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spark plug against block

Discussion in 'General Chevy & GM Tech Questions' started by 4x4squared, Feb 22, 2013.

  1. 4x4squared

    4x4squared Member 2 Years 100 Posts

    Hey guys, been a while since i been on here but i have a question and figured id come back to get your input lol. I was in class and i mentioned holding a plug against the engine block (on older vehicles without all the electronics) to test for spark. My instructor then went on to tell me that is one of the worst things that you could do to your engine because rather than running out and grounding, the shock runs through the block and will go into grease, swirl around and fuse things like cam bearings right to the shaft.... Ive done this probably hundreds of times and im quite sure my cam and crank are still spinnin just fine lol. Am I wrong here?
  2. RayVoy

    RayVoy Active Member 2 Years 1000 Posts

    Well, I've not heard that; but it can be hard on the coil during the time the plug is not grounded.

    I've been using a jumper cable, connecting the plug threads to the neg battery terminal, then the plug is always grounded.
  3. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    First time I've ever heard of that.
    Electricity will always take the path of least resistance, I guess in theory electricity could travel across the crank and cam bearings leaving scorch marks that could possibly fuse the bearings.
    I'd really have to see that one happen to be a true believer though, I've been using the same method as you for many years on all types of engines.
  4. Pikey

    Pikey Active Member Staff Member 2 Years ROTM Winner 1000 Posts

    I had never heard of that happening. I could be wrong but, doesn't grease act as an insulator? I have never attempted to run electricity thru grease so I am not sure. I have done that multiple times on older vehicles and never had any issues. Electricity takes the path of least resistance. I would assume that the metal of the block and the ground cable would be less resistance than a greased bearing. I don't want to say what school you are attending, but I live in Michigan also and I bet that I can figure it out with 3 guesses! I may be attending the same school, just a different campus! The instructors I have now are good (since the ABET certification for engineering) But, some of the guys I have come across have no real world experience. @RayVoy , I have never thought of the jumper cable thing. I do have a spark tester that looks like a plug but is clear so you can see the spark. I may try that in a jamb.
  5. csltrains96

    csltrains96 Rockstar 100 Posts

    What do you think the spark plug is using for a ground when it is installed? The block!!!!
  6. Chris Miller

    Chris Miller Rockstar 100 Posts

    The plug already grounds against the block no matter what, haha! That instructor must've been in the wacky tobaccy that day.

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