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Thread: 1100rt spark plug question

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  1. #1
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    1100rt spark plug question

    Finally found the Autolite 3923 plugs after ck'g Autozone and O'reillys at Pep Boys.
    Got the double platinum for longer life.
    Question is on the gap. With the stock plugs, dual prong it's only .031, but the Autolites are about .044 out of the box. For you guys who have installed these, did you leave that gap or change it?
    Tks.

  2. #2
    Benchwrenching PGlaves's Avatar
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    I'd go .035 to .040
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

  3. #3
    Registered User roger 04 rt's Avatar
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    Mine came the same way. I don't know if it is best but I try to have the face of the tang parallel to the top of the center electrode. Given the amount of movement needed I found that difficult, one plug needed a slight compound bend, the other plug ended up with the ground extended well beyond the center electrode. I used them but didn't like what I went through.
    Last edited by Roger 04 RT; 12-02-2012 at 01:14 PM.

  4. #4
    Rally Rat
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    I use .035".

  5. #5
    MOA #24991 Pauls1150's Avatar
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    Gap is determined somewhat by what the ignition system can crank out (along with fuel mix, compression, etc.). Cars' ignitions are historically much more robust than bikes'. If you can't reliably and repeatedly light the fires, it ain't gonna run right.

    Been a while, but I recall setting mine to .032 with zero issues, and let 'em wear - which they did quite slowly, and better than the factory Bosches (which I've never had "fine running" with anyway).

    Note that on some auto plugs, the manufacturer clearly intends that the gap is NOT to be changed - not only is the ground electrode Quite stiff, but it can be really easy to crack the center porcelain.

  6. #6
    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by PGlaves View Post
    I'd go .035 to .040
    Hi Paul, I am curious on why the larger than spec gap to start off with a new plug.

    BMW factory manual states 0.8mm (0.0315) to a max of 1.0mm (0.039) so 0.035 is right in the middle.

    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  7. #7
    IBA #44567 Ken F's Avatar
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    Possibly due to the fact that it's an electronic ignition?
    IBA #44567
    "Two things are infinite: the universe and human stupidity; and I'm not sure about the the universe."
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  8. #8
    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by Ken F View Post
    Possibly due to the fact that it's an electronic ignition?
    Not sure I understand. It was electronic when BMW recommended a smaller gap.

    My question for Paul was why go larger on a new plug.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  9. #9
    Benchwrenching PGlaves's Avatar
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    Quote Originally Posted by Happy Wanderer View Post
    Not sure I understand. It was electronic when BMW recommended a smaller gap.

    My question for Paul was why go larger on a new plug.
    Crisper spark. Voltage builds to jump the gap. Larger spark too.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

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