Author Topic: Do Spark Plugs Wear Out?  (Read 276 times)

Online Rosebud

Do Spark Plugs Wear Out?
« on: June 30, 2020, 12:09:05 PM »

Other than obvious visible wear to the electrodes, do spark plugs wear out internally? Over the last few weeks my otherwise easy-starting motor began taking 4 to 5 seconds of cranking before it would fire up. Once started it ran fine. The other day it refused to fire.


Fuel supply seemed fine, 2 to 3 psi on the gauge and the plugs were wet, because of course, I flooded it trying to get it started. I pulled a couple of plugs and got a visible spark on each. The plugs had about 10K miles on them but otherwise looked fine. I know that's pushing things a bit, but as I said, it ran well. Out of ideas I decided to change the plugs because, well, they were (over)due. To my surprise, the engine started right up and has continued to do so. Other than jiggling some wires around under the bonnet in my search for the problem, I have no explanation other than worn-out plugs. Is this possible?
Rosebud
...the sled, not the flower
https://www.facebook.com/PoserMotorSports

Offline 94touring

Re: Do Spark Plugs Wear Out?
« Reply #1 on: June 30, 2020, 12:44:47 PM »
Sounds like you may have fouled the old plugs with an overly rich mixture.

Offline MiniDave

Re: Do Spark Plugs Wear Out?
« Reply #2 on: June 30, 2020, 12:48:05 PM »
Or the coil might be borderline.....new plugs take far less power to fire them.
1989 Cooper Racing Green
2009 Clubman S
2004 Audi Allroad 2.7 TT

Online Rosebud

Re: Do Spark Plugs Wear Out?
« Reply #3 on: June 30, 2020, 01:06:40 PM »
Sounds like you may have fouled the old plugs with an overly rich mixture.
I’m sure they weren’t fouled. I checked them frequently, every couple of weeks. They were always a nice, light chocolate brown color—no sign of fouling. Plus, my O2 gauge confirmed my mixture was good.
Rosebud
...the sled, not the flower
https://www.facebook.com/PoserMotorSports

Online Rosebud

Re: Do Spark Plugs Wear Out?
« Reply #4 on: June 30, 2020, 01:27:52 PM »
Or the coil might be borderline.....new plugs take far less power to fire them.
I suppose that’s possible. I have a Pertronx Flamethrower coil and a 1-2-3 distributor and always suspected I needed a big spark.

When I was having alternator problems and my battery would get below 12.8v I would get an occasional missfire. Below 12.5v the misfire was almost constant. Alternator and battery good now, but I’ll keep my eye on the coil.
Rosebud
...the sled, not the flower
https://www.facebook.com/PoserMotorSports

Offline MiniDave

Re: Do Spark Plugs Wear Out?
« Reply #5 on: June 30, 2020, 01:48:09 PM »
Dan's engine is built pretty well, and he went with a really powerful coil setup (60K volts IIRC) , now as he adds more power producers like the turbo he's still got plenty of coil to handle them.....

but yes, plugs can develop internal resistance as they age.
1989 Cooper Racing Green
2009 Clubman S
2004 Audi Allroad 2.7 TT

Offline 94touring

Re: Do Spark Plugs Wear Out?
« Reply #6 on: June 30, 2020, 05:23:04 PM »
Regarding coils, do you have the correct ohms for the dizzy and/or ballast wiring?  I do use a 60k volt flamethrower at 3ohms for my csi dizzy, and the new dizzy and amethyst system require 1.5 ohms.  The new 60k volt 1.5 ohm coil just arrived for when I set the new system up.  My understanding is if you have a 3 ohm coil on a 1.5 ohm system you'll get weak spark.

Online Rosebud

Re: Do Spark Plugs Wear Out?
« Reply #7 on: June 30, 2020, 06:48:02 PM »
Regarding coils, do you have the correct ohms for the dizzy and/or ballast wiring?  I do use a 60k volt flamethrower at 3ohms for my csi dizzy, and the new dizzy and amethyst system require 1.5 ohms.  The new 60k volt 1.5 ohm coil just arrived for when I set the new system up.  My understanding is if you have a 3 ohm coil on a 1.5 ohm system you'll get weak spark.


Hmm… I DO recall something about a 1.5 vs. 3.0 ohm coil when I was building my car. I'll check my notes and see what I ended up with. I also wrote down the procedure for checking the coil's resistance. Into the archives I go… Will advise.
Rosebud
...the sled, not the flower
https://www.facebook.com/PoserMotorSports

Offline 94touring

Re: Do Spark Plugs Wear Out?
« Reply #8 on: June 30, 2020, 11:24:06 PM »
Just went to the 123 website and looked up mini dizzies. The specs provided say do not use a coil below 1ohm.  If you do use a 3ohm and especially if you have a resistor wire for some reason (though I don't think your car would if I recall the year) then trying a 1.5ohm may be the way to go.

Online Rosebud

Re: Do Spark Plugs Wear Out?
« Reply #9 on: June 30, 2020, 11:57:55 PM »
If you do use a 3ohm… then trying a 1.5ohm may be the way to go.
So, generally speaking, does a lower resistance coil mean a bigger spark, provided the dizzy can handle it?
Rosebud
...the sled, not the flower
https://www.facebook.com/PoserMotorSports

Offline 94touring

Re: Do Spark Plugs Wear Out?
« Reply #10 on: July 01, 2020, 12:19:19 AM »
That's how I understand it. Later models have the pinkish resistance wire and some dizzies have built in resistance.  Going 3 on something with built in resistance will zap a lot of...zap. 
« Last Edit: July 01, 2020, 12:21:49 AM by 94touring »

Offline 94touring

Re: Do Spark Plugs Wear Out?
« Reply #11 on: July 01, 2020, 09:19:59 AM »
I just ordered the 60115.  Now it's not the traditional round coil, I think Bruce and I refer to it as the star wars coil.  It does mount nicely off the clutch housing.  I also run gapless brisk spark plugs.  On my rotary with an ignition amp I gained something like 10hp to the wheels and it feels smoother in general.  I also burn 400cc's of water and a lot of fuel at very high boost.  The mini will also be getting water injection so it's crucial I have strong spark.  Plus it just runs better. 

Online Rosebud

Re: Do Spark Plugs Wear Out?
« Reply #12 on: July 01, 2020, 10:27:14 AM »
I just ordered the 60115.  Now it's not the traditional round coil, I think Bruce and I refer to it as the star wars coil…
Who knew there were so many options? I think when I ordered my Flame-Thrower I just said "Gimme the shiny chrome one.”
« Last Edit: July 01, 2020, 12:32:16 PM by Rosebud »
Rosebud
...the sled, not the flower
https://www.facebook.com/PoserMotorSports

Offline tsumini

Re: Do Spark Plugs Wear Out?
« Reply #13 on: July 01, 2020, 11:30:41 AM »
If you do use a 3ohm… then trying a 1.5ohm may be the way to go.
So, generally speaking, does a lower resistance coil mean a bigger spark, provided the dizzy can handle it?
Given that I = V/R a lower resistance gives higher amperage implying stronger spark.

Offline tsumini

Re: Do Spark Plugs Wear Out?
« Reply #14 on: July 01, 2020, 11:37:37 AM »
You also may want to check the required gap from the pickup and rotor. My Pertronix was supposedly a drop in and go but had to be modified to get the required .030 gap.

Offline BruceK

Re: Do Spark Plugs Wear Out?
« Reply #15 on: July 01, 2020, 01:18:41 PM »
I just ordered the 60115.  Now it's not the traditional round coil, I think Bruce and I refer to it as the star wars coil.  ...

Not Star Wars.    Space Invaders!!

In cross section the coil looks like it belongs in the game.

1988 Austin Mini
2002 MINI Cooper S
2007 Triumph Bonneville
1992 Toyota LiteAce