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Thread: spark plug gap

  1. #1

    spark plug gap

    Tuning an 86 R80RT. 74,000 mi. Replacing plugs with Bosch Super w7dc. The owner's manual calls for gapping at .024. The Bosch plugs call for gap of .032. ?
    The manual also calls for Bosch w7d, not w7dc. Is this an issue? If so, where do you get w7d plugs?
    I've had fairly yucky [tech term] plugs after 8000 mi. But good performance and mileage.
    Also have a 76 R75/6, which does have electronic ignition. Does the same info apply?

  2. #2
    Liaison 20774's Avatar
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    My /7 uses the W6DC variety and the 0.024 to 0.026 is about right. 0.032 is too wide...making for hard starting.

    There seems to be a problem getting these plugs...the numbering has changed to 7591 (W5DC), 7594 (W6DC) and 7500 (W7DC). The important thing is to get plugs that are non-resistor. Nominally, the plug wire caps should be between 1000 to 5000 ohm. There's been quite a bit of discussion about plugs and resistances on various forums. Check out this site for some additional information:

    http://home.jps.net/~snowbum/sparkplugs.htm

    Apparently, these plugs are getting harder to find, at least the non-resistor kind. Bosch is making plugs for their bigger market, cars. There's a lot of good talk about NGC. Here's a mapping from Bosch to NGK:

    http://www.spark-plugs.co.uk/pages/t...chw5a-y6dc.htm

    I have the Dyna III electronic ignition, run W6DC plugs, and have the stock ignition caps (about 5K ohms). Works fine for me...

    "Yucky" plugs might indicate improper carburetion or maybe the ignition system is not "hot" enough and you're not getting the most out of your spark, leaving unburned deposits.

    Kurt in S.A.

  3. #3
    Polarbear Polarbear's Avatar
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    Use something else!

    I have used NGK, Autolite and Champions, all with equal success to anything Bocsh makes. Mine is a R100/7 with electric ignition and 24-28 is the gap always. These other plugs are much easier to find, too. Just cross the numbers in the reference charts. The plugs in my bike seem to last forever. At 300000+ miles, I have tried a few different ones, however and found them all high quality plugs.

  4. #4
    Bosch and NGK seem to be slowly discontinuing some of their non-resistor plugs. I can't get W(5/6/7)DCs anymore and they are not listed in the current Bosch catalog. Today I couldn't get a BP6HS from NGK either. No mre listing for that one either.

    John Collier

  5. #5
    Registered User lkchris's Avatar
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    Quote Originally Posted by paulfinney2 View Post
    The manual also calls for Bosch w7d, not w7dc.
    That's not an issue.

    WR7DC is.

    For those that don't know, Bosch plugs come in the box correctly gapped for your motor. The gap is printed on the box.

    You can check them if you want, but I've never found one needing regapped.

    Forget using inch sizes--this is a German bike.
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S

  6. #6
    Liaison 20774's Avatar
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    The WR7DC is a resistor plug. I would be cautious using it along with all of the other resistances built into the ignition circuit. At least that's what I've been told...

    Kurt in S.A.

  7. #7
    Grammarian no, Rider yes ISAMEMON's Avatar
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    two spark plugs take about 15 seconds to check the gap
    I have twisted wrenches for way too long to believe that out of the box, they are all good
    maybe one in eight might be off,(v-8) but hey, that incorrect gap can cause problems, esp with a tired 2 cylinder motor
    take 15 seconds
    or take a night worth laying in bed, wondering why your bike has a miss at "x" speed or at "x" temperature, and man, you just tuned it, so why miss now

  8. #8
    Liaison 20774's Avatar
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    I'd also suggest running a die over the threads to be sure there's no mismatch with the heads. Might save some headache down the line.

    Kurt in S.A.

  9. #9
    The Bosch box said .032 and that is what the plug gap measured, so I regapped to .024.

    Which plug is hotter - W7D or W6D?

  10. #10
    Liaison 20774's Avatar
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    Answers here...it would appear that the higher number is hotter...

    http://www.euromotoelectrics.com/Spa...PLICATION.html

    I would still discount the gap setting on that web page...use something in the 0.026 range instead...

    Kurt in S.A.

  11. #11
    Polarbear Polarbear's Avatar
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    Why?

    Why would anybody ever want to pay lots for a German plug, which are fine plugs, but certainly no better than Autolite, Champion, etc.etc..and so on. I don't get it. I save money when I can and never, ever have these other brands failed me. Plug gapping is so much "rocket" science that some argue metric vs. US conversions for plug gaps! Somebody's been studying too hard... The plugs will indeed run every bike at several settings without hassle, within reasonable tollerances. The mid twenty "thousanths" range has been a standard for so many bikes over the years, that I thought it was a no brainer for most. I guess not. Some newer models are speading the gaps more, these days, but overall, plugs are designed to perform in a wide window of settings and you simply have to find your engines peak setting. This could be up and down the scale, by several thousanths without any notice to engine performance. And, the last time I looked, I lived in the USA, where I own a BMW of course and I still like my USA math and can still convert to metrics as needed. Don' t ever get convinced that you have to buy German for your bike. You can bet they live in a world market, too and buy their supplies all over God's creation! You'd be surprised to find Japanese bearings in your BMW. They exist, believe me.

  12. #12
    Registered User lkchris's Avatar
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    Written from sheer ignorance.

    Plug gaps are "wider these days" in order to develop more voltage.

    All that 1950s knowledge is obsolete.
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S

  13. #13
    I pull wrenches for a living and I stopped using Champion plugs decades ago. One bad plug out of twenty meant a lot of come backs and a bad reputation for me. That is why I stopped using Champion plugs. Their racing plugs are another matter; but we are talking about consumer plugs.

    I have used Bosch for decades with no problems at all. I have also used Autolite with few problems. NGK was blemish free until three years ago when something changed in the local fuel formulation and I have had three or four complete sets go dead on me. They look fine, they just don't fire under load. That means that those cars were dead and the owners had to tow them back to my shop. I no longer use NGKs either. I can't afford to.

    I sure hope you guys are wrong about airheads and resistor plugs as they are soon going to be NLA.

    Unless you have increased your ignition system's output, stick to the factory specified gap.

  14. #14
    Polarbear Polarbear's Avatar
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    I guess!

    50's etc. knowledge got all of us here today, I suppose. We all have our doubts about everything, I guess. I'm just another blue collar guy, saving my money where it counts, riding happily along without issues most of the time. I am certainly not "brand name" oriented when the market is so diverse with options. I have no excuse for my 30 plus BMW m/c years, however. I like 'em. Happy Trails, all you Beemer Folks and be safe. Randy13233

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