Carbon tracking through rotor. More HEI woes.

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iScamp

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Need some help with a failed ignition system. I did a Forum search and found one result that might be helpful, I'll get to that in a bit.

Here's the setup:
'72 340 Mopar. Has been converted to use a GM HEI module. Blaster II coil recently replaced as part of troubleshooting. Symptoms occurred with either old or new coil.
New Taylor plug wires, 8.5mm. New spark plugs, NGK, gapped .040". (sorry can't find the part number right now, if it's important to troubleshooting I'll go out and look)

The ignition system has failed twice now. Both times a bad distributor rotor. The car runs great and after 200 miles or so, starts 'missing' and running rough. Changed the rotor and it runs great again. Decided the HEI was burning through the stock chinese rotor. Bought a tan Accel cap and rotor designed for HEI ignition systems. Again,after ~200 miles cumulative driving the engine started running rough (this weekend). Put an old, known good rotor in it (temporarily) and it runs great.

Looks like the high tension voltage is going from the rotor tab directly to distributor shaft.

Someone from a post back in 2014 here on FABO said, 'if it has resistor wires and resistor plugs, they won't do well together' or something similar. I've got both on this car.

Why would the spark go through the rotor? No moisture ever noticed in the cap. it is a vented cap.
 
What brand and number rotor are you buying? It's harder than ever to get hold of good quality caps and rotors any more. You should be able to get hold of a rotor that will hold up over a reasonably long lifespan for you. Double-check the centre carbon contact in your cap, too; if that is burned up or faulty, it can destroy the rotor.

Grab a cup of coffee and read through this (entire, long) thread. Proceed as recommended and I bet you won't have to think about your rotor for quite awhile, and other stuff will probably get better, too. Only departure from \6 practice as described in linked thread is that you might wind up wanting a somewhat narrower business end of the rotor to account for the shorter spacing between adjacent cap terminals on a V8 application. Try it as directed and see how it works; you can always take a Dremel to the brass and narrow it a bit if that turns out to be needed.
 
What brand and number rotor are you buying? It's harder than ever to get hold of good quality caps and rotors any more. You should be able to get hold of a rotor that will hold up over a reasonably long lifespan for you. Double-check the centre carbon contact in your cap, too; if that is burned up or faulty, it can destroy the rotor.

Grab a cup of coffee and read through this (entire, long) thread. Proceed as recommended and I bet you won't have to think about your rotor for quite awhile, and other stuff will probably get better, too. Only departure from \6 practice as described in linked thread is that you might wind up wanting a somewhat narrower business end of the rotor to account for the shorter spacing between adjacent cap terminals on a V8 application. Try it as directed and see how it works; you can always take a Dremel to the brass and narrow it a bit if that turns out to be needed.

I'll take some time and definitely read the link you posted.

The cap and rotor were originally whatever came from the local parts house.
That rotor (white) failed by carbon tracking.
Bought new Accel tan cap and rotor. I've got the paperwork stashed somewhere. but, it was advertised to withstand 60k volts for so. Carbon tracked through that new Accel rotor. Put in an old rotor from another car and the 340 runs fine. Same cap. I'm sure it will burn through the flimsy OEM rotor soon. New cap looks great inside.
 
"Electronic Pickup Polarity and Rotor Phase", use the search bar function, pick-up coil and stator may not be aligned with rotor and cap tower contacts......
 
The rotor burn through was a problem right from the rip with the GM HEI. The spark is so hot it's GONNA find ground somewhere eventually. When I ran Chevy stuff, I always carried a spare rotor. The Standard Blue Streak line lasted longest and is still available today for the Mopar application.
 
^^This is true but the more gap or resistance in the secondary circuit, the higher the coil voltage climbs. Similar to lightning, looks for an easy place to go.

1....CAREFULLY inspect EVERY part of the secondary (high voltage system) to look for high resistance or spark gaps. This includes poor plug wires and or coil wire. It also includes plug types with "trick" gaps or even a bad plug. It HAPPENS

2...Rotor phasing. If the rotor does not track the tower contacts when the spark fires, there will be a big gap between the rotor contact and the associated tower contact, and it will look for "somewhere to go."

Lacking that I'd look for better quality rotor and "if you can't find" then investigate say, some thin teflon or other high voltage insulation in thin sheet form that you can lay on top of the dist. shaft under the rotor

High voltage gaps TAKE OUT HEI and other modules. For example, NEVER allow an electronic system to fire, either cranking or running, purposely, with a plug disconnected. The high voltage pulse on that open circuit will backfeed or reflect a pulse back into the electronics
 
^^This is true but the more gap or resistance in the secondary circuit, the higher the coil voltage climbs. Similar to lightning, looks for an easy place to go.

1....CAREFULLY inspect EVERY part of the secondary (high voltage system) to look for high resistance or spark gaps. This includes poor plug wires and or coil wire. It also includes plug types with "trick" gaps or even a bad plug. It HAPPENS

2...Rotor phasing. If the rotor does not track the tower contacts when the spark fires, there will be a big gap between the rotor contact and the associated tower contact, and it will look for "somewhere to go."

Lacking that I'd look for better quality rotor and "if you can't find" then investigate say, some thin teflon or other high voltage insulation in thin sheet form that you can lay on top of the dist. shaft under the rotor

High voltage gaps TAKE OUT HEI and other modules. For example, NEVER allow an electronic system to fire, either cranking or running, purposely, with a plug disconnected. The high voltage pulse on that open circuit will backfeed or reflect a pulse back into the electronics

I remember some Buicks and Cadillacs in the mid to late 70s had plug gaps at .120"! I always thought that was excessive......but they ran good.
 
Need some help with a failed ignition system. I did a Forum search and found one result that might be helpful, I'll get to that in a bit.

Here's the setup:
'72 340 Mopar. Has been converted to use a GM HEI module. Blaster II coil recently replaced as part of troubleshooting. Symptoms occurred with either old or new coil.
New Taylor plug wires, 8.5mm. New spark plugs, NGK, gapped .040". (sorry can't find the part number right now, if it's important to troubleshooting I'll go out and look)

The ignition system has failed twice now. Both times a bad distributor rotor. The car runs great and after 200 miles or so, starts 'missing' and running rough. Changed the rotor and it runs great again. Decided the HEI was burning through the stock chinese rotor. Bought a tan Accel cap and rotor designed for HEI ignition systems. Again,after ~200 miles cumulative driving the engine started running rough (this weekend). Put an old, known good rotor in it (temporarily) and it runs great.

Looks like the high tension voltage is going from the rotor tab directly to distributor shaft.

Someone from a post back in 2014 here on FABO said, 'if it has resistor wires and resistor plugs, they won't do well together' or something similar. I've got both on this car.

Why would the spark go through the rotor? No moisture ever noticed in the cap. it is a vented cap.

You also might try the Napa MO3000 rotor.
It's .030 longer on the tip putting it much closer to the cap terminals.
Been running the same one for years now with HEI.
I have also seen lots of GM rotors burned down through the center.

You do have to be very careful to make sure the cap is on straight with this rotor.
 
I remember some Buicks and Cadillacs in the mid to late 70s had plug gaps at .120"! I always thought that was excessive......but they ran good.

Not so, but close GM had a .060 plug gap for a long time but after B
P said they would pay for any toes caused by fuel line freeze up
and GM had a lot of no starts in cold weather that changed things to .045 gap and the cold start problem went away.
 
Not so, but close GM had a .060 plug gap for a long time but after B
P said they would pay for any toes caused by fuel line freeze up
and GM had a lot of no starts in cold weather that changed things to .045 gap and the cold start problem went away.

Yes sir. GM used .060, then .080 and finally .120. I was there, on the line working live and in person everyday. They were trying to experiment with emissions control.
 
Does the cap have brass terminals or the silver terminals? Too much gap to the cap Center terminal is causing ur problem. Kim
 
Is the spark going through the plastic to the dist shaft, or along the outside.

Tru HEI rotors have a lot of material between the dist shaft, and the contacts.

You could try an experiment, and cut a disc out of a plastic milk carton (or the like) and put it under a new rotor in such a way it won't interfere or come loose and see if doesn't help or cure the problem
 
Many good comments, there are electrical measurements that can help.
1. Ohm out plugs, cables and cap from plug tip to cap inner terminal. Typically a few 1000 Ohms, it varies with length. One open cable can create your problem.
2. Use a scope with high voltage probe (2Kv) to monitor coil plus. The secondary voltage is approximately coil turns ratio times peak coil primary voltage. Typical peaks 300 to 500V. So with 100 ratio, 40kV at 400V. Use time base to look at one in detail, 8 for consistency. When high peak strikes over plug, voltage goes low, and the decays, those should look similar too. Plug wires are part of voltage drop too.
3. Monitor coil current with scope by inserting 0.1 Ohm 10W NH (non inductive) in series with coil, use scope on resistor terminals, using suitable isolated input scope or 2 channels in differential mode. Wave form will show coil charge time (varies by tyipical a few ms) and peak current. The current measured is 10x voltage, so 0.5V peak is 5A.
Typical peak currents reach 3-5A for Mopar electronic, but up to 7A for GM HEI One solution is to add ballast resistor as necessary to bring current down. That will also bring down secondary voltage. With a well tuned engine 20kV, is often enough. To much or too little fuel is not best fixed with ignition.
 
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You can make your own extended tip. Ace Hardware sells small pieces of brass stock. Throw the rivet away and use a small sheet metal screw with a drop of epoxy. you also want to make sure the rotor fits snug as you push it on the shaft, (no slop).
To phase the rotor remove the roll pin and throw it away. Drill and tap the reluctor 180* apart and use 2 6-32 set screws to adjust the reluctor and phase the rotor. The cylinder fires as the reluctor rotates past the pickup.
 
Typical GM engineering. The get the design most of the way done, don’t thoroughly test it, & let the public work out the rest of it.....
 
Need some help with a failed ignition system. I did a Forum search and found one result that might be helpful, I'll get to that in a bit.

Here's the setup:
'72 340 Mopar. Has been converted to use a GM HEI module. Blaster II coil recently replaced as part of troubleshooting. Symptoms occurred with either old or new coil.
New Taylor plug wires, 8.5mm. New spark plugs, NGK, gapped .040". (sorry can't find the part number right now, if it's important to troubleshooting I'll go out and look)

The ignition system has failed twice now. Both times a bad distributor rotor. The car runs great and after 200 miles or so, starts 'missing' and running rough. Changed the rotor and it runs great again. Decided the HEI was burning through the stock chinese rotor. Bought a tan Accel cap and rotor designed for HEI ignition systems. Again,after ~200 miles cumulative driving the engine started running rough (this weekend). Put an old, known good rotor in it (temporarily) and it runs great.

Looks like the high tension voltage is going from the rotor tab directly to distributor shaft.

Someone from a post back in 2014 here on FABO said, 'if it has resistor wires and resistor plugs, they won't do well together' or something similar. I've got both on this car.

Why would the spark go through the rotor? No moisture ever noticed in the cap. it is a vented cap.

I had an issue with my MSD Pro-billet doing the same thing. It actually melted the tip off the MSD rotor, blackened the rotor between the center contact and the tip and really burned up all the plug terminals inside the cap.

Through research and advice here, I found that my phasing was very far off, and suspect that your phasing is off too. When it is, the spark has to jump a longer distance from the rotor tip to the respective ignition wire terminal inside the distributor. That creates a lot more heat than it normally generates.

Take an older cap, drill a 3/4" or so hole between the center terminal and the #1 plug tower and flash your timing light in there. You'll need to either use an adjustable rotor or adjust your reluctor or trigger wheel to alter the phasing.

Once I did that, the rotor and cap terminals began to look normal again.
 
Typical GM engineering. The get the design most of the way done, don’t thoroughly test it, & let the public work out the rest of it.....

When I worked for Cadillac That is exactly how It was, after we figured out that the manual was wrong fixed that then fixed the car GM did say thanks though,
 
A bit more on rotor phasing. As jbc426 says the reluctor and rotor are fixed together, as timing advance changes phasing stays the same relative to pickup sensor. If sensor changes position, with vacuum advance, the phasing changes. If cap is indexed differently that changes phase. Mopar distributors typically index the cap, on a tab that is part of vacuum advance. If your distributor has vacuum advance, check out how that might influence phasing, and what indexes cap.
 
Thanks for all the inputs.
oldkimmer: brass contacts in the cap
Dana67Dart: Going through the center of the rotor.
kitcarlson: Getting an O scope is not practical at the moment. Interesting data. I used the Sun machines, way back. Very useful tool. I will consider a ballast resistor. but that was one of the selling points of having the HEI, no ballast.
Other suggestors:
will definitely look at rotor phasing. And modifying the rotor.

Plugs, wires, cap and rotor are all new. I know that doesn't mean much these days. But all are designed, uh well, marketed as for HEI systems.
 
You could always ditch the HEI and go back to a Chrysler performance system. We know you won't have problems with that! :poke::rolleyes:
 
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