675.cc • Triumph 675 Forum

Mystery knocking noise

Discussion in 'Maintenance & Tweaks' started by Nik, Jan 11, 2025.

  1. Nik

    Nik

    Thread Starter

    290
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    Location: Holland
    Hi folks,put a 2202 765 Peter Hickman Racing tunes engine in my race bike and when I was done and went to start it for the first time I was turning it over on the starter motor for a while and it didnt fire up,I was not expecting to as there was no fuel in the hoses/injectors.As the battery power began to fade the engine started making a very nasty knocking noise.I stop trying to start it as i didnt want to damage anything.
    The guy i bought the engine from was really suprised by my my problem as it worked fine when he took out of his bike and its only been used for 3 trackdays since a full rebuild.Which is why I bought it.
    Drained the oil and that was clean.Took the engine out and checked camchain and tensioner,cams and shim buckets and valve springs all good.Took the head off and everyting was good.Turned the engine over by hand and couldnt feel anything unusual.
    Could the problem be starter motor related??
    Any other ideas??
    Cheers Nik
     
  2. Trogdor

    Trogdor

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    Location: UK
    If the engine spins by hand without issue then that's a good sign. I know that a ruined sprag clutch will just spin without engaging the flywheel, but also can make a knocking noise as it is slipping (too much). It's common on big twins but can probably happen on 675 or 765s. Might be worth checking if engine is out.
     
  3. Nik

    Nik

    Thread Starter

    290
    81
    28
    Location: Holland
    Thanks for your thoughts Trogdor.
    If I turn the engine by hand while paying attention to the generator fly wheel I should see this not turning ?? Or something like that??
    I’ll have a look for sure.
     
  4. Trogdor

    Trogdor

    48
    15
    8
    Location: UK
    I'm not sure you would see it when turning by hand, as I don't think the torque and velocity would be high enough.

    An engine expert might have better ideas, but my last Ducati would destroy sprag clutches when it struggled to start. This would result in the starter just spinning (not the flywheel) and then with occasional clunking. Starting the bike without firing up produces wear on one-way sprag clutch, but they could also be broken.

    I'd just check since you are in there.
     

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