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Why do spark plug leads wear out

Discussion in 'Hobby Electronics' started by Phil, Sep 25, 2003.

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  1. Phil

    Phil Guest

    The subject says it all. What is it that makes spark plug leads wear out?
    (other than mechanical wear and tear)

    Cheers, Phil
     
  2. Ken Taylor

    Ken Taylor Guest

    Chemical wear and tear.

    Ken
     
  3. Phil

    Phil Guest

    I hear they are supposed to have a built in resistance. I don't see why they
    should have that at all. Can't they make a lead made of the usual copper
    material that won't wear out so quickly? You don't see everyone asking to
    change their whole wiring loom because of wear and tear so why should SP
    leads be any different?
     
  4. mc

    mc Guest

    yes and HV wear and tear..sooner or later the insulation medium looses
    its dielectric strenght ..hence the HV voltage being passed through is
    reduced ..hence lower sparks ..and sometimes to the point ...no sparks
    at all..when the spark punctures through the lead and never gets to the
    plug..hence you get a "miss" in one or more of your cylinders..I had
    that happen on a mazda ..bloody expensive to replace ..
     
  5. Phil Allison

    Phil Allison Guest


    ** There is severe radio interference with copper leads.

    They used to fit 15 kohm HV resistors in the old days.



    Can't they make a lead made of the usual copper

    ** See above.


    ** High voltages are different.




    ........... Phil
     
  6. I bet if you had megavolts running through all day you would breakdown
    too...Add to that being in a very hostile environment that has plenty of
    heat and shit around. Hey, sounds like my day to day job..
    Just did a timing belt in my newish Mazda929. 1200bucks to replace. Rang
    mazda coz i thought i was getting fucked over by the mechanic, 800something
    just for the belt kit plus all the seals and gaskets and shit. I'm going to
    buy me a VX commodore next week, screw this imported crap. Mind you, the
    mazda is very very nice to drive and is about the closest i will ever get to
    owning a BMW......
     
  7. Some lead resistance is actually good at higher voltages as you can expect a bettter hotter spark , especially in the older ignition
    systems. This can be easily seen on a scope if you compare a copper lead to a carbon lead and is quite dramatic.
    The mechanics are given this view as a way of understanding the effect but maybe not completly correct, the resistance causes the
    leading electrons to back up when they see the resistance and then the higher resultant voltage that follows causes a denser and
    more intense spark. I thought this explanation was novel when I first heard it and it takes me back to the old days when we used to
    hold a couple of leads about 6mm from the plugs to get a bomb to start, electrons back up like a flock of sheep at a cliff until
    the pressure from the mob behind becomes to much and you get a lot more over the cliff in one single package instead of the dribble
    you would get from a single file.
    Copper leads can also cause inductive coupling or crossover between leads and stainless steel leads were used in racing cars at one
    stage to stop this.


    I bet if you had megavolts running through all day you would breakdown
    too...Add to that being in a very hostile environment that has plenty of
    heat and shit around. Hey, sounds like my day to day job..
    Just did a timing belt in my newish Mazda929. 1200bucks to replace. Rang
    mazda coz i thought i was getting fucked over by the mechanic, 800something
    just for the belt kit plus all the seals and gaskets and shit. I'm going to
    buy me a VX commodore next week, screw this imported crap. Mind you, the
    mazda is very very nice to drive and is about the closest i will ever get to
    owning a BMW......
     
  8. PW

    PW Guest

    Ozone damage to the dielectric material surrounding the conductive
    core allows the high voltage to leak and/or arc after a number of
    years.
     
  9. If you leave them suspended in mid air they won't wear out for years
    and years. This is because there is very little breakdown of the
    rubber in that case. (No severe voltage potentials across the
    insulation if they are not touching grounded objects.)
     
  10. John Mackesy

    John Mackesy Guest

    <good points snipped for brevity>
    Just did a timing belt in my newish Mazda929. 1200bucks to replace.


    Coincidentally, I did the same job on our '92 Ford Laser (Mazda clone) a
    couple of days ago. Timing belt needs to be changed every 100,000 Km; I've
    just done it for the second time at 200,000 Km. $47.00 for the timing belt,
    $32.00 for the alternator/water pump and power steering belts. No seals
    required, took a couple of hours.

    Assuming the 'newish Mazda' is a V6 a greater degree of difficulty seems
    reasonable, but $1200 seems a bit steep. Did the belt break and cause
    secondary damage?

    John Mackesy
     
  11. Rob Judd

    Rob Judd Guest

    Sounds to me like the valves were bent.

    Rob
     
  12. Nope, no bent valves thank god. V6 engine. The belt didn't actually break, i
    must slipped somehow, maybe stretched because of the oil leaking in to the
    timing cover. It snapped the tensioner bolt and that was about the worst of
    the damage. The cost is in the belt kit, genuine only. 860 odd dollars.
    Stick on 5 hours of mechanics labour plus new seals and your pushing it
    close to 1200bucks. Bye Bye mazda, hello VX commodore wagon...
     
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