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Knock in bottom end on cold start

  • Floyd
    Floyd
    4 years ago
    Hi, Jeff from Perth,  new to hdforums.au, my ride is an '02 Fat boy which I've owned for just over 12mths,  ... Just ridden about 1000ks over last two weekends and have noticed a knock in the bottom end with cold starts.... disappears once warm .... motor not lumpy and no other unusual noise, no change in exhaust, (no blue smoke). Applied screw driver stethoscope all over and knock definitely in bottom end... terrible way to introduce myself but been searching the forum for some clues
  • tussuck
    tussuck
    4 years ago
    Knock or Tap?  Its nt unusual to hear a tappity sound on a cold start as the lifters come up to pressure.  Could be a sign that a lifter might be going out.
  • Floyd
    Floyd
    4 years ago
    Definetly not a tappet tap, it's a knock, I have found similar if not same problem under "big end knock at idle" on the forum... no resolution but good description of same problem.... I will attempt to upload some YOUTUBE footage.
  • imoo6170
    imoo6170
    4 years ago
    May be a loose compensator nut or maybe the primary chain tensioner. There are a lot of mechanically knowledgeable member's here so I am sure someone will chime in with some possibilities
  • speedzter
    speedzter
    4 years ago
    Bottom end knock normally wont go away when warm.
    Possible piston slap, or carbon build up in the head, or even a primary issue.
  • dicko
    dicko
    4 years ago
    Quoting imoo6170 on 27 Jan 2020 07:20 AM

    May be a loose compensator nut or maybe the primary chain tensioner. There are a lot of mechanically knowledgeable member's here so I am sure someone will chime in with some possibilities

    My 2006 road king did this and it was the loose compensator nut.
  • Ken in Cairns
    Ken in Cairns
    4 years ago
    Yep compensator would be my bet too, worn bearings don't come good when warm.
  • markwoumla
    markwoumla
    4 years ago
    You could try and replicate the sound , (if it is compensator or loose compensator nut),,,
    1. Start bike and put into first gear.
    2. Hold front brake lever tight.
    3. With front brake lever tight,, and say 1500 rpm,, Slowly let out clutch lever, (the bike wont move,, but you don't wont to stall either)... Do this a couple of times..

    If you hear banging and clanking ,, it is a sign you compensator may be failing...
    If you have a loose compensator nut , you would have some banging and clanking , but this noise would not normally stop when engine is warm/hot...

    Removing primary cover etc,, checking parts etc,, tightening everything to spec etc,, is really the only way to take the primary area out of the equation...

  • Floyd
    Floyd
    4 years ago
    All responses much appreciated, I will investigate the compensator issue and see if it is resolved... I will report back so if anyone else needs the same query answered.
    Cheers. 
  • Grease Monkey
    Grease Monkey
    4 years ago
    Quoting speedzter on 27 Jan 2020 08:29 AM

    Bottom end knock normally wont go away when warm.
    Possible piston slap, or carbon build up in the head, or even a primary issue.

    Carbon could be it , piston banging the head till it warms up, bit of seafoam or that Subaru top end cleaner would sort it if it is.
  • paulybronco
    paulybronco
    4 years ago
    Quoting speedzter on 27 Jan 2020 08:29 AM

    Bottom end knock normally wont go away when warm.
    Possible piston slap, or carbon build up in the head, or even a primary issue.

    Quoting Grease Monkey on 28 Jan 2020 07:23 AM

    Carbon could be it , piston banging the head till it warms up, bit of seafoam or that Subaru top end cleaner would sort it if it is.

    And then drop the oil Hilly?
  • Floyd
    Floyd
    3 years ago
    Follow up on this bottom end knock....
    I put the bike into the shop...... investigation ..... got the bike back, problem all fixed.... it was the compensator! Mechanic believed that one of the washers was missing... not sure how that could develop but was obviously pulled apart and put back together and noise gone ... so 10 000ks later still all good... a bit of a mystery .... 
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