KTM 640 LC4 - Loud clicking noise when idle

Discussion in 'Thumpers' started by ciukes, May 18, 2013.

  1. ciukes

    ciukes ciukes

    Joined:
    Apr 25, 2011
    Oddometer:
    25
    Location:
    London, UK
    End of the story...

    Removing the auto-decomp didn't work for me. The bike wouldn't start no matter what.
    http://www.youtube.com/watch?v=CKAjv24Rjos

    So back to the old setup with auto-decomp on. Sure it's loud on idle but at least it works.

    I cleaned up the camshaft, auto-decomp, oiled generously everything and assembled engine top for the last time. As soon as the top was on I started the engine hoping for a change. Nope... the engine greeted me with good, old click-clacking.
    Oh well... I spent the rest of the afternoon assembling the bike all together.

    Then I started the engine and... surprise! Clean sound with no clicking!
    http://www.youtube.com/watch?v=jjPcquuXynA

    My personal bet is on dirty camshaft and auto-decomp. I guess the previous owner was not much concerned about oil changes so dirty residue build up and stoped auto-decomp from moving freely.
    #21
  2. Syncrosimon

    Syncrosimon Numpty

    Joined:
    Sep 9, 2011
    Oddometer:
    32
    Location:
    Devon, England.
    My LC4 makes that loud clattering when the idle is too low, it does it just above stall speed for the engine. I have had the top end apart at 15,000 miles and only the water pump shaft was worn.
    #22
  3. kg23

    kg23 Adventurer

    Joined:
    Aug 19, 2007
    Oddometer:
    19
    Location:
    San Francisco, California
    I've had the problem (clicking clacking from auto decompression system) from time to time (2000 Duke II) and found it was definitely due to too-low idle speed. I also had it occur when I had mistakenly under-filled the crankcase after an oil change.

    However, after a spirited 500+ mile ride this past weekend, my auto-decompression system is click-clacking quite heavily at an 1800rpm idle and even does it occasionally as high as 3000 rpm.

    If the spring (#45) wore out/broke, would that cause the decompression system to activate more frequently? The diagram isn't really clear on how it works. Assuming my valves are properly adjusted (the sound is definitely not valves), I guess I have to take the cam out to check?

    Attached Files:

    #23
  4. kg23

    kg23 Adventurer

    Joined:
    Aug 19, 2007
    Oddometer:
    19
    Location:
    San Francisco, California
    #24
  5. kg23

    kg23 Adventurer

    Joined:
    Aug 19, 2007
    Oddometer:
    19
    Location:
    San Francisco, California
    So here's my report on my horrible sounding top end (2000 Duke II, 18K+ miles, original owner):
    After a 500 mile weekend ride, the decomp. system was clacking away at idle and the valves sounded terrible. I changed the oil and found a fair amount of metal crap on the magnetic plug. I checked the valves and they were a bit loose. However, the clacking sound was unchanged after all this.

    I took the bike to my local dealer and they called back with the question "Did you ride this thing in?!" Apparently the large cam bearing had eaten itself (#23 in pic above). 2 balls were missing as was most of the cage. This allowed for a bunch of play in the cam that was somehow causing the decompression system to clack away.

    I had them replace the ball bearing (#23) and the needle bearing (#25) and hoped for the best... and got it. Bike is running great. Much quieter top end. I am going to change the oil again in a few hundred miles and check the valves. Dodged a bullet!

    So... something else to check if you have a strange decompression clacking... worn cam bearing(s) and cam play.

    #25
  6. NevBlu

    NevBlu Been here awhile

    Joined:
    Feb 1, 2014
    Oddometer:
    184
    Location:
    Carson City, NV
    We all know that parts wear out so when working on the cam shaft, my opinion is to replace the #45 spring. Very low cost (<$1) for the added benefit to the decompression issue. At a minimum measure it's length and compare to the manual.

    Here is my '01 LC4 640 cam before disassembly. However, my end of the cam shaft is within tolerances, so I will not be replacing the needle bearings. I may post later when it is rebuilt.

    Attached Files:

    #26