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Spark Plug numbers and letters

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This topic contains 7 replies, has 0 voices, and was last updated by  Steve Wyeth 12 years, 5 months ago.

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  • November 3, 2012 at 12:54 am #102034

    Darren
    Member

    Getting a spare plug has been on my list for ages as a “To-Do” … was just down at SCA getting some other stuff and thought I’d look for the plug for my bike at the same time. Well, other than there being sh*tloads of them, scanning through looking for mine “NGK R BR7ES” I saw every friggin thing but! Even BR6ES and BR8ES, and some that were “Iridium” with BR6EIS and BR8EIS with a 10x (approx) price tag.

    So, my question is what does one-up and one-down in number indicate? Also, are the premium ones worth it? What’s the diff?

    Thanks in advance
    Razzle

    November 3, 2012 at 4:03 am #231900

    Nick Jackson
    Member

    Good question their Razzle , I just thought it was a part number and didn’t mean much but maybe it does ??

    I used an iridium plug in my Tenere with success but seemed to get no life out of them in the Crf ??

    Nick

    November 3, 2012 at 4:21 am #231901

    Scott Southwell
    Member

    Ok I’m no expert but I was led to believe the number is a heat range with a lower number being a hotter plug.

    November 3, 2012 at 9:56 am #231906

    James Rookyard
    Member

    Yep its the heat range and using the wrong one can lead to destroyed pistons in 2 stroke engines. No doubt it does damage to 4 strokes as well.
    Iridium plugs I can’t answer on, other than they last no longer in my sons KX65 than a standard one.

    November 3, 2012 at 11:35 am #231913

    scott bocking
    Member

    I had a bizarre experience with an iridium plug. I went to buy a replacement and the shop offered me the option of iridium at $25 dollars more ( so i bought it) and my bike hated it. It would miss and run rough so I stuck the old cheapie back in and it purred like a kitten. Maybe a dodgy one but I have since just gone the $6 one and had no issue.

    STM

    November 4, 2012 at 3:59 am #231902

    James Rookyard
    Member

    OK, have done some research. The heat range is determined by the length of the insulator protruding around the electrode. The shorter it is the less insulation and therefore the hotter the spark is. This will lead to pre-detonation if used in the wrong situation. Too cold will lead to fouled plugs.
    Iridium plugs use iridium for the electrode. It can be made thinner than a conventional material and also have a squarer edge to improve the ability to make a good spark for longer.
    The numbering system varies from manufacturer to manufacturer. It reflects the heat range of the plug.

    November 4, 2012 at 7:29 am #231955

    Darren
    Member

    Thanks Jimmy

    Sounds like it’s just best I look for the correct “number” plug and stick to the standard (and not expensive) one.

    Razz

    November 4, 2012 at 11:45 pm #231969

    Steve Wyeth
    Member

    Razz, stick with the stock plug and gap it to 0.60mm. The Iridium are a waste and time and money for our bikes. A nicely jetted bikes runs sweet as a nut on the stock plug. I tried the Iridium and a BR8 but ended up back at the stock plug.

    Always carry a spare in your camelback too. I never needed one but you just don’t know……

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