Honda shaft drive oil leak

Discussion in 'Motorbike Technical Discussion' started by Andrew Szafran, Apr 15, 2005.

  1. I have a Honda CB550SC Nighthawk. Yesterday, after a ride of about 300
    miles at speeds between 70-90 mph, I noticed a bit of oil around the
    final drive breather cap (silver cap on top of the bevel drive unit).
    The oil level is fine - to the bottom of the filler cap threads - and
    the oil is the correct grade of Castrol gear oil. I haven't drained or
    filled the drive since last summer, and have since put about 5000 miles
    on the bike. Should I be worried, or is this what the breather cap is
    there for (getting rid of excess oil so seals don't blow)? Maybe the
    fast ride caused the oil to get a bit hotter than normal and leak?

    The ring gear in the final drive looks fine and the oil seems to be free
    of metal particles. I don't think that the final drive could be filling
    with engine oil due to a blown seal, since, unlike in old BMWs, the
    shaft housing is "dry" not oil-filled, so there's an air space
    separating the two components.

    Andrew Szafran, Apr 15, 2005
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  2. so seals don't blow)?

    No, a breather cap allows whatever container it's installed on to
    *equalize internal pressure* with ambient air pressure. If you
    overfilled the final drive gear unit with oil, some oil might be pushed
    out by excess pressure, or by climbing to a higher altitude.
    Trapped air has to go somewhere. It would push excess oil out of the
    unit, but you're supposed to be aware of the capacity of the unit and
    not overfill it...

    And, the spinning of the ring gear might be throwing a bit of oil up
    inside the case and air pressure changes might carry a few drops of oil
    out of the case through the breather...

    I remember one guy who installed a simple chain oiling system on his
    handlebar and filled it up in the San Francisco bay area. He was
    absolutely amazed that the oiler puked all of its contents all over his
    rear wheel when he rode over a high mountain pass on his Seymour Rhodes
    Tour to Death Valley. Air pressure differences caused that oily mess...
    You could do some research on the boiling point of various lube oils
    and weight of gear oil, or you could just accept the fact that
    mechanical items need to breathe and sometimes the air moving through
    the breather carries a little oil mist with it and that unsightly gooey
    stuff will deposit itself when it cools off...

    Forty years ago, cars had oil filler breather caps on their valve
    covers. The cap was a handy size that fit in your hand, and the cap had
    some wire mesh screen inside it, since there was room for the screen...

    It was a de-mister cap, as well as a breather and an oil filler cap.
    Car engines also had a road draft tube with a tapered end going down
    behind the engine. The tapered end would cause turbulence behind the
    tube and air would be sucked into the engine through the breather/oil
    filler/demister cap when the car was moving...

    (Hey, there's an idea! Maybe you could get some copper tubing from
    your local hardware store and bent it in a curve so the oil drops got
    sucked out and fell onto the highway. And other bikers would ask what
    that funny tube was and you could explain how road draft tubes worked
    and they'd ask, "Are *you* that krusty kritter dude that goes on and on
    about carburetors on")

    But when the engine was shut off and it was still hot, oil vapors would
    rise up to the breather/oil filler/demister cap and the wire mesh was
    supposed to condense the oil vapors back to liquid and the liquid oil
    was supposed to flow back to the engine...

    In prectice though, you'd see some liquid oil on top of your engine's
    valve cover. And oil that condensed in the cap would turn to sludge and
    that sludge would block the desired flow of air through the engine and
    out the road draft tube and you'd start seeing valve cover oil leaks,
    and the oil would run down onto the exhaust manifolds of some engines
    and even cause oil fires under the hood of the car on a really hot

    Been there, seen all that, had an oil fire too. What a mess...

    There's very little room for any demister mesh inside that little
    chrome breather cap on your final drive unit. It may seem unpleasant
    and unesthetic for a little oil to appear there after a long fast ride,
    but what the heck, it's just a little breather cap...

    (Maybe you could get one of the bigger 1.5 inch diameter K&N oil
    breather caps made of fabric and wire mesh and mount that in place of
    the stock breather cap. And when other bikers saw that, you could say,
    "Oh, yeah. Well, I *raced* my Honda at Bonneville salt flats last week,
    and the gearbox got really, really hot as I was going 200 miles per
    hour, so it needed a really big breather filter...")

    Or, you could just leave the little chrome doodad on there and wipe the
    oil off occasionally...
    krusty kritter, Apr 15, 2005
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  3. As I already mentioned, this bike is not like a BMW where the whole
    shaft housing is filled with oil. The shaft housing is dry, and the
    shaft splines and u-joint are _greased_ with molybdenum grease to
    lubricate them. I don't think that oil leakage into the drive unit is a
    real concern here.

    Andrew Szafran, Apr 15, 2005
  4. Andrew Szafran

    Paul Elliot Guest

    Ah! Sorry, seem to have missed that point.

    Paul Elliot, Apr 15, 2005
  5. Andrew Szafran

    Charlie Gary Guest

    I've owned a couple of shafty Hondas, and they both did this. It seems to
    be a common thing, and it just got me to wash my ride a little more often.
    Charlie Gary, Apr 15, 2005
  6. Andrew Szafran

    Rayvan Guest

    Known issue. Go to a Honda dealer and buy the upgraded breather. They
    still sell 'em. My '84 CB650SC did this and the new one never had the

    Rayvan, Apr 15, 2005
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