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Reading Spark Plugs
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TOPIC: Reading Spark Plugs

Reading Spark Plugs 8 years, 9 months ago #14811

  • AgRacer
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Doing some off season preventive maintenance since I never did any after getting the car.

I pulled the plugs for final inspection of the ignition system. Cap, rotor, and wires all visual inspect fine. Plugs, not so much. Any way you can read these plugs? One big noticeable thing is that #2 seems to be drier than the others.

plugs.jpg


After doing some research, I plan on replacing them with NGK BPR6ES plugs in preparation for my dyno session. I was going to do an entire tune up on the ignition system, but after pulling the timing belt covers, I think I should take this opportunity to do some real preventive maintenance since I have absolutely no idea how old the timing and balance belts are.
J. Stanley
NASA-SE Region 944 Spec Series Director
Yellow #60

Re: Reading Spark Plugs 8 years, 9 months ago #14812

  • joeblow
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  • Seasoned Racer
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Reading plugs is much more than surface pictures like yours can cover. Further pic #4 seems to be in different lighting conditions as the others so that might make it harder to compare.

That all being said it looks like you are burning oil which can be from leaky valve stem seals, excessive blow-by getting past the oil breather and into the intake (look for an oily intake bellows) or blown piston rings and/or worn cylinders.

It also looks like you may be running too cold a plug or idling too much without giving the plugs a good burn off.

Once you get all the issues worked out and get a plug that is close in temperature then you can REALLY start reading plugs which has nothing to do with the outside of the plug and everything to do with the ceramic down deep in the plug that you really cant take a pic of. There is a ring that develops on the ceramic deep in the plug that old racers call the 'power ring' which helps to fine tune the ideal mixtures. The problem is that this ring can get covered up after idling or normal driving so it has to be done quickly on fresh plugs. But this is beyond the scope of this reply....
Old Racer!

Re: Reading Spark Plugs 8 years, 9 months ago #14813

  • AgRacer
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Thats some good insight. The plugs currently in the car are Bosch WR8DC+ which I think run a little cooler than what is originally specified in the WR7DC.

The car has mostly been idled in the driveway since my last race in October. There is a decent amount of oil residue in the intake almost to the point of pooling. I describe it in my other trouble shooting thread on the vacuum system. Ill take a pic of it and post it later.

And sorry about pic #4, I was starting to get artistic with the lighting.
J. Stanley
NASA-SE Region 944 Spec Series Director
Yellow #60

Re: Reading Spark Plugs 8 years, 9 months ago #14814

  • joeblow
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Well that matches what I see from the pics. If you get the blow-by in check and run the hotter plugs and start doing some power runs to keep the plugs clean, I think you will be in the ballpark.

Good luck with it.
Old Racer!
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