Dual plugged R65 needs narrow shell plugs

Discussion in 'The Garage' started by jtatknox, Feb 13, 2013.

  1. jtatknox

    jtatknox Adventurer

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    Previous owner had the heads on my '84 R65 machined for dual plugs. The machinist did a really good job and built up the head to allow for .75" reach 14mm plugs. The plugs that were in there were NGK B7ES and easy to remove with a 21 mm socket.

    I bought a new set of plugs and went to install and :huh.... The metal shell hangs up on the nut that holds the head on. Comparing the shells, it seems like the plug that was in there was slightly smaller in diameter. Are the plugs made differently now or did someone turn this plug down on a lathe?

    If the former, would a 5/8" hex plug like an autolite 3922 possibly sneak by the offending nut? I'm having a hard time finding exacts specs for metal shell diameters on various plug types. If not, does anyone know a good place in washington DC to get a handful of spark plugs turned down on a lathe? Obviously I'd prefer to be able to just buy...
    #1
  2. CycleDoc59

    CycleDoc59 Wrench Rider

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    Use a 3/4x14mm plug from NGK or other mfg that has uses a 5/8" socket. The shell diameter is
    a bit smaller. You can grind the diameter down a bit if necessary, no lathe needed. And/or grind a little off the
    head nut edge.....Be sure the plug selected is the correct heat range. Probably not related, but
    regular socket walls can be too thick for motorcycle use. Stamped thin wall sheet-metal plug wrenches
    are often needed to remove M/C plugs, and come in many motorcycle tool kits.
    M/C shops usually have some around out of old bikes.... Also, here's hoping that whomever
    set up the bike knew that dual plugging requires retarded ignition timing.
    #2
  3. greywolf

    greywolf Unpaved road avoider

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    My dual plugged R90S had a 12mm lower plug. I'm surprised a 14mm was added in this case.
    #3
  4. CycleDoc59

    CycleDoc59 Wrench Rider

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    Same here, on an R90S I owned; not really enough space for a 14mm.
    #4
  5. jtatknox

    jtatknox Adventurer

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    I'm not at the timing stage yet, but am aware I need to make some timing adjustments once I get this plug situation fixed. I promise to post some detailed photos of my Accel coil installation.

    I measured the NGK stock plugs with my digital calipers and the shell diameter came out as 19.09 mm. Autolite 63s were somewhat bigger. Anybody willing to measure plugs they may have laying around to see if anything comes in smaller than that (particularly a 5/8 hex option)? Willing to file these down some, but would much rather be able to buy a stock part off the shelf.
    #5
  6. CycleDoc59

    CycleDoc59 Wrench Rider

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    Rubber Chicken Racing has a definitive airhead dual-plugging how-to here:
    http://rubberchickenracinggarage.com/Downloads/TomCutterDualPlugIgnition.pdf

    As you see, 12mm should have been used. But with 10mm plugs available now, they
    would have likely been the best choice. -There is also information there
    to set up timing properly. (The primary function of dual-plugging, as you may know, is
    to allow higher compression without detonation occurring.)
    #6
  7. Plaka

    Plaka Brevis illi vita est

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    Take the nut off. It doesn't do much. originally it was supposed to hold on the rocker cover but it never worked right and the covers leaked. Then the two 10mm nut/stud assemblies were added at the sides. The stud on that central nut frequently strips and I've run for years without that nut, no difference. You can also just take the nut off to install the plug then put it back. Just be real careful tightening it. :-)
    #7
  8. CycleDoc59

    CycleDoc59 Wrench Rider

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    Interesting; you think the second plug is under the rocker cover? It's a head bolt that
    interferes.... You shouldn't skip breakfast or therapy.
    #8
  9. Plaka

    Plaka Brevis illi vita est

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    MMmmm...yes, breakfast. just tell me to STFU.

    I happen to have a pair of Dual plugged R100 heads sitting here, The lower plug is drilled 12 mm. The flat the head nut seats on way deaper than the plug seating surface. Even if I project the plug seating surface outward it goes nowhere near the nut. (I dropped in a nut on a cylinder stud). As I recall the 14mm drilling had an issue with metal getting skimpy between the valves....but I don't always recall well, especially on an empty stomach. Seems my R90 heads had 14mm short reach lowers.

    I would beware turning down the plug body. On the NGK DR5 HS(12mm) I'm looking at the full body diameter is used to bear on the gasket. Same story with a Bosch WR8AP (14mm short reach) and a Bosch WR6DP. You could maybe get a millimeter off the Bosches but that's it.

    If the plug is being inserted in the hole crooked I could see a problem maybe. You could also index the head retaining nut with some shim washers so a flat is presented to the plug (if it isn't already). I'd torque the heads first and see where you are.

    Also, on the NGK I'm lookiing at the plug number are stamped on the metal body of the plug. If the OP's plugs are missing thing this then the plugs may have been machined.
    #9
  10. Plaka

    Plaka Brevis illi vita est

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    MMmmm...yes, breakfast. just tell me to STFU.

    I happen to have a pair of Dual plugged R100 heads sitting here, The lower plug is drilled 12 mm. The flat the head nut seats on way deaper than the plug seating surface. Even if I project the plug seating surface outward it goes nowhere near the nut. (I dropped in a nut on a cylinder stud). As I recall the 14mm drilling had an issue with metal getting skimpy between the valves....but I don't always recall well, especially on an empty stomach. Seems my R90 heads had 14mm short reach lowers.

    I would beware turning down the plug body. On the NGK DR5 HS(12mm) I'm looking at the full body diameter is used to bear on the gasket. Same story with a Bosch WR8AP (14mm short reach) and a Bosch WR6DP. You could maybe get a millimeter off the Bosches but that's it.

    If the plug is being inserted in the hole crooked I could see a problem maybe. You could also index the head retaining nut with some shim washers so a flat is presented to the plug (if it isn't already). I'd torque the heads first and see where you are.
    #10