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spark plugs

Discussion in 'XJ Technical Chat' started by jerry57g, Aug 3, 2021.

  1. jerry57g

    jerry57g New Member

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    Having a hard time finding plugs for an 82 750 Maxim. All I have been able to find locally are the type with the nut on top. I need the type with the stud on top. I know you unscrew the nut on some models. But I can't find a cross reference. Contemplating on putting on different caps but would rather have the correct plug type. Any info/help is greatly appreciated.
     
  2. Jeff Witt

    Jeff Witt New Member

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    I ordered some NGK's directly from NGK for my 83 XJ650 on July 30th they are shipping via USPS.
     
  3. jerry57g

    jerry57g New Member

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    Were they the kind that you remo ve the top nut and use what is called stud type of plugs?
     
  4. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    NGK will automatically substitute the RESISTOR version (BPR7ES) when you order the discontinued stock non-resistor plug (BP7ES). The stock non-resistive plug has a removable cap nut; the replacement resistive BPR7ES has a fixed (non-removable) terminal nut, which won't work with most of their replacement plug caps(!).....and besides, if you use resistive plugs, you shouldn't be using the stock resistive plug caps, you need to use non-resistive plug caps (which we have) or just rubber boots and a terminal on the end of the plug wires.

    Their high-performance IRIDIUM spark plug (BPR7EIX) has a removable nut (= the threaded stud), but again, it is a resistive plug, which means you shouldn't use the resistive plug caps with them, either.

    We still have some of the original BP7ES plugs in stock......non resistive, threaded stud on top.
     
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  5. Dan Gardner

    Dan Gardner Well-Known Member Premium Member

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    That really stinks that they discontinued the BP7ES. Now we are going to have to start hoarding those, too.
     
  6. Jeff Witt

    Jeff Witt New Member

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    The ones I got directly from NGK are the bpr7es 5534 they do have the threaded on stud so it can be removed easily. Can someone direct me to an article or post about the resistive caps on the plug wires? I do not totally grasp the concept of the resistance in the wire and what it does.

    Regards,
    Jeff
     
    Last edited: Aug 31, 2021
  7. Dan Gardner

    Dan Gardner Well-Known Member Premium Member

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    There is some good info here:
    http://xj4ever.com/catalog/d-6-ignition.html

    The punch line is that the total resistance in the system needs to be in spec.

    In math-like terms, for example:
    5K Ohm cap + Zero Ohm (non-resistor) plug = Zero Ohm (non-resistor) cap + 5K Ohm plug = 5K Ohms total.
     
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  8. XJ550H

    XJ550H Well-Known Member Premium Member

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    time to get the 0 ohm caps and use resistor plugs
     
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  9. Jetfixer

    Jetfixer Well-Known Member

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    I use Autolite 63 sparkplug with removable caps ,these are equivalent to the NGK . Autozone has them ...of course try to explain it is for a motorcycle to the dude working there.
     
  10. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    The "ball" unscrews from the top of the plug. Even on automotive sparkplugs.
     
  11. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    The Autozone computer system is slightly better than many of the other major chain parts stores, but you're still dependant on the parts counterperson knowing how to work the system in ways that it isn't intended to be worked. NAPA generally will cross refrence better.
    In any case asking for a part by the manufacturer's part number works at most places.

    I miss the days of being able to pull common wear parts off of a shelf myself. GI Joe's had an entire aisle of sparkplugs, and a cross-refrence book every five feet.
     
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  12. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    The resistance does two things. One is common across all engines, and the other is specific to TCI ignition systems (which our bikes have).

    The first function is to suppress Radio Frequency interference. This is mainly an issue for automobiles so you don't hear the ignition firing over your AM radio, but it also prevents interfernace that could potentially interfere with a solid-state ignitor (TCI, CDI, HEI).
    The second function is to fine-tune the spark duration in a TCI ignition system. A longer spark (caused by a higher resistance) provides for a more complete burn and improves the effeciency and power (slightly) in combination with a larger valve overlap. Kevin Cameron has a great article about that topic in his book, "Top Dead Center 2."
     
  13. Huntchuks

    Huntchuks Well-Known Member

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    Not quite so. I bout plugs with that assumption and the fat electrodes were fixed. I had to bring them back and get different ones. If you look them up you can see some have removable caps and some don't.
     
  14. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Well....when the heck did that change?! Dumb. Ughhh :p
     
  15. Antothoro

    Antothoro Member

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    Got any suggested aftermarket spark plug wires?
     
  16. Jetfixer

    Jetfixer Well-Known Member

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    Yes I use Bosch VW beetle four cylinder spark plug wires ....you cut off ends ( I have a beetle so had a set I was not using ) I use 81-83 CB 750 coils .
     
  17. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    You'll need aftermarket coils too, or a plug wire splice, or a dremel and some epoxy. The OEM wires are moulded into the coil cases.
     
  18. tabaka45

    tabaka45 Well-Known Member

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    OK, so what happens if I run resister plugs in my 85 XJ7ooN?
     
  19. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Spark duration increases. Spark voltage decreases.
    Change to non-resistor caps and the original relationship is maintained.
     
  20. tabaka45

    tabaka45 Well-Known Member

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