No spark on two cylinders

[BVZ24]

I'm wrapping up an engine swap. I had hoped I'd be ready to drive on the 4th, but could not get the two cylinders closest to the radiator to fire and spent most of the 3rd troubleshooting.
I ran a compression test and read a consistent 85 psi (police head) across all 4 cylinders.
The distributor was taken out of the previous engine that had run fairly well but had excessive main babbit wear.
The point's spring was very weak and replaced with new made points.
The condenser was also replaced with the points.
The coil was left alone and not changed.
The vehicle has a 12v conversion and the replacement condenser was ordered as 12v. I am not sure if the coil is a 6v or 12v coil.
The timing cam appears to be a newer B type cam, and although some wear was noticed, all lobes open the points within spec.
We retimed several times and it was rechecked by a local club member after the final time.

I have a clear cover and I noticed a bright blue spark off the rotor points on the firing cylinders, and nothing on the dead cylinders.
I tried various combinations of New reproduction, New old stock, New old stock reproduction, and take off distributor caps and rotors and the best I accomplished was getting the cylinder closest to the distributor to fire about 50% of the time with no change to the one close to the radiator.

Any ideas what I'm missing?
I'm currently thinking I need to try a new condenser and new coil. I found some information indicating that these can remain 6v parts and may order one of each in 12 and 6. I can find 12v coils locally.
How specialized are the 12v condensers? Can they be found at some of the bigger named auto parts stores?

Edit also ruled out spark plugs and copper clips by swapping the dead plugs to the working cylinders. Plugs removed from the dead cylinders would have gas on them.

[BRENT in 10-uh-C]

Sounds to me like the upper distributor plate is worn, -and/or the distributor housing is worn at the upper area where it pilots the upper plate. When that happens, the distributor points cam does not provide equal lift to all four spark plugs due to the plate being offset.

[nkaminar]

Did you try a new housing (the part that the straps connect to that lead to the plugs)? It does not sound like this is the problem but I thought I would ask.

Is the gap between the rotor and the points on the housing the same all the way around? If you have a marginal system a slightly larger gap may cause some plugs not to fire. You might try to close up the gap a little by bending the metal part of the rotor. The specification is 0.025 inch, I think, but I try to run a really close gap because my engine runs better that way.

Even though the cam seems OK, you may want to change it. It could be that a part of the cam is shorting out the moving point arm. This is a reach but look at it anyway. You can put a volt meter on the moving arm of the points and turn the engine over by hand to see if there is something shorting the points at the #1 and 2 plugs.

To test what Brent suggested, measure the point gap at each of the 4 locations.

[BVZ24]

I referred to the housing as the cap. I tried 4 housings. The best combination I had was a lightly used old reproduction housing with a new unbent rotor. I had no change with a bent rotor.

I don't know if it's worth noting, but this same housing always ran poorly before the rebuild. I did not have the New or NOS caps before the distributor was removed from the old engine.

[eagle]

I'd lift the spark plug straps an 1/8 inch or so from the spark plugs and look for a good hot spark jump. If the points are opening consistantly on each lobe as you crank the engine slowly, you should get spark. I've saw where people put oil in the cylinders and when trying to start the car the plugs fouled. Even excess gas or the use of starting fluid can short out plugs. Do the simple checks first, and looking for spark in this way is a very simple but important first check. If you can, put the car into a building or check in the evening so you can see the spark better.

[Gary WA]

Sponsored Links (Register now to hide all advertisements)

two bad plugs!!/?? seen it before!!

[rotorwrench]

The high tension cap assembly and rotor can easily be checked with a good visual for cracks or too much or too little gap between rotor & corresponding cap electrodes. A continuity check with an Ohm meter will show if they pass the high tension spark.

The current replacement points sets don't fit the original point block adjuster. A corrected point block adjuster is available to get best alignment. I'm still using old points that still align properly. If the OP is using the modern points then I can't say if they work well. I've never gone that route yet.

Modern condensers are suspect right out of the new package. I buy three to insure that I get at least one that works. The no blow model A type condensers work better than the modern pig tail types. There are no 6 or 12 volt condensers but there are 1.5 & 3.0 primary Ohm coils. The condenser capacitive reactance level depends on the coil design. A 1.5 Ohm coil will need a ballast on 12-volts but can run as is on 6-volts. A 3.0 Ohm coil will function with no ballast on 12-volts.

Points cams depend on who made them. Some are smooth & accurate while others are crap. Good advice already given on those.

[Gene F]

Where possible trade things around, and see if the problem moves.

[nkaminar]

The original poster has changed everything out except the coil. He does not know if the coil is 6 volt or 12 volt. Although a 6 volt coil should work on his 12 volt system, the next thing to do is to try a new 12 volt coil. One from the local parts store will work but the Model A coils are designed to work up side down whereas newer coils may not work in that position for long. The reason is that new coils may have oil in them to provide the cooling whereas the Model A coil has something solid, maybe a wax or resin. But a 12 volt coil from the auto parts store will work long enough to see if that is the problem. A volt meter should be used to make sure the new coil is hooked up correctly. If it has Batt and Ign marked on it, or something similar marked on it, the Batt side is negative. If the system is positive ground, the Batt side will go to the points and the Ign side will go to the battery.

Come to think of it, that may be something to check on the existing coil. A spark tester can be used to check the polarity of the coil, see https://www.snydersantiqueauto.com/p...6303&cat=41753

If the spark voltage is marginal, a slightly bigger gap or other small difference will keep the spark from occurring on all cylinders.

One other thing to try, if it has not been addressed, is to make sure the lead from the coil is all the way into the coil and the cap. Move the rubber covers back and push the wire home.

Also check the voltage at the coil to make sure there are no problems with the wiring or ignition switch or ammeter. If not 14 volts at a fast idle, there is some problem in the electrical system. That could make the ignition marginal and lead to the problem he is experiencing.

[BVZ24]

I'm not going to have the time today to test any of the suggestions but I will update once I do.
I would not have thought that the plate or housing could be worn out. It makes sense as it was always kind of picky on what upper housing it liked. I have a couple of distributors in various states of completeness and can swap lower housings and plates.

I believe the coil I can get in store is used with an external resistor. They say it's filled with high dielectric epoxy, which to me sounds like a non liquid cooling fill. It seems like a fairly easy swap to cover more bases.

[1crosscut]

Can you borrow a known good distributor from the local club member you mentioned in your first post and try it on your car?
Doing so would let you know if it was in your distributor or not.

[brokenspoke]

Vacuum leak on intake manifold??

[BRENT in 10-uh-C]

Geez, ....

[Phil Brown]

Originally Posted by BRENT in 10-uh-C

Geez, ....

[BVZ24]

Update
Replaced the lower housing and used the first housing's set of plates. I believe I had spark on 2-3 cylinders and it still sounded pretty rough. I forgot to turn the gas on and it ran out before I could watch the clear cover. I attempted to start it again by pressing the starter from the outside and could not get it to start again. I watched the clear cover and had no spark at any point in the rotor. I pulled the cover and checked spark at the points, and had no spark. I disconnected the existing coil, which has an external resistor, and connected my new coil, same results. I also switched the new condenser to the old one, and bypassed the key switch.
I next rebuilt the distributor with a new plate. I used a wireless conversion plate that eliminates the wire from the top to bottom plate. The upper plate converted is an older nu rex. I reassembled and repeated and did not get spark on the points before I ran out of time. Did not expect to go backwards.

[nkaminar]

Use your voltmeter to measure the voltage at the moving point with the points open or a piece of paper between them. If you have none, then back track until you find voltage. Unscrew the spring contact at the distributor and check there. That contact can be screwed in too far which will cause a short at the bottom plate. If no voltage at the spring contact keep back tracking. Check the voltage at the junction box. If voltage there then check to see if the ammeter is not open or some other problem between the junction box and the spring contact.

This is systematic detective work. You have to check everything in line from the battery to the points, including the battery connections and the ground strap.

If you don't have a voltmeter, go buy one. You can get a good one on line or at the local auto parts dealer, or Home Depot, for about $20.

Electrical circuits are very logical animals. The electricity flows in a loop. Any point in the loop that is open or shorted will cause the electrical system to fail.

The high tension part of the ignition system is a loop too. If the high tension wire is not inserted enough or if there are other issues with this circuit then you will have no spark.

Get the ignition system working first than chase down any poor performance which can be caused by a variety of things such as a bad condensor or the coil wired incorrectly.

This is a good reference for the Model A electrical system: https://www.mafca.com/downloads/Semi...ex%20Janke.pdf Bare in mind that the electrical system wiring could have been changed over the years. An example is a modern ignition switch installed and the wiring changed so that it supplies the power to the coil. But it is still only necessary to follow the current path to diagnose the problem.

[rotorwrench]

If your running a ballast resistor then check it with an Ohm meter. It should be around 1.3 to 1.5 Ohms but they do have a tendency to change as they heat up. You can also check the current to the coil as it's running. 3 or 4-amps is usually what a coil with a ballast will draw. If it's bad then the coil may never get the current it needs to function.

[eagle]

By simply replacing every possible suspect part you are probably introducing problems. Use the wiring diagram and a voltmeter to TROUBLESHOOT. #1. check both sides of coil, battery side should be battery voltage always, distributor side should be battery when points are open, 0v when points are closed (anything above zero, or very very close to it tells you there is a problem)- turn engine over slowly with the hand crank to verify this. #2. if dist side voltage does not go to 0v on point closure, then use your voltmeter on the points, then keep tracing back to ignition switch. Its a very simple system but throwing parts is never a good idea.

[BVZ24]

12v at ignition switch, 12v at ammeter, 12v at both terminals of the J-box. 12v at one side of the resistor and 6v on the other. Resistor is hot to the touch. 6v at the resistor side of the coil. Points open. 6v between coil terminals. 50mV frame to ignition side of coil. 50mv condenser side of points. 16mv other side of points to frame.

[BVZ24]

Either way I think I'm done for other reasons. Noticed a pool of slightly coolant flavored water on the middle head stud. There was a repaired crack on this stud and it appears that I have a head gasket leak.
I could not get the studs final torqued while hot because of the dead cylinders, but it's not looking good as I have not put the engine under any stress and it's still able to seep through.

[GPierce]

Originally Posted by BRENT in 10-uh-C

Geez, ....

I have seen this trouble shooting method too many times.

[Big hammer]

Originally Posted by BVZ24

12v at ignition switch, 12v at ammeter, 12v at both terminals of the J-box. 12v at one side of the resistor and 6v on the other. Resistor is hot to the touch. 6v at the resistor side of the coil. Points open. 6v between coil terminals. 50mV frame to ignition side of coil. 50mv condenser side of points. 16mv other side of points to frame.

Put the fancy dancy auto ranging vom back in your toolbox, go buy a 5 $ analog meter to use on your A.

[BVZ24]

Something in the range of 15 mv is near 0. It can be from small differences in temperature or alloy. When it switches from 15mv to 50mv I think fault or heat.

[BVZ24]

Solved.
The loss of two cylinders was a result of a worn out lower body. I assembled 3 distributor bodies on the bench and only one of them would spin in the center of the points. I thought it was funny that my good one was the one that cosmetically looked the worst.

The 2nd issue of no spark turned out to be a short in the top plate due to the insulator on the spring screw being under moulded and only covered half of the terminal. Replaced insulator with the insulator off of my old points.

[GPierce]

Solution was in post #2.

[Gary WA]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by BRENT in 10-uh-C

Sounds to me like the upper distributor plate is worn, -and/or the distributor housing is worn at the upper area where it pilots the upper plate. When that happens, the distributor points cam does not provide equal lift to all four spark plugs due to the plate being offset.

You won the dart game

[Patrick L.]

Thanks for posting the problem.