I pour water to cool them and they work just fine until they overheat again. The overheating always due to long upgrade at slow engine speed in warm to hot weather.

I'm fairly certain the rotor, cap, and points are ok. I just used the "search" link and with your suggestions think the condenser is the problem. It is old. Do I ask for a 6 volt condenser at
the local parts store or all condensers the same? Thanks for your reply.

Ask for a condenser for a '54 Chevy. If they don't have one then get what ever they have that has a long enough lead wire.

I agree....it sounds like you have a bad condenser.

It is always a good idea to have two or three spare condensers in stock as well.

Thanks for help. Will let you know how it works out.

Decided to put in a new condenser first to rule that out. Still did not start. I took coil out and checked it. Showed about 1.7 ohms on primary and 8000 secondary. I have another much newer 6 volt coil that shows more like 20,000 ohms on the secondary. Mechanic friend said 8000 probably OK though. What do you think? He thinks I may have a short somewhere.

So I realized the bolt through the distributor that holds the points and primary wire may be shorted. This after I changed the points and condenser. It had a bunch of rubber/paper washers when I took it apart. Evidently 2 of these fit between the bolt and the housing. I put it back together just as it came apart (I think) but may not have it fully insulated. While I had the bolt out I checked the new condenser (using ohmmeter to charge/discharge) and the new condenser, made in mexico, did not take a charge. So I'm taking it back tomorrow.

Wondering if 20,000 ohms would burn up the points if I put the newer coil in.

Again, any suggestions, instructions, etc. are greatly appreciated.

Insulate the terminal stud on the distributor correctly and replace the new defective condenser with one that will hold a charge and then get back to us with the results.

I will do just that. But I am wondering if all the washers are something someone cobbled together or if that was the way it came in 1934. Seems archaic even for that era.

It sounds like maybe a few parts were added to the terminal stud.

The '34 is running fine again. The condenser was the problem. Old coil is still in and no problem. A new set of points I installed were a problem. So that is where I was hung up. After putting the old points back in it started right up.

As I usually do, I made a half hour job last a half day but at least I have gone through the whole ignition from switch to plugs. And I have backup parts in the trunk.

Thanks for your help!!!

Glad that you got the old girl running again!

One thing to always try to remember is "If you found a problem after some change was made, even if the change is to added a NEW part, then it is likely that the change contributed to the problem." "New does not mean functional."

On your coil question; typically for six volts, the primary should read between 1.43 and 1.58 ohms resistance. If there is zero resistance, there is a short in the coil and it is not functioning. If there is infinite resistance, there is a break in the windings and the coil is not functioning.

On the secondary, the coil should read between 6,000 ohms and 8,000 ohms, while other coils could read as high at 15,000 ohms. I tested my 1932 Chevrolet coil today to use as a comparison. I first checked the coil on my coil tester and it was rated at 60 to 70 per cent. In doing that I knew that I had a good coil to use as a sample. On checking the primary resistance, my coil tested out at 1.4 ohms. On the secondary, the coil tested out at 9,600 ohms.

Your readings on the primary as well as the secondary are right where mine were. Thanks for the info.!

You bet and glad to help you out!

Went to get the '34 out of storage and no start just as last Dec. Again no spark. Replaced the old coil with new one plus new condenser. Still would not spark. Did see a very very weak spark at the points, none at the plug. None now. Took condenser out, cleaned it's mounting "strap" and point of attachment on distributor to be sure of good ground. Started up and I drove it home. Started it this morning to warm up for an oil change. Started easy, ran fine, then died. Again no spark. Checked points, changed rotor, checked for continuity in small wire from coil to distributor and its OK. Tried again, ran for a bit then died. Again no spark. Must be a short or bad ground or ???.

The plug wires are new, coil is new, rotor is new, points are new, condenser is new. Distr. cap looks fine and is fairly new but I have not put a new one I have in yet. The problem was same with the old ones.

I need some suggestions for what and how to check for other problems. Any advice would be GREATLY appreciated on the intermittent loss of spark !!!

When ever there is no spark or weak spark, the first thing to check is power to the coil. Turn on the ignition switch, remove the positive lead to the coil and strike it against a ground. There should be a spark. If no spark there is no power to the coil.

Second is the points points. Open and close the points when holding the end of coil wire to the distributor approx 1/2" from a ground. Any spark? move the wire to approx. 1/4" spark now? Does it make a audible "snap"? Now put a piece of paper or plastic between points and short across the points with screwdriver, knife blade or piece of metal. Do you get a stronger spark than before? If so clean the points or replace them. I don't care that they might be new. They still need to be cleaned or replaced.

Next is the condenser. Make sure it has a good ground to the outside case. A bad ground will only produce a very weak spark. If there is a ground then put on another condenser.

The last part to check is the coil. Rarely are they bad compared to other ignition parts. Check the resistance of the primary and secondary coils. If the coil checks well or the engine runs for a while and then quits pour cold water on the coil. Does the engine now run?

Chipper

Thanks for the reply. I have basically checked all you mention and replaced all the components. But will go back and recheck per your instructions. I'm still suspicious of a bad ground on the condenser. It is really difficult to install as it is below the distributor and the short screw is difficult to get started and tightened. My fingers are too big and eyes too poor for that.

I put a new wire from the ignition switch to the coil when restoring the car a few years ago. Will double check that for continuity, etc.

This morning, as I was leaving for work, I pulled the wire from the coil to center of distributor and noticed a lot of rust inside the distributor. Would that cause an intermittent spark problem? Will replace the distr. as I have a new backup in the box.

Too busy to work on it for a few days. Will get back here after some more trouble shooting.

Yes!

Rust or corrosion in the distributor cap contacts can really reduce the spark as can water.

Sorry I meant to say I found rust inside the center post where the secondary coil wire to distributor is attached. The inside of the distributor is fine. But I think I have found the problem. I did a continuity check on the secondary wire and it must have a short as there is none. This is from an almost new set of wires I got from one of our main suppliers not too long ago.

Beginning to wonder about the quality of their products as two new point sets I also bought do not seem to work correctly as the engine ran rough with either of them installed. This was before the current issue. I put the old points back in and it ran fine until the current problem.

I will try to work on the car tomorrow and let you know what happens.

Most point sets have a preservative on the contacts. It is necessary to clean them when installed. In most cases a dollar bill swiped between the contacts a few times is all that is required.

Ok, I'm fairly certain I have the problem solved. Turns out the newer secondary coil to distributor wire had an intermittent short. Put the old one back in and it started up and ran. Also, when changing the points and/or condenser a couple times, I think I shorted the bolt that connects them together to the distributor housing.

I guess I have been away from these older ignition systems a long time. I don't recall ever cleaning new points. But with them installed again it did run a bit rough but smoothed out nicely after running for about 10 minutes. Maybe they are self-cleaning points;)

Thanks for your reply!