Seeking opinions on noise 78 R100

Discussion in 'Airheads' started by garyinalt, Nov 14, 2011.

  1. garyinalt

    garyinalt Adventurer

    Joined:
    Aug 20, 2008
    Oddometer:
    83
    Location:
    Woodstock, GA
    I have a noise coming from what I think is just the left cylinder. It is a tapping sound only from 3000 to 3200 rpm. No other symptoms anywhere else on the rpm band. I checked my plug and it has black soot as opposed to the right side which is a nice grey. The top of the piston has a soft coating of black stuff which I can remove with a screw driver inserted. I have checked rocker end play and valves and they are spot on. The bike has just 15k on it and no valve recession just yet. The only thing that just might be coincidental is that 500 miles ago I added 1/2 gallon of aviation fuel for its lead content. Any ideas before I start tearing into this?
    #1
  2. 97oilhead

    97oilhead Been here awhile

    Joined:
    Mar 5, 2008
    Oddometer:
    189
    Location:
    Southern Ontario, Canada
    Have you checked to see if there is anything loose and vibrating on the frame or engine?

    I know that my 100's seem to vibrate the most when they are in the 3000-3200 range.
    #2
  3. garyinalt

    garyinalt Adventurer

    Joined:
    Aug 20, 2008
    Oddometer:
    83
    Location:
    Woodstock, GA
    Mine vibrates there too but this almost sounds like the valve making the noise. I plan on taking it apart to inspect/clean the head. Then I will run it again to see if it made a difference.
    #3
  4. danedg

    danedg Horizontally Opposed

    Joined:
    May 13, 2008
    Oddometer:
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    Location:
    U-puku-ipi-sing
    Make sure your sparkplug wires and caps and stuff are nice and tight. The difference in plugs indicates either a carb or spark problem, as in, it's not firing correctly, if at all. Throw fresh plugs in...Light grey is almost too hot...black is fouling. You're looking for something in between on both sides.
    #4
  5. garyinalt

    garyinalt Adventurer

    Joined:
    Aug 20, 2008
    Oddometer:
    83
    Location:
    Woodstock, GA
    In case anyone is still interested in the noise problem, its been resolved. I removed the head off the left cylinder and found the reason that one had soft carbon on the top of the piston. That is the side that has the crankcase pressure relief valve that allows the oil to be reburned. I cleaned it and decarbonized the head and put it back together. Then on a slow ride at around 3000 rpm the clacking noise returned. I bent over to try and hear it a little better and then I saw the horn shaking wildly. That was the noise! Once I removed the broken horn, problem solved! Wish I would have checked that first and save me all the trouble. Live and learn.
    #5
  6. Wirespokes

    Wirespokes Beemerholics Anonymous

    Joined:
    Jul 26, 2002
    Oddometer:
    8,725
    Location:
    Jackson's Bottom Oregon
    LOL :rofl

    Glad you found it and was so easily handled. :lol3

    I had an old Volvo that would make a buzzing/vibration at certain RPMs. I couldn't find it no matter how hard I looked and since it didn't seem to affect running, just lived with it. Many thousands of miles and a few years later I discovered that the Intake Plenum brace at the block end attachment was missing its bolt! Problem solved.
    #6