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Thread: 1100rt spark plug question

  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
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    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".

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    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."
    -Albert Eienstein

  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

  10. #10
    Registered User rxcrider's Avatar
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    Fine tip spark plugs can, in theory, be gapped larger for the same ignition. Due to the materials and geometry, you should be able to jump the same gap with fewer volts. Therefore, you can increase gap to get a larger spark at the same voltage.

  11. #11
    Day Dreaming ... happy wanderer's Avatar
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    Thanks guys. This makes sense now. Especially on such lean running engines.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  12. #12
    Registered User roger 04 rt's Avatar
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    With my 1150RT now running really well on a richer mixture, I'm going to switch back to the stock plugs and see how that goes. And because I don't put much mileage on I'm thinking of gaping at 0.035".
    Last edited by Roger 04 RT; 12-06-2012 at 02:55 PM.

  13. #13
    Day Dreaming ... happy wanderer's Avatar
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    Quote Originally Posted by Roger 04 RT View Post
    With my 1150RT now running really well on a richer mixture, I'm going to switch back to the stock plugs and see how that goes. And because I don't put much mileage on I'm thinking of gaping at 0.035".
    Why bother? Stock plugs are much more expensive than the alternatives that seem to work better in most cases anyway.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  14. #14
    Registered User roger 04 rt's Avatar
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    Quote Originally Posted by Happy Wanderer View Post
    Why bother? Stock plugs are much more expensive than the alternatives that seem to work better in most cases anyway.
    Mainly because I want to see if there is any discernible difference between the autolites which I have now and the NGK/Bosch, with the richer mixtures I run now.

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    Quote Originally Posted by Roger 04 RT View Post
    Mainly because I want to see if there is any discernible difference between the autolites which I have now and the NGK/Bosch, with the richer mixtures I run now.
    If it is running fine now, how will you know if it improves with a swap to the high priced plugs? I've run copper Autolite plugs in my 95 r1100r for the last 6 years without any trouble. Although I don't put a lot of miles on them, every year I put in a new set, the old ones look perfect. They cost about $1.50 each at WalMart.
    regards,
    Mark

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