1950 Chevy 3100 No Spark

[ewhitaker0020]

Hello, I'm trying to help my father-in-law get his truck running again. It has sat for about a year and now we can't get it to start.

The engine turns over fine, the battery is fully charged and as far as we can tell it's getting fuel. The problem is that it isn't getting any spark to any of the spark plugs. I took a wire off one of the spark plugs and stuck it to the engine block while he cranked the engine and there was no spark at all. I did this to all of the spark plug wires and got the same result.

So we assumed the coil was bad and got a replacement. A big thing to know about this truck is that it originally had a 6 volt generator system, but now has a 12 volt alternator on it and has ran just fine for the last 3 years. No problems getting spark or anything. The coil that was on the truck is a generic 12v tractor coil, but has worked just fine. The replacement that I got has a part number 2-5195 and looks exactly like the old one except it has writing on it. Something about adding a resistor. I have no idea what it wants me to do since the old one worked just fine.

Something else that I'm confused about is the instructions I found online (very vague instructions that I think are for this part) and the instructions in the truck manual make it sound like the positive wire from the ignition switch goes to the positive lead on the coil. Then the negative lead on the coil goes to the distributor. The problem is... this is backward to how the last one was hooked up. I took pictures just to make sure and these instructions tell me to hook up the new coil backwards compared to how the last one was hooked up. The old coil worked just fine.

The replacement coil didn't produce any spark either. Just to make sure it was getting voltage I checked both sides of the coil to the engine block and it read over 12 volts on both leads. Then I had unplugged the main spark plug wire that goes from the coil to the center of the distributor from the distributor and held it to the engine block to check for spark while he cranked the engine and there was no spark.

What are we doing wrong? I have no idea what to do next. We cleaned the rotor button and the points, but I don't think it matters because there's no spark getting to the distributor as far as I can tell.

Here's a link to some pictures of the whole set-up with some descriptions on each picture.

https://imgur.com/a/ffq79ST

[GreasyLikeaBurger]

Have you checked to see if the distributor is turning with the engine? Maybe the gear is not meshing properly with the cam or the pin broke that holds it. Quick to check.

[ewhitaker0020]

Originally Posted by GreasyLikeaBurger

Have you checked to see if the distributor is turning with the engine? Maybe the gear is not meshing properly with the cam or the pin broke that holds it. Quick to check.

Even if the distributor isn't turning, shouldn't I have gotten a spark from the main wire coming from the coil?

[dsraven]

ok, I have to assume the battery has a good ground on the engine if it is cranking fine. there is fuel and the spark plugs are visually wet when checked after cranking. no spark condition is verified by leaving a small gap between the plug wire and a good ground or using a spark plug on the end of the wire and grounding the threaded part of the plug against a good ground. so no spark is the problem. you need fuel, heat (compression) and spark.
-have you looked at the condition of the points? run a white business card through them to see if it come out black from junk collected on the points? checked the gap? spray with electrical cleaner and retry? replaced the condensor? was it running well when parked, possibly just dirty points? no work done on the truck with the key left on for extended periods that would fry the points/condensor? checked the distributor rotor and cap for corrosion even under the plug wires and in the towers of the cap? rotor turns when engine is cranked?
-check the voltage at the pos connection to the coil. disconnect from the coil and check. should be the same as battery voltage with the key in the start position and less than that, like 9 volts, in the run position. this is because coils burn out quick if they get 12v all the time. there is usually a ballast resistor inline with the "run" position to cut the voltage down. and another wire from the starter to supply a full battery voltage to the coil while starter is engaged. if you don't have a resistor then the coil could simply be burnt out. google how to check an ignition coil
http://www.autos.com/car-maintenance...-ignition-coil
-check the connection to the distributor because the insulator through the housing can short out. key off, you can disconnect the (-) wire at the coil and use an ohm meter with one lead on that wire and the other lead on the engine block. open the points by hand, or a non conductive tool, and see if, when the points are open the circuit has high resistance. if it acts like the points are closed then there is a short to ground somewhere in that circuit and the insulator block would be the first place to look or next would be the flat spring on the points or the insulated wire connection at the points shorting on the backing plate. it could also be the condensor shorting internally. long story short- when the points open there should be no grounding of that coil wire. when they close the wire should ground with very little resistance as if the ohm meter leads were touching each other. if not then find out why.
-if the ground thing is fine then check the condition and gap of the points. check the rubbing block for excessive wear and also the cam on the distributor shaft. some lubricant here is required but too much may have been put on at some point and could be gumming up the points causing poor conductivity through their contacts when closed. when the points open the current should that is "backwards induced" in the coil windings should not be allowed to jump the gap on the contacts, that is the purpose of the condensor. it stores the voltage so it won't jump. then when the points close the condensor gives up that voltage, whick also assists the coil to fully charge the primary windings. a bad condensor will cause burnt points. here are a few sites to read through basic operation.

https://www.youtube.com/watch?v=LT4m2LLKwnE

https://www.youtube.com/watch?v=LT4m2LLKwnE

https://www.youtube.com/watch?v=PCs5gAZBbxU

https://www.youtube.com/watch?v=W94iksaQwUo

http://classicmechanic.blogspot.ca/2.../ignition.html


hope this helps get'er going.

[ewhitaker0020]

Thank you for all the info. I don't understand everything you said, but most of it. I will show this to my father in law and we'll go through all the things you mentioned.

[dsraven]

also, you should have a nice blue spark, sometimes hard to see if it's full sunshine. you should hear it snap though.
-check points for dirty contacts and proper gap
-check for short to ground in distributor
-check ballast resistor, so power to coil (+) when cranking and also when not cranking but key on. take (+) wire off at coil for this because the rest of circuit can mislead you, like if the points are closed or there is a short in the distributor
-check coil

the other thing I just thought of is checking the coil power with the wire off but a load, like a light or a fan motor, put on the wire. if the light/fan works no problem then it its fine but a volt meter can show voltage under no load. a bad connection at the ign switch or a fuse can fool a volt meter.