VCCA Home Forums TECHNICAL - GENERAL Electrical - 6 volt 1928 National AB Fordor Ignition

Guys,

Need some help from pros here. Distributor issues.
Changed points and rotor because of frequent misfire and erratic idle.
Now it won’t start at all LOL
I believe it has something to do with the points gap. I don’t think I need to redo TDC because I didn’t remove the shaft; only the points, gasket and rotor. I also believe I may have messed up the firing order. I have the original reprint of owners manual and the shop guide. But I don’t think the picture of the distributor on the wiring page matches what I had when the car was running well. Please help confirm the positions of plug cables on the distributor cap. I think the correct order is 1243. But where is plug number 1?

Thenks

All Chevrolets have No. 1 plug on the front toward the radiator.

While I doubt if your problem is a slight timing adjustment, you will need to reset timing when you get the engine running. The rubbing block on the new points will open them at a different position on the distributor cam.

Are you sure that the points actually open and close as you crank the engine? Have you verified that with a test light or an ohm meter?

I know this is basic but many of us have messed up setting the gap when the rubbing block was not on the peak of the distributor cam. So the points either never close or do not stay closed long enough for the coil to saturate and create a spark.

To add info to this discussion, here's a link to a write up I did about timing and starting procedures that I use: https://vccachat.org/ubbthreads.php/topics/450864/re-1928-1-ton-lp-truck.html#Post450864

Hope this helps. Dean

We just reset the gap by using a feeler gage around 0.020 thick. Yes they do open and close while cranking the motor. But I still have no spark. I do get 6v coming to condenser , side point and coil. But I’m looking into replacing the coil just in case

I’m also trying to understand how the timing adjustment screw at the bottom of the distributor operates that is connected to the manual spark control on the steering wheel

I think we did the TDC correctly, although I didn’t expect to do it in the first place, since I only replaced the points and rotor rather than remove the entire distributor shaft. So, we followed common steps like plugging with a thumb the hole number 1 for the compression stroke and then fine tuning the gap by hand turning the engine until the camshaft lobe center meets the point block. Still no spark tho.

The reason I started messing with the distributor in the first place was because, out of a sudden , I started getting crazy misfire on 2 or even three cylinders. Would not stall but would smoke black and dump gallons of gas into crankcase, while the intake manifold would get icy cold. All sparks would foul quickly but the engine started right away after good cleaning . And so on again. I think the vacuum canister and the carburettor were fine

I'm scratching my head thinking about "dumping gallons of gas into crankcase". It is an updraft carburetor so a sticking float would not flood the engine.

My best guess is that a check valve or the diaphragm in the vacuum fuel pump has failed.

With respect to the points and ignition, what voltage do you read at the coil/condenser when the point are closed? It should be 0 volts.

Thanks for your advise.

Well, in regards to the vacuum canister, although it’s old and the float had been resoldered hundreds of times; besides all of that, I would still have a pursuasive crankcase dilution even with the petcock that controls the flow of fuel at the bottom of the canister into the carb - remained crack open. So I strongly believe that the reason I was getting so much fuel into the pan is because of all the fuel pushed thru the rings without spark

I will remeasure the voltage because I don’t remember the position if the points since my goal was to ensure I don’t have any breaks in the wiring continuity delivering power to coil

Hey Dean, I am a little bit confused about the direction of the distributor rotor. According to the manual, looking from the top - its counter clockwise. Please advise. I can upload a photo from the book, if necessary

Should be clockwise, with the # 1 wire position generally toward the radiator.

Is the polarity of the coil primary connections relevant? I heard different opinions. And if yes, could the reversed hookup mess up the coil condenser? Thanx

Hi Bill

On the first question...
Yes, the polarity of the coil primary is generally considered to be relevant.
It's been said that it affects the way the electrodes erode on the spark plugs.

That said, I don't really know how much difference it will make as I've never run one reversed.
Maybe someone else has experience with that?
And... Chevrolet actually used a polarity reverser from about 1941 to 1948 which changed the polarity every time the starter was used.

To answer your second question...
No, condensers don't care about polarity and won't be affected by it.

Ole has some good “points” to consider. Could not resist the pun!

He is correct that the function of the coil is not polarity sensitive. It is a transformer that will create the same induced output current regardless of polarity. However polarity of that output current is sensitive to the polarity of the input current.

He is also correct that the polarity will affect the direction that the spark jumps at the spark plugs. Based on what I understand it takes less energy to make the spark jump from the center electrode to the end or side electrode. That is due to the temperature difference of the 2 electrodes. The center one is smaller and runs hotter. The “ground” electrode never gets as hot because it is connected to a whole lot more mass. Making the spark jump from cold to hot takes more energy.

That is why I never completely understood the reason that Chevy installed a polarity reversing switch. It was supposed to make the ignition points last longer but it could mean spark issues at the plugs.

Thank you very much for the information. I still have a lot to learn. Luckily there is no polarity switches in 1928. I’m still struggling with the no spark issue after points replacement. So I was wondering if that might have been the reason that the power wire was hooked up to the negative terminal on the coil; while the positive terminal lead to the distributor and the condenser. I don’t remember switching the polarity when the car was still running.

I have found that new points that have been stored for a while can get an insulating layer on them. Too many times I have had to clean the points to get them to work well. Just a little abrasive, even a crisp dollar bill can do it.

That is exactly why I asked what voltage readings you are getting with the points closed compared to open.

More than once I have found that either the points did not conduct electricity when they were closed or that the moving arm of the points was grounded. In the latter case the current to the coil is not interrupted when the points open.

I see. But nonetheless, is the negative terminal on the coil ground itself on the distributor casing? Or polarity doesn’t matter?

I imagine it might work either direction, but I just want to know how it’s supposed to be by the book

Under normal circumstances the + terminal is connected to the ignition switch and the - terminal connects to the insulated screw on the side of the distributor which should connect to the moving point (also insulated from the housing) and condensor which mounts to the distributor housing. The fixed point is mounted to the distributor housing (ground). When you turn the key on with the points open connect a light globe (test light) between moving point and ground the globe should light up, close the points and the light should go out, this is the time there should be spark out of the coil (with a 1/4" gap between the coil output (3rd terminal) and ground.
Tony

Can you please also explain me a little bit about the screw with a spring at the bottom of the distributor which is also connected to the spark lever. Greatly appreciate that

The spring that you're talking about is a shoulder bolt holds the distributor down to the block, but it also allows the distributor to turn for advancing or retarding the spark. The full turning movement of the distributor equals roughly 25 degrees of rotation.

I put a drop of motor oil on that spring once in a blue moon so it can slide across the mounting plate easily.

Cheers, Dean

Thanks for the information. That’s what I thought. But how loose or tight does it need to be at if needs to be tight, in which position of the distributor do you tighten it. It seems when tighten it, the distributor won’t move at all. How loose should it be?

Since the bolt has a shoulder that goes through the distributor clamp plate, the bolt needs to be tightened into the hole in the block.

The head of the bolt will stick above the clamp plate with enough room for the spring. The spring pushes against the top of the clamp plate and the underside of the bolt head, thus keeping the clamp plate under tension with respect to the block, but able to slide on the block to provide the retard and advance settings of the distributor.

The shoulder bolt is the only thing that keeps the distributor in the correct position (up and down) in the distributor hole in the block.

Clear as mud, right?

By the way, make sure to tighten the clamp bolt really well where it clamps around the distributor. I've experienced the distributor 'walking' up out of the distributor hole in the block because clamp bolt was not tight enough. The result was that the gear at the bottom of the distributor driving shaft lifted up enough to disengage from the oil pump, causing a total drop in oil pressure. Not good.

Loosening the clamp bolt and slowly hand turning the engine until the distributor dropped back into the slot of the oil pump shaft and then re-tightening the clamp bolt solved the problem.

Dean