How in the hell did they build them on the assembly line?

Discussion in 'Motorbike Technical Discussion' started by Ted Mittelstaedt, Jun 21, 2006.

  1. Hi All,

    Back in April a bought a 1981 CB750C as a project bike - when I bought it
    it was leaking oil badly (per the seller it was just gushing out of the
    head when the bike
    was running, I never was able to get the bike started) Seller had tried
    using RTV
    (RTV?!?!) on the head to seal it,
    didn't work, just wanted to get rid of the bike, I bought it cheap, etc.

    So, last Friday I happened to be in a bike wrecking yard and asked the
    if he happened to have any CB750 top end parts. To my surprise he had an
    entire 750 engine, sitting there, which he sold me for $100. (30 day
    and he claimed it only had about 20K miles on it, whatever, I wasn't

    So over Saturday I got interested and swapped engines. The wrecking yard
    engine runs really smooth, (better even than my 1980 CB750K) bike has great
    power, idles great, carbs were not all gummed up, life is good, etc.

    What I cannot figure out though, after doing this job, is just how exactly
    the factory BUILT the damn things! That engine took at least 30 minutes of
    jogging around on the jack to get into the frame, I had to turn it at an
    and many bolts had real limited acessibility. And to top it off, getting
    carbs in was horrible. I had decided to keep it as stock as possible and so
    kept the factory airbox - but there's barely enough clearance with the stock
    airbox pulled back to get the carbs in, you have to reach in with long
    and such to get the boots realigned, and there's no way to apply pressure to
    the center of the airbox once the carbs are in that will fully force the
    tubes completely onto the carbs, and the airbox of course bows inwards at
    the center when you try to shove it onto the carbs. It took at least an
    of wiggling it to get it seated, and still the center two cylinders the
    airbox boots
    were not completely on the carbs. And that does not even cover all the
    fishing around to get the airbox tubes and carb draintubes in the right

    I don't suppose that anyone reading worked in the Honda factory on
    the motorcycle assembly line 25 years ago, but I would love to know
    what the tricks were and how they did it.

    Ted Mittelstaedt, Jun 21, 2006
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  2. Ted Mittelstaedt

    dg1261 Guest

    I had two CB750s back in the 70's on which I logged a little over 300,000
    miles. Yes, it was a little like a Chinese puzzle, but twist the engine
    just right and it would slide right in. After a half dozen complete engine
    rebuilds, muscle memory sticks with me like it was yesterday. After
    removing seat, tank, carbs, etc., here was my technique for getting the
    engine out: position a piece of 2x4 on a cinder block to the right side of
    the engine, parallel and about same height as lower frame rail under the
    engine. Place jack under engine for support, and remove all mounting
    bolts/plates except for the long lower rear hanger bolt (just remove the
    nut). Straddle the bike (where seat would be), and with right hand on head
    to wobble engine slightly on the jack, remove long rear hanger bolt with
    left hand. (Engine is now resting on jack and steadied with right hand.)
    Move left hand under head, move right hand under clutch housing. Brace your
    chest against frame backbone (where tank would be), lift engine slightly up
    and rotate forward (head down/rear up) so rear mounting bosses on engine
    clear frame protrusions, slide engine out the right side and rest it on
    right frame rail and the prepositioned 2x4. Unstraddle the bike, left hand
    under rear of engine, right hand under head, lift engine clear of frame.
    Reinstallation was exactly reverse.

    I didn't have the stock airbox on either bike, so had no trouble with the
    dg1261, Jun 21, 2006
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  3. Bwaaahahahaha! Lovely.

    There's a surprise :))


    A lot of older Honda four-cylinder engines go in *much* more easily if
    you remove the oil filter housing and sump first. If the bike has been
    sufficiently stripped, the old dodge is to lay the engine on its side
    on a piece of board or something, and lower the frame over the engine,
    but that's not always possible if you're doing a simple swap with a
    bike that's already built up.

    Fitting carbs back on old fours is a right PITA, agreed. In the past,
    I've used gentle heat (rags soaked in boling water) to soften the inlet
    rubbers. Makes the job easier.
    chateau.murray, Jun 21, 2006
  4. Oh yeah, I forgot to mention that they didn't bother removing the head,
    they just smeared the RTV over the outside of the engine along the
    head gasket seam. Blue RTV.
    I'm just waiting to see what's inside the old engine. Since I never got it
    it could be anything imaginable.
    That's a good idea, I'll have to remember that!

    Ted Mittelstaedt, Jun 22, 2006

  5. I can't imagine anyone trying to seal a head gasket leak by smearing RTV
    on the outside edge, to be honest.....
    The Older Gentleman, Jun 22, 2006
  6. Ted Mittelstaedt

    badaztek Guest

    My uncle used to save his old worn out boots ,to make different gaskets
    seal and even saw him make an bushing once that held til he got done
    with what he needed the equipment for.
    I miss that man he could do just about any repair with an old leather
    boot ,wire and some electrical tape .He was a veteran from WW2 and drove
    a deuce and a half in Germany those guys were amazing what they did in
    the field for repairs we all can learn a thing or two from them.
    badaztek, Jun 25, 2006
  7. Like this: the Wehrmacht had better equipment.
    The Older Gentleman, Jun 25, 2006
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