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Distributor cap/ rotor

Discussion in 'Repairs, Maintenance, Help' started by Hidden1, Dec 20, 2017.

  1. Hidden1

    Hidden1 New Member

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    I have a 02 dakota 3.9 an noticed dark marks across the points on inside of distrutor cap along with burn like marks on rotor button.
    What causes this an what symptoms do you get from it ?
     

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  2. valiant67

    valiant67 Rich Corinthian Leather
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    Perhaps someone can explain it better, but the burn marks are caused as the spark jumps between the surfaces. Better caps and rotors have copper contacts which last longer and don’t “burn” as quickly.

    Replace the cap and rotor with new. If any doubt replace plugs and wires too.

    You may get a misfire or weaker spark from the contaminated surfaces. Or it may not be noticeable at all.
     
  3. Hidden1

    Hidden1 New Member

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    I was having a slight miss that came an went at times an once in a while a pop .
    Cylinder misfire code..
    Seems ok since replacing plug wires an plugs then cap rotor..
    I am trying to avoid it from happening an didn't expect burn mark on rotor.
     
  4. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    That's normal wear from arcing. How many miles on those? I change mine every 30K miles.
     
  5. David Eidell

    David Eidell Well-Known Member

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    Does any manufacturer make those "high alkyd" caps and rotors anymore? Those blue or brown ones. I had good luck years ago with them. NAPA stores had them. They definitely reduced carbon tracking.
     
  6. 68RT

    68RT Well-Known Member

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    If you can find brass on the cap, you have a better quality. Aluminum fails quicker but does last a fair amount of time.
     
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  7. ImperialCrown

    Level III Supporter

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    Minor terminal burning is normal and may not cause any drivability concerns. Corrosion may mean the presence of water/humidity in the distributor which can cause problems.
    The center carbon button should have a shiny spot where it touches the rotor contact. If the button is dull, it isn't touching and any arcing will burn here.
    I like the brass contact ignition terminals as they seemed to hold up better.
    In high school auto shop, we had a V8 with a clear distributor cap. With the engine running, it looked like a circular lightning storm inside the distributor.
    I have seen aftermarket 'mismatched' caps and rotors where the rotor didn't meet up correctly with the cap. Use the same brand for both. OEM parts are preferred.
     
  8. David Eidell

    David Eidell Well-Known Member

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    Back when dinosaurs roamed, I discovered to my horror that distributor rotor quality was not uniform on MoPars. A rotor could be slipped onto the shaft and then seated. But twisting the rotor produced a click-click. Loose on the shaft. Talk about variable ignition timing! And badly worn distributor shaft bushings -- Today's cars are so much better.

    Those brown and blue high alkyd caps and rotors I mentioned have brass terminals. But it was the carbon tracking from cylinder to cylinder or from center contact to one of the cylinders that bugged me. Back then 25 cent carwash stalls were the rage. So what Imperial Crown, noted is most certainly agreed with. And those were the days of narrow spark plug gaps in the .032" range. Aftermarket distributor caps for FoMoCo were awful -- the little notch in the cap did not agree with the tab on the lip of the distributor body.

    I shudder when I look at gasoline prices and malfunctioning ignition parts.
     
  9. dana44

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    I can agree. Caps and rotors do wear out, 30K is kind of pushing it for wear limits, used to change them every 12K miles in the past, plug wires, unless wire instead of the carbon cores last every other spark plug changing because the resistance connection breaks down when disconnected, the wire plug wires last longer as long as they don't become corroded. If the mileage isn't reached, about every two years is then a good timeframe to change cap, rotor, plugs, and wires every other plug change.
     
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  10. 68RT

    68RT Well-Known Member

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    You will find that the corrosion build up can be knocked off with a knife if cap needs to last a little longer. It is more of oxidation than corrosion.
     
  11. dana44

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    And at the same time, the oxidation needs to be cleaned really good inside to alleviate the chance of the electrical spark from tracking along the oxidation and continue the arcing and misfires.
     
  12. KOG

    KOG KOG
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    Loose rotor doesn't affect timing. But it can sure cause other trouble. Loose bushings will scatter timing all over the place as well as varying dwell to the point of no fire at times.
     
  13. ka9yhd

    ka9yhd Active Member

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    Years ago they used to make distributor caps with internal ribs to minimize the carbon tracking on the inside of the distributor caps. But now all I can find are one that are smooth on the inside without any ribs.
     
  14. dana44

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    Yeah, I kind of like the smooth ones so you can clean them out easier. As long as the contact points for each plug wire is not grossly destroyed, scrape the contacts clean and see how that makes her run, or replace.
     
  15. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    He described lateral rotational play, which I've never seen; but if true, it could affect timing.
     
  16. KOG

    KOG KOG
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    If the shaft is loose, yes. If the shaft is tight and the rotor is rotating on the shaft it has no effect on timing. Timing is a function of the shaft operating the points.
     
  17. Rickorino

    Rickorino Well-Known Member

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    Even the best cap/rotor will quicky deteriorate if the wires have higher than normal resistance or the plugs are worn.
     
  18. chuzz

    chuzz Well-Known Member

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    Back in my days at Autozone, we sold a brand called Conrad. They had the brass inserts. The Zone didn't carry them for many applications, but to the customers I sold them too (I THINK mostly GM), I got a lot of positive feedback.
     
  19. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    :points? Surely you jest. They disappeared in 1972.
    If the rotor rotates on the shaft, it most assuredly WILL affect timing, as it still received the high voltage from the center wire, but as the rotor's position wobbles laterally, it will change the time at which it lines up with the individual wire contact in the cap and discharge.
     
  20. KOG

    KOG KOG
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    Timing is a function of switching the coil, not lining up with the cap. But if this one has the switching shutter as part of the rotor, then loose rotor sure will affect timing. Points. Just betrayed my age there, didn't I? I'm so into distributorless ignition now I don't even think about electronic distributors.
     

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