.050" spark plug gap ??
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Cadillac Seville / Cadillac Eldorado Forum Discussion, .050" spark plug gap ?? in Past Cadillac Vehicle Discussion; Bump. Hi guys! So, yesterday I was looking at my spark plugs-- well, the 5 of them that I could ...
  1. #1
    geegeeburr is offline Cadillac Owners Member
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    .050" spark plug gap ??

    Bump.

    Hi guys! So, yesterday I was looking at my spark plugs-- well, the 5 of them that I could get to. The ones I pulled looked basically like the one in the picture in post #3 of this thread. Maybe the pointy part (electrode?) was just a tad longer. I tried to measure the gap with my regular tape measure, and it looked to me like it was about 3/32. Brother and dad, who were one the phone, seemed to think that sounded too big. One of the plugs also had a little bit of sort of caked/crusty gray stuff on it. On the part with the 90-degree angle. Brother said that was probably fine. My neighbor thought the plugs looked fine.

    So, got some questions:

    1. This forum says the gap should be .06. If my math is right, mine is closer to .09, which couldn't possibly be good, right? Bad for your coils, because they have to work harder to make the spark jump across?

    2. The spark plugs are attached to the ignition coils. Do they only fire when you are starting the car? Or are they what causes all of the tiny explosions that make the car go? So, when someone says your firing order is 1,2,7,3,4,5,6,8- that is referring to the spark plugs, right? And that is happening the whole time your car is running?

    3. When I put mine back in, I was just using a socket extender, and tightening them hand-tight. My brother told me to put a ratchet on there and turn them a tiny bit more, maybe 1/8 to 1/4 of a turn, but don't force them. But I saw somewhere where Ranger said they are supposed to be tightened to 13 foot-pounds. Did I screw them up by not using a torque wrnch?

    4. What is anti-sieze? Just lubricant so they'll come out again? I didn't put any.

    Thanks.

    PS_ I don't know if/when the plugs were last changed. I did notice that they said Delco.

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    Submariner409's Avatar
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    Re: .070 spark plug gap

    The correct AC Delco Platinum spark plugs #41-950 come pre-gapped to the proper .050". Torqued to 13 lb/ft with a tad of anti-seize on the first 3 threads. This forum does NOT give the plug gap as .060" - if someone stated that, they are mistaken.

    Use this graphic to correctly connect the coils to the spark plugs. You might seriously consider a new set of AC Delco spark plug cables, too - those things are NOT forever.

    If you did not use a torque wrench, the plugs should be tightened with the socket handle to - ahem - "pretty tight but nowhere near squeak tight".

    Did you ever get a real GM service manual or subscribe the car to www.alldatadiy.com ??? There's every bit of your info in there ..........

    Firing order - before you get into firing orders and sequences you'll need a basic understanding of the Otto 4-cycle ignition/timing theory. An 8 cylinder 4-cycle engine fires only 4 spark plugs - power pulses - per crankshaft revolution. The plug for each cylinder fires ONLY at the time of exact crankshaft rotation/piston location/fuel delivery/valve openings to supply a controlled fuel burn and power pulse. The Otto cycle is " intake - compression - power - exhaust " related to the piston travel in the cylinder: The piston is pulled down in the cylinder by the connecting rod/crankshaft; this creates a vacuum in the cylinder and, as the valves operate and the fuel injector trips, fuel mixture flows into the cylinder due to atmospheric pressure; The valves close and the piston travels up in the cylinder, compressing the fuel/air mixture, the spark plug fires at the proper instant to begin the fuel burn which pushes the piston down in the cylinder (power stroke). The exhaust valve opens and the crankshaft/connecting rod pushes the piston up in the cylinder, expelling the spent exhaust gases. The exhaust valve closes, the intake valve opens, the piston starts down and the cycle repeats.

    Watch this - all of it - and imagine that it's exactly 1/2 of your engine ............

    http://www.youtube.com/watch?v=OXd1PlGur8M

  4. #3
    geegeeburr is offline Cadillac Owners Member
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    Re: .070 spark plug gap

    Quote Originally Posted by Submariner409 View Post
    The correct AC Delco Platinum spark plugs #41-950 come pre-gapped to the proper .050". Torqued to 13 lb/ft with a tad of anti-seize on the first 3 threads. This forum does NOT give the plug gap as .060" - if someone stated that, they are mistaken.

    Did you ever get a real GM service manual or subscribe the car to www.alldatadiy.com ??? There's every bit of your info in there ..........

    Firing order - before you get into firing orders and sequences you'll need a basic understanding of the Otto 4-cycle ignition/timing theory. An 8 cylinder 4-cycle engine fires only 4 spark plugs - power pulses - per crankshaft revolution. The plug for each cylinder fires ONLY at the time of exact crankshaft rotation/piston location/fuel delivery/valve openings to supply a controlled fuel burn and power pulse. The Otto cycle is " intake - compression - power - exhaust " related to the piston travel in the cylinder: The piston is pulled down in the cylinder by the connecting rod/crankshaft; this creates a vacuum in the cylinder and, as the valves operate and the fuel injector trips, fuel mixture flows into the cylinder due to atmospheric pressure; The valves close and the piston travels up in the cylinder, compressing the fuel/air mixture, the spark plug fires at the proper instant to begin the fuel burn which pushes the piston down in the cylinder (power stroke). The exhaust valve opens and the crankshaft/connecting rod pushes the piston up in the cylinder, expelling the spent exhaust gases. The exhaust valve closes, the intake valve opens, the piston starts down and the cycle repeats.

    Watch this - all of it - and imagine that it's exactly 1/2 of your engine ............

    http://www.youtube.com/watch?v=OXd1PlGur8M
    Thanks, Sub!

    Re the .06: Sorry, my statement lacked specificity. I should have said, "I read a bunch of threads about this, with several people saying their manual said .05, but (fill-in-the-blank) said .06, and several people said the '97 was an exception to the .05, and the general consensus seemed to be that .06 was fine." Anyway, that was what I got from reading through a bunch of threads. Not that this website, itself, said .06.

    No, didn't get the service manual because right after that was when we figured out the head gaskets really were going, and there didn't seem to be much point, then. Didn't really think I'd be even considering still working on it...

    Okay, that video is AWESOME. I am going to have to watch it, and re-read your explanation, a LOT more times. Thanks!

    ----------

    Okay, just saw your coils/plugs diagram. Out of curiosity only, why do they fire in that order? is it because of the locations of the pistons on the crankshaft? Or is it so that coils which are next door to each other are rarely carrying current in sequence?

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    Re: .070 spark plug gap

    Quote Originally Posted by geegeeburr View Post
    why do they fire in that order? is it because of the locations of the pistons on the crankshaft?
    Yep - actually, the number of rotational degrees between crank throws - look at the video again - the 4-cylinder engine has 2 pistons paired, so they can fire 180 degrees apart, while the V-8 has the pistons staggered around the crank centerline so they can be timed to fire 90 degrees apart. The more pistons (in a 4-cycle engine) the smoother the engine is - in a V-10 there's a power pulse every 72 degrees, V-12 it's every 60 degrees, in a V-16 every 45 degrees.
    geegeeburr likes this.

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    Re: .050" spark plug gap ??

    Quote Originally Posted by geegeeburr View Post

    1. This forum says the gap should be .06. If my math is right, mine is closer to .09, which couldn't possibly be good, right? Bad for your coils, because they have to work harder to make the spark jump across?
    .050 is correct. I doubt yours are at .090. I don't think the spark could jump that gap.


    3. When I put mine back in, I was just using a socket extender, and tightening them hand-tight. My brother told me to put a ratchet on there and turn them a tiny bit more, maybe 1/8 to 1/4 of a turn, but don't force them. But I saw somewhere where Ranger said they are supposed to be tightened to 13 foot-pounds. Did I screw them up by not using a torque wrnch?
    Every nut and bolt in the car has a torque setting. Some are critical, most are not. Spark plugs are not. Just snug 'em down good.


    4. What is anti-sieze? Just lubricant so they'll come out again? I didn't put any.
    Anti-Seize is a silvery paste that prevents the steel threads from galvanic action and seizing to the aluminum head. A/C Delco says that their plugs are made of a corrosion resistant shell and thus do not need anti-seize. The choice is yours.

    PS_ I don't know if/when the plugs were last changed. I did notice that they said Delco.
    Are they misfiring?

    P.S.
    NEVER try to gap or read the gap with a ruler. You need a spark plug gaping tool (feeler gauge). There several on the market.


  7. #6
    JimD is offline Cadillac Owners Connoisseur
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    Re: .050" spark plug gap ??

    Quote Originally Posted by Ranger View Post
    .050 is correct. I doubt yours are at .090. I don't think the spark could jump that gap.
    With clean and dry and otherwise as new ignition system parts, the coil (transformer) secondary winding can develop sufficient voltage to arc over a gap larger than 0.090". At least at idle and probably much higher throttle blade openings.

    Misfiring will certainly occur as you get closer to redline engine RPM simply because the coil (transformer) primary does have sufficient time to generate the flux density required.

    When you move from a four coil (transformer) system to an eight coil (transformer) system, each coil (transformer) has twice as long to develop the necessary flux density.

    Makes a person wonder how we were ever able to obtain any kind of performance from an eight cylinder engine with a single coil (transformer) ignition system.

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    geegeeburr is offline Cadillac Owners Member
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    Re: .050" spark plug gap ??

    TY, Ranger!
    Quote Originally Posted by Ranger View Post

    Are they misfiring?
    I just got that one random misfire code, and the rough idle, but the idle I think is the head gasket issue. The whole spark plug question was more academic than anything- I was in there looking around at stuff, and figured what the hell, I'll try to check the spark plugs. But that brought up questions.

  9. #8
    Submariner409's Avatar
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    Re: .050" spark plug gap ??

    Quote Originally Posted by JimD View Post
    Makes a person wonder how we were ever able to obtain any kind of performance from an eight cylinder engine with a single coil (transformer) ignition system.
    Remember your old Sun dwell tach and aching back ?

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    Re: .050" spark plug gap ??

    Quote Originally Posted by Submariner409 View Post
    Remember your old Sun dwell tach and aching back ?
    Not fondly.
    In fact with new breaker points, I would set the dwell angle very slightly on the low side because as the rubbing block wore down, the dwell angle would increase.

    My (homemade) dwell meter went to the landfill over twenty years ago along with a vacuum gage, timing light, and a box of Holley jets and valves.

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    geegeeburr is offline Cadillac Owners Member
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    Re: .050" spark plug gap ??

    Quote Originally Posted by JimD View Post
    Misfiring will certainly occur as you get closer to redline engine RPM simply because the coil (transformer) primary does have sufficient time to generate the flux density required.

    When you move from a four coil (transformer) system to an eight coil (transformer) system, each coil (transformer) has twice as long to develop the necessary flux density.
    So, as you go faster, the spark plugs fire faster, causing the crankshaft to turn faster, then? And when you say RPM, that (rotations) refers to rotations of the crankshaft? And because this is an 8-coil system, 4 coils get to take a break every other rotation? So, if the crankshaft rotated exactly 2 times, # 1,2,7, and 3 would be responsible for causing the first rotation, and #4,5,6,and 8 would be responsible for the second rotation?

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    Re: .050" spark plug gap ??

    So, as you go faster, the spark plugs fire faster
    Correct

    causing the crankshaft to turn faster, then?
    Incorrect. The plugs are firing faster BECAUSE the crankshaft is turning faster. They are not causing it. The engine wants to run at full throttle aka WOT (Wide Open Throttle). It is controlled by chocking down the air intake. Open the throttle plate and allow it to ingest more air and it will run faster. Remove the TB and it will run at it's full potential, but uncontrolled.

    Your engine is actually a 4 coil (waste spark) system . Each coil services 2 plugs.
    http://en.wikipedia.org/wiki/Wasted_spark

    Yes, RPM refers to rotations per minute of the crankshaft. Sort of a speedometer for the engine.

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    geegeeburr is offline Cadillac Owners Member
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    Re: .050" spark plug gap ??

    Okay, so here's another question. I'm driving around with leaking head gaskets, so exhaust is getting in the cooling system, and coolant is coming out the exhaust. So if I understand right from some stuff I've read, that means the engine is burning coolant as well as fuel, which makes the engine have to work harder to get combustion. How does the engine burn the coolant, or is it really just turning it to steam and spitting it out. But also what kind of damage is the water/coolant doing to the combustion parts of the engine? (Other than corroding the bolt hole threads on the head gaskets!) Is it corroding everything inside the engine? And also, if the exhaust is getting into the cooling system, and adding pressure since it's supposed to be a closed system, is it the added pressure that causes overheating, or is it just because exhaust is hot? And do the exhaust gasses remain trapped in the cooling system, so you just keep adding more and more pressure every time you drive, or does the exhaust dissipate over time? Could you alleviate that by driving without the radiator cap? Thank you!

    .....This is not good. Every night I'm doing engine homework. I have a tendency to fixate on projects.....


    Sorry, should have put this in the head gasket thread!

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    rbcoats is offline Cadillac Owners Member
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    Re: .050" spark plug gap ??

    Welcome, I just bought a 1999 Eldorado with 91000 miles on it. I decided to change the plugs and got out the 5 easy ones. I called the parts store and they said the gap was .050. I did use anti-sieze on the new ones. I" am weird that way. This will help the next owner. I used a ratchet when tightening my plugs just snug them up do not over tighten them.
    I need to change the 3 plugs under the coil pack, not up to busting my knuckles just yet!

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    Re: .050" spark plug gap ??

    The engine is "using" coolant. The same as pouring water on a bonfire - the water flashes to steam. No, combustion pressures are not affected in a negative way - in fact, the energy required to turn even tiny amounts of coolant into steam lowers the combustion temperature, thus lowering (but not by much) cylinder pressures. Running without a pressure cap also has no effect on the problem - as the piston moves up and down in the cylinder, remember that it creates both vacuum (intake downstroke) and pressure (power downstroke). Coolant is allowed to enter the cylinder through a head gasket breach - it is flashed to steam and exits through the exhaust valve - at the same time that exhaust gas is being expelled into the cooling system by combustion pressure. As the system fills with more and more gases, pressure rises, the coolant becomes aerated, coolant blows out the cap pressure relief due to overpressure, the water pump stops pumping due to cavitation and the engine overheats. Exhaust gas does not overheat the cooling system - lack of pumping ability does.

    geegee, You need to begin following several other threads on questions close to your car and systems.

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    Re: .050" spark plug gap ??

    How does the engine burn the coolant, or is it really just turning it to steam and spitting it out.
    Just turns it to steam and spits it out.

    But also what kind of damage is the water/coolant doing to the combustion parts of the engine? (Other than corroding the bolt hole threads on the head gaskets!) Is it corroding everything inside the engine?
    No damage. In fact it is actually cleaning the combustion chamber of carbon. If you pull the heads, the leaky cylinder will have the cleanest piston crown, valves and spark plug. Many years ago we used to pour water down the carb to clean out the combustion chamber. I'm sure Sub remembers and probably has done that.

    And do the exhaust gasses remain trapped in the cooling system, so you just keep adding more and more pressure every time you drive, or does the exhaust dissipate over time?
    The exhaust gases remain trapped until the pressure reaches the cap pressure (15-18 lbs). Then it is vented.

    Could you alleviate that by driving without the radiator cap?
    Yes, that would elevate system pressure, BUT it would also lower the boiling point and you would still overheat and expel coolant out the open cap. Remember, the reason for the cap is to pressurize the system. Pressure raises the boiling point. As you can see from the chart below a 50/50 coolant water mix boils at 226 deg. Add 16 psi and you raise that by 41 deg.
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