Help diagnose top end noise
Results 1 to 6 of 6
Like Tree1Likes
  • 1 Post By J-T

Thread: Help diagnose top end noise

  1. #1
    Junior Member Ecosta777's Avatar
    Join Date
    May 2019
    Location
    MA
    Posts
    23

    Help diagnose top end noise

    Just fired up my 78 cb400A for the first time since I bought it and have been rebuilding it. I haven't done any work to the engine, only mostly cosmetic and mechanical stuff like cables and brakes etc... Also rebuilt the carb.

    It runs fine but still needs to be tuned. I did however notice this disturbing clunking noise on the top end at lower throttle speeds. I'm afraid I'm going to have to rebuild the top end just by the sound. But can anyone help me by trying to pin point it? Sounds more like rocker or valve noise than piston noise, seems to be right under the rocker cover.

    Can't seem to upload the video from my phone here so I've attached a YouTube link of it. (Which hopefully works)
    Thanks
    Eric



    Sent from my Pixel 2 using Tapatalk

  2. #2
    Senior Member Bill H's Avatar
    Join Date
    Aug 2015
    Location
    Waverly Ohio USA
    Posts
    1,062
    You might try adjusting the timing chain and or the valves . The As not that hard to work on and you can rebuild the top end without removing the motor.

    You will need a FSM. If you remove the valve cover I find it helps to move the coils out of the way. Just a thought.

    Bill

  3. #3
    Super Moderator J-T's Avatar
    Join Date
    Jun 2009
    Location
    Tea, South Dakota
    Posts
    9,285
    Valves and chain need adjusting anyway. The sound appears to be absent at idle, only there when throttle is opened slightly. Sound might be an exhaust leak, check the header gaskets.
    Bill H likes this.
    JT
    81 CM400T

  4. Remove Advertisements
    HondaTwins.net
    Advertisements
     

  5. #4
    Senior Member mike in idaho's Avatar
    Join Date
    Jan 2012
    Posts
    2,363
    Are you sure it's in the top end ? right at the end when the motor shuts down you can hear what sounds like the starter coming to a halt.
    '65 YG1
    '65 CB160
    '66 CL160
    '67 CL77
    '68 TR6
    '69 T100R
    '69 T120R
    '72 Commando 750
    '78 XS650E
    '79 Gl1000
    '81 440 LTD
    My company car is a Kenworth

  6. #5
    Senior Member TOOLS1's Avatar
    Join Date
    Dec 2010
    Location
    Kansas City, MO
    Posts
    2,079
    That sure sounds like an exhaust popping to me. I think you need to revisit your carb rebuild.
    TOOLS

  7. #6
    Junior Member Ecosta777's Avatar
    Join Date
    May 2019
    Location
    MA
    Posts
    23
    It is difficult to tell in the video, but it is absolutely coming from inside the valve cover.

Sponsored Links

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •