M43 Ambulance - Distributor Questions

[toddbe]

I have converted the engine back to 24 volts. I change the oil pump and distributor. There is a new coil installed, new points and new condenser.

As I turn the engine over by hand there is power on the right-hand side of the points when the points are separated. There is no power (electricity) to either side of the points when they come together. this appears to be completely opposite, it would seem there should be powered when the points come together.

Obviously the engine is not starting, but I'm wondering if this is the problem. If it is, how do I correct this. I made a video to upload however does not appear I can upload a video to show the problem.

Any help would be greatly appreciated. Todd


Added info, maybe helpful - wiring to coil, positive side of coil is power from ignition. negative side of the coil goes to point/condenser. The power to the coil matches within the distributor points are open, then power disappears when points are in contact.

 

[NDT]

What you are describing is as it should be. When the points are closed, the negative side of the coil is connected to ground. Do this: remove all 6 spark plugs, reconnect them to the waterproof wires. Crank the engine and place your finger over the spark plug hole. Verify there is a spark at the corresponding spark plug when your finger is popped off the hole by compression.

 

[toddbe]

NDT - thanks for educating me. More testing -

Power to right side of points as stated above.
No power to rotor
No power to distributor shaft.

I will be pulling the plate out to look for the issues. Any advise?

Todd

 

[NDT]

Plate? As in the plate that the points mount to? Why? The terminal that the yellow wire goes to will be energized with the points open and deenergized with them closed. I see a chinese chrome coil, those suck.

 

[toddbe]

NDT, As the photo show and as stated, there is no power to the rotor even though there is power to the points. Obviously as there is no power to the rotor there is no power to the spark plug and likely the reason (or at least one reason) for not starting.

So I guess my question is, Where should I be looking for the 'disconnect' of power?

 

[NDT]

The rotor does not have voltage going through it until the dist cap is put back on.

 

[toddbe]

The rotor does not have voltage going through it until the dist cap is put back on.

I have attempted that and tested it. After the distributor cap is on I have tested for power through the spark plug wire. Nothing. Then I removed the wiring from the distributor cap and tested for power on the rotor while in position for power to the plug, again nothing. There is power to the neg side of voltage at this time. So I'm still searching for the 'disconnect'.

 

[NDT]

Just to be sure, you are aware that the spark plug voltage is like 15,000 volts, correct?

 

[pjwest03]

I have attempted that and tested it. After the distributor cap is on I have tested for power through the spark plug wire. Nothing. Then I removed the wiring from the distributor cap and tested for power on the rotor while in position for power to the plug, again nothing. There is power to the neg side of voltage at this time. So I'm still searching for the 'disconnect'.

You will not get power through the spark plug wire in a static state. The coil only generates voltage when the magnetic field in the coil collapses when the points open. The coil voltage will 15,000+ at that point and kill your meter. The only way to check the spark is first to have the system assembled. Then take one plug wire and one plug, make sure the body of the plug is grounded, and then crank the engine. If things are good, there will be a blue spark. They make specific spark gap testers but a plug will do fine.

The coil is a transformer. Only a fluctuating magnetic field will induce a voltage in the high voltage side. When the points close the primary winding of the coil is energized and creates a magnetic field. Then when the points open, the magnetic field collapses and induces a voltage in the secondary winding. The secondary winding has many, many more turns of wire than the primary so... The secondary winding will have a much, much higher voltage. In modern engines that can be 60,000+ volts.

A quick video that is representative: https://www.youtube.com/watch?v=mUOmsGiirTU

 

[toddbe]

pjwest03 - thank you very much for the education. I've tried to check the spark before in this manner, but not since fixing some wires. I will check this tomorrow am.

 

[toddbe]

Just to be sure, you are aware that the spark plug voltage is like 15,000 volts, correct?

NDT - yes, but thanks for the reminder. However it is the amp that kills not the voltage :}

 

[toddbe]

pjwest03 - I tried the information that you suggested. I checked with 3 separate spark plugs / spark plug cable. No joy, there is no spark from any of the.

Anybody have suggestion on how to continue the search for the problem??

 

[pjwest03]

At this point, I would try another ignition coil.

 

[toddbe]

The problem - no electrical continuity through the distributor cap. Ugh. Replaced and I now have spark. Still not running so I tested the compression. Darn it all are in the 30's-40's. It is wonderful that we have great manuals.

 

[M543A2]

Take a length of #12 or #14 electrical wire, fasten one end to a ground on the engine, with the distributor cap removed, place the other end in the top center of the coil so it is a short distance, about 3/16 inch, from the silver button down in the center of the coil so a spark can jump to it from the button and be seen. You can bend the bare wire end 90 degrees so the bent end will hang in the coil center insulation pocket, the end of the wire 3/16 inch from the button. This will help keep it from falling out of the coil as you work. With the motor turned so the points are closed, ignition on, use a non-conducting tool to by touching only the points moveable arm, pull it away from the non-moving contact. You can do this with a metallic tool as long as you do not ground the point moveable arm to anything else or the test will be no good. Whenever you let the points make contact then pull them open you should see a spark at the button in the center of the coil to your grounded wire. If no spark, turn the motor so the points are open and with a metal tool like a screwdriver tip, make contact from the points moveable arm to the non-moving point frame. If you get a spark from the coil when doing this, then the points are bad.

 

[tankdriver]

They sell a tester that has a light in it, that lights up when the plug fires. You unplug any spark wire in plug it in. That will test everything in the system real quick. If it lights up, everything is OK. I'm a mechanic, and use it quite often. Well worth the money for the time it saves. It will work on any spark engine.

Are you sure you put the distributor in correctly, and not 180 out?

 

[mdainsd]

"compression in the 30s and 40s", no amount of spark is going to get that engine running.

 

[tobyS]

"compression in the 30s and 40s", no amount of spark is going to get that engine running.

Probably valves or valves and rings. They make an electronic ignition for changing almost any points over that eliminates the points problem.