DOHC tapping

Discussion in 'Old's Cool' started by Reista, Jan 30, 2012.

  1. Reista

    Reista Tech turned Mech

    Joined:
    Nov 30, 2011
    Oddometer:
    171
    Location:
    San Antonio, TX
    This relates to my bike build in my signature below: 1982 GS850. It's a DOHC setup and I've got an odd ticking noise that is definitely coming from the valves (used a stethoscope and the origin was obvious) This developed after a particularly hard start on possibly bad gas which was remedied that same day 0.3 miles later. It is not audible over the noise of the engine, and is really only noticeable while idling at 1k rpm, It also was intermittent at first and has a slight interval to it now still. I'm here to get some info and opinions from the lovely people here after searching the depths of google myself:

    1: Do you think a flush would cure the problem? Even at the risk of taking out other deposits on a 44k engine with no history?

    2: I'm using 10-40w (as manual and cap calls for) fully synthetic oil- could this have caused the issue?

    3: My petcock malfunctioned (I botched a repair, it's fixed now) and was constantly on for a few days. My carbs have overflow spouts. Would there have been any effect?

    4. I filled my oil incorrectly putting about 1.5 qts too much in (had it on it's stand when i'm not supposed to and ran it and topped) this caused oil to come out of the overflow line in the valve cover into the airbox (so that's what that was!) Would this have possibly caused it?

    5. Am I asking the impossible of you guys to help me out on this? :baldy

    Here are some videos I took but 10 minutes ago:

    Bad operating noise:
    <iframe width="560" height="315" src="http://www.youtube.com/embed/I-1nMuNuQ5c" frameborder="0" allowfullscreen></iframe>
    Normal operating noise:
    <iframe width="560" height="315" src="http://www.youtube.com/embed/iqyXP-mcYvo" frameborder="0" allowfullscreen></iframe>

    The tapping has a sweet spot in idle rpms- It's exactly what they manual calls for too. Increasing idle rpms lessens or eliminates tapping but then it's not to spec!

    Am I just being paranoid?
    #1
  2. milkman6453

    milkman6453 Adventurer

    Joined:
    Apr 2, 2011
    Oddometer:
    17
    valve adjustment fixed my tapping noises in my thumper
    #2
  3. Box'a'bits

    Box'a'bits In need of repair Supporter

    Joined:
    Sep 26, 2008
    Oddometer:
    4,298
    Location:
    Wellington, New Zealand
    When was the last time that the carbs were balanced? That's a rough idle. You may find that noise goes away when the bike is running sweetly.
    Has the cam chain ever been replaced? Possibly time for it?

    This definitely isn't supposed to be in some assembly required (its not a build)....Should be in Old School
    #3
  4. aposaric

    aposaric Garden mechanic ;-)

    Joined:
    Jul 6, 2007
    Oddometer:
    270
    Location:
    Zagreb, Croatia
    Try the easy solutions first:

    1. check spark plugs - may be runing on three cylinders

    2. check the valve clearances - may be way out of spec on a 30 year old ;-)

    3. check the cam chain tension - it may be loose or worn, so it can make tapping noise on certain rpm range, and can smooth out if you rev the engine, id depens on the frequency

    3. remove the cam shafts and check for bearings wear, they could also resonate if loose, on different rpm range

    4. you said your petcock was open for few days, you could possibly have had a carb owerflow where the petrol pours out to your combustion chamber ( usualy it is only one, the one that was left with the intake valves open ), so you could have had a "wet start" where you could have coused a hydrolock, alhough it is really rare - it can cause your valves to bend due to the compression of raw petrol in the chamber. I dont want to frighten you, just keep that option as some worst scenario that could happen.

    5. Check all of the components in that order before getting radical ;-)

    5. ofcourse, check your carbs, jets and floats fhile you are at it.

    Don't wory, everything can be fixed ;-)
    #4
  5. Quickv4

    Quickv4 Pro Turd Polisher

    Joined:
    Jul 5, 2009
    Oddometer:
    550
    Location:
    Dickinson, Nort' Dakohtah- Orig. from Wiscowsin
    I agree with all of the above. Remember, the GS's are shim over bucket adjustment, so you will need to find someone who has the tool/shims to adjust if you do find them out of whack.

    I have found carb syncing can get rid of alot of very weird noises.
    #5
  6. G 981

    G 981 Been here awhile

    Joined:
    Sep 7, 2010
    Oddometer:
    738
    Location:
    West of Glaschu
    In the first video clip the tickover was less than 1000 rpm. In the second it sounded higher.
    I think your noise is worse when the engine is lugging at too low revs.
    Balance the carbs and set tickover to the recommended level.
    I don't hear any untoward noise.
    GS cams were known for occasional end float but did not sound like the noise you have.
    #6
  7. TexanInSeattle

    TexanInSeattle Been here awhile

    Joined:
    Dec 2, 2008
    Oddometer:
    326
    Location:
    Somewhere around Barstow on the edge of the desert
    #7