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Rythmic knock from top end.

Discussion in 'XJ Technical Chat' started by fatnfast, Jul 3, 2014.

  1. fatnfast

    fatnfast Member

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    My XJ550 has a quiet knocking sound from the top end.
    I used a stethoscope and narrowed it down to what I thought was the tacho drive. I removed the cable, but this made no difference, so I removed the tacho drive and it all looks fine, no damage, no leaks.
    Next I removed the cam cover, cams are perfect, plenty of oil is getting to them. The cam chain is tensioned fine as well.
    I know its difficult to diagnose a noise on the forum, but maybe someone has come across this before.
    Its not loud at all and best described as a rhythmic knock, knock, knock, pause, knock, knock, knock.
    It disappears as the revs increase above 2k (or could be just drowned out by the engine noise).
    I seem to recall many years ago that there was an issue with cam end float and mine is a very early model, although I have no idea if it can be left alone or must be dealt with.
    The bike starts on the button and runs great. Valve clearances all done, carbs balanced etc.
     
  2. fatnfast

    fatnfast Member

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    Found the info on cam end float which matches my issues. I will measure the end float in due course to confirm.
    [​IMG]
     
  3. a100man

    a100man Well-Known Member

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    'If clearance exceeds specification replace...'

    replace what ?? The suspense is palpable..

    Best

    JS
     
  4. fatnfast

    fatnfast Member

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    Ha, ha! Just a better machined camshaft cap. Yamaha says it does not effect the adversely affect the engine and was basically corrected if the customer complained.
     
  5. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    You sure it's from the top end and not the 550's characteristic primary chain flop at idle?

    The cam clearance thing results in more of a tick or "tap" than a knock.
     
  6. wizard

    wizard Active Member

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    Don't forget the exhaust port leak, makes a knocking sound.
     
  7. fatnfast

    fatnfast Member

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    Thanks Fitz and Wizard. Definately not an exhaust leak, but I did double check anyway.
    Without doubt it is from the top end and the loudest point is from the tacho drive area. Cam chain tunnel is very quiet, so I think I can rule that out. The bottom end is extreamly quiet, no knocks, taps or rattles at all.
    As I said it is always difficult to diagnose from a 'noise' description on a forum and Im sure my knock would be somebody elses tap!
    It may sound silly (well very silly), but the closest sound I can replicate would be clicking your tonuge on the roof of your mouth. It reduces as the revs increase and is gone by 2k.
    The Yamaha cam shaft side play seems to fit the bill, but I will check the play in due course. At the moment I'm just enjoying riding it :) .
     

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