Simian's ZX7R (longish)

Discussion in 'UK Motorcycles' started by The Older Gentleman, Sep 13, 2003.

  1. Simian's up to his arse in alligators atm, but I daresay he'll be
    posting more pix in due course.

    It now looks certain that the ball race supporting the inlet cam, at the
    drive end, failed, and this took the cam with it. It's possible that the
    cam snapped at the race, and took the ball race with it, but my money's
    on the race going first. Either way, that caused the blow-up.

    The question is: why?

    To recap - we measured it, shimmed it, and torqued the cam cap down to
    exactly the right specified torque, tightening all the (20!) bolts in
    the correct sequence. Put in the camchain tensioner unit, after first
    pushing the plunger back into it, as per manual. Turned the engine over
    a few times to check everything was OK, and that was it. 50 miles later,
    while it was being given max welly in fourth, it let go.

    This worried the feck out of me because I was *certain* we'd done
    everything right, but coming so soon after a re-shim, it was suspicious.
    The cam timing was right - or it wouldn't have run at all - and there's
    no way we over-torqued the cam cap. I even checked that the torque
    settings in the Haynes BoL were correct (I've known them to be wrong
    before) and they were. And if it was *that* over-tightened I'd have
    expected to have stripped a cam cap bolt, or broken the cam cap itself.

    So..... possible over-tightened camchain, despite doing everything by
    the book? Unlikely, and Simian tested the chain tension with his finger
    before we popped the cam cover back on, but still....

    When Simian removed the tensioner after the blow-up, it was nearly fully
    extended, but then as the cam snapped and the sprocket went flapping
    around, that would have put a load of extra slack in the chain, so you'd
    expect that. And anyway, an over-tightened chain would probably take out
    the exhaust cam first, since that's the one that gets most of the drive
    loading. And that's if it hadn't smashed the camchain tensioner system

    Last port of call was the tensioner blades. If the chain had been under
    serious over-tension for 50 miles, you'd expect to see signs of heavy
    wear on the composite surface. Apparently they look perfect. So it
    wasn't the tensioner.

    It now looks as if a flaw in either cam or ball race was to blame. Maybe
    a casting flaw in the cam, maybe a small flaw in the race, and as Simian
    says, just shifting them to do the shims was enough to upset them.
    Sounds ferkin' unlikely, but I remember when the main bearing race of my
    RD350 failed - sitting at traffic lights and all of a sudden the engine
    went from a pleasant burble to a horrible grinding. The inner race just
    chose that moment to fail.

    As someone (no names) here said in an email, Simian has been very calm
    and cool about all this. If I'd dropped my bike into a dealer for a
    re-shim and it went pop afterwards, I don't think I'd be happy. And yes,
    some form of "arrangement" was offered if it turned out that (having
    eliminated all the other likely causes) it turned out that the camchain
    tensioning was to blame.

    If anyone's got any alternative explanations, please air them, because
    (and yeah, with a certain amount of relief), I've worked it down to the
    above. Shit happened.

    Anyway, I've got the replacement lump in the back of the motor and am
    about to trundle it round to Simian's gaff, because I'm going that way
    anyway (big sale at Thorne's, the bee equipment place in Windsor). It
    looks like a bargain engine, too.
    The Older Gentleman, Sep 13, 2003
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  2. The Older Gentleman

    Alan.T.Gower Guest


    Isn't it always the same, if it's going to go wrong it's when you do a
    favour for a mate.

    This is one of the reason why I would never sell a computer to family or
    friends [1].

    [1] I usually ended up giving them away with a don't call me disclaimer.
    Alan.T.Gower, Sep 13, 2003
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  3. The Older Gentleman

    Martian Guest


    Were they new races?
    Martian, Sep 13, 2003
  4. The Older Gentleman

    Cane Guest


    cane [at] ¦ fireblade, r30
    botafo t#50 f#03 YTC #15 bbb #6 pm #6 apostle [kotl]
    "What was your crime Spazpecker?"
    Cane, Sep 13, 2003
  5. The Older Gentleman

    flashgorman Guest

    Big Kwacks always have trouble with races, look at their Motogp bike.
    flashgorman, Sep 13, 2003
  6. The Older Gentleman wrote:


    In all honesty when you pull an engine down to do a service all shit can
    break loose. You don't know the history of the engine. You don't know
    what previous ham fisted grease monkey has clubbed the cam into place or
    sent is flying across the workshop floor missing the apprentice by

    The ball bearing on the end could be simply knackered because the
    contents of the apprentices nose and the grease monkeys fag ash ended up
    in the bearing along with the contents of the sand pit.

    That and the fact that the head was left off while apprentice 2
    accidentally steam cleaned the bike and apprentice 3 was using the angle
    grinder on the exhaust studs on the bike next to it.

    So in reality what I'm trying to say is, If the job was done to the
    book, and you had no difficulties while doing the job all should be
    well. It looks like the cam chain was at correct adjustment this time.
    It could have been over tight last time. So when you did the service it
    disturbed the bearing (which was already knackered by the sound of it)
    enough to make it fail. This would be the same scenario even if I or a
    shop did the job. If its going to go splat it will go splat. It's no
    good trying to analyze what you did wrong, because you probably did
    nothing wrong...

    So pick yourself up, take a long drink, and put it down to

    [1] I did a head gasket on a RD400. The bloke then said I'd made his
    clutch slip. I took it apart and found a knackered RD350 clutch in it. I
    asked him what shop he had it serviced in. The shop had a history of
    this sort of thing happening. He got a new clutch because one of the
    grease monkeys swapped it over. Brother had fisty cuffs with one grease
    monkey who didn't realise there was a circlip holding the fork seals in
    on his CB550 fork leg. Bro had a new fork leg lower from the shop. The
    old one had had the top chiseled off. I did the tappets on a Kawasaki
    GPX1000. One of the rockers snapped when I was undoing it for gods sake.
    It bounced of the roof of the garage. Another grease monkey had heated
    the head/barell stud up so much on a CB750 that the alluminuim melted
    where it went into the crankcase. The stud was at 5 degrees to true. God
    knows what happened to that bike. I could go for ever.

    SimonB - South Wales. BOF#32
    Triumph Sprint ST,
    ZXR750L2 Wazimbaki.
    Kawasaki Z1R For Sale
    eric the brave, Sep 13, 2003
  7. You can normally tell if a ball race is worn out. But not wit hal lthe
    other racket going on in the cylinder head. The failure is normally the
    cage holding the balls apart...

    SimonB - South Wales. BOF#32
    Triumph Sprint ST,
    ZXR750L2 Wazimbaki.
    Kawasaki Z1R For Sale
    eric the brave, Sep 13, 2003
  8. The Older Gentleman

    Martian Guest

    no reason, just wondering.
    Martian, Sep 14, 2003
  9. The Older Gentleman

    Simian Guest

    The Older Gentleman :
    Only if I manage to get the lower engine mounting bolt out. Bastard
    thing is locked solid - the nut came off easily enough but the bolt
    will not budge.

    The neighbors are having a tea party in their garden at the moment
    so I've given up for now (don't think they'd appreciate the sound of
    power tools).
    Cheers for that. Looks like the bike it came out of had been serviced
    recently as well.
    Simian, Sep 14, 2003
  10. The Older Gentleman

    Simian Guest

    The Older Gentleman :
    Right, how the **** do you get stuck engine bolts out?

    I think the fucker is bent or something; the nut came off, and I've managed
    to move it about half an inch, but it just won't go any further. It'll turn,
    a little reluctantly, but won't come out.
    Simian, Sep 14, 2003
  11. The Older Gentleman

    Pip Guest

    Stupid, I know - but this is the mounting bolt that holds the engine
    in the frame, right? You _have_ taken the weight off the mounting,
    using a trolley jack with an interposing piece of wood, haven't you?

    Assuming it isn't the weight of the engine causing stress, I'd turn it
    and keep turning it, applying Plus-Gas or Duck Oil, hoping to lube
    away any corrosion-induced stiction along the way. Once it turns
    freely, it should slip out. Heat is always a possibility, providing
    there's nothing around that will object, but I would assume that
    various rubbery bits may register their disapproval by immolation.

    In desperation, I'd slip the nut back on and thump it with a hefty
    hammer (the nut protects the threads). Check for unsuspected washers
    and circlips first, though.
    Pip, Sep 14, 2003
  12. Whaaa-aat?

    Bent engine bolts?

    A bit unlikely, I'd have thought.
    The Older Gentleman, Sep 14, 2003
  13. The Older Gentleman

    Simian Guest

    Champ :
    You mean the lock nut? Made my self a tool for that out of an old
    A/F socket. You can't properly loosen the spacer until the bolt
    has been removed, can you?

    Hmmm. All of the other bolts have been taken out (and put back in, and
    taken out again) with no problems.
    Simian, Sep 15, 2003
  14. Simian wrote
    Diesel I hope. Kin good penetrating oil diesel is. Get a gallon of
    that in a can, use three drips on the stuck thing and throw the rest in
    for recycling and it will still be cheaper than a can of stuff.
    steve auvache, Sep 15, 2003
  15. Sounds like a job for Mister Blowlamp.
    The Older Gentleman, Sep 15, 2003
  16. The Older Gentleman

    Simian Guest

    The Older Gentleman :
    More violence, heat, bit more violence, heat, swearing, and finally
    reaching for the tungsten carbide drill bits, that my prediction for

    It's a 6-8 inch long bolt, 1/2 open to the elements, right in front
    of the rear wheel - a stunning bit of design, Mr. Kawasaki.

    Still, I've a friend comming round to hit it while I turn it, which
    I think is my best bet.
    Simian, Sep 15, 2003
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