Swapping cyl.head and not the cams...

Discussion in 'Motorbike Technical Discussion' started by Paul Barrett, Dec 1, 2008.

  1. Paul Barrett

    Paul Barrett Guest

    This is on a 1980 CB750 DOHC...
    I had an upper timing chain break, resulting in 2 bent valves and worse, 2
    broken valve guides.
    Rather than trying to swap valve guides, I picked up a cylinder head from
    the same year model really cheap. It has the cam bearing caps, but not the
    cams or the shim buckets.
    So my question...
    How bad is it to use the old cam and shim buckets in a different head?
    Must this be machined to match? Should I plastigauge it?
    Paul Barrett, Dec 1, 2008
    1. Advertisements

  2. You'll be fine. It's the cam bearings that are matched to the head.
    Otherwise, if you think about it, you'd never be able to replace a
    camshaft without changing the head as well, which would have put
    Yoshimura and others out of business decades ago.
    The Older Gentleman, Dec 1, 2008
    1. Advertisements

  3. Paul Barrett

    . Guest

    Plastiguage is a crushable plastic fiber which is typically used to
    approximate how much clearance there is between the crankshaft and the
    main and rod bearings.

    Plastiguage is an inexpensive substitute for precision micrometers.
    The home mechanic can determine whether he needs over-sized bearing
    inserts or if the crankshaft is badly worn without buying the expen

    As I recall, the original Kawasaki Z-1 engine had removable cam
    bearing inserts.

    However, modern Japanese overhead cam engines don't have bearing
    in the head, they run the camshaft directly in the aluminum head and
    if the
    head is damaged you would have to replace it, unless you can find a
    really good motorcycle machine shop that knows how to line bore the
    bearing caps and head.

    In any case, you need the factory shop manual to find out what the
    dimensions of the cam bearings and lobes should be and then you need
    to use a bit of judgement if the parts are worn a thousandth of an
    inch or some more than the manual limit.
    ., Dec 1, 2008
  4. Paul Barrett

    TOG@Toil Guest


    In other words, you have not answered the question. So you don't
    actually know what you are talking about. On a great many Jap bikes,
    the cam caps are matched to the head, like I said.

    Oh, and some modern Japanese bikes use roller bearings in their heads
    as well.

    If the head and cam bearing caps are in fine condition, and ditto the
    replacement cams, then all the OP needs to do is to bolt in the
    replacement cams and ride away.

    If any or all of the cam caps and head bearings surfaces are buggered,
    then obviously he'd need to do a whole load of work, but the fact that
    he's trying simply to avoid replacing two valve guides (not in itself
    a tough job, but one for a specialist) would suggest that there's
    nothing wrong with the used head he's bought. And if the camshafts he
    wants to put in it were buggered also, I don't think he'd be shoving
    them back in his bike.

    Barrett - like I said, just put the cams into the used head, and bolt
    that onto the block.
    TOG@Toil, Dec 1, 2008
  5. Paul Barrett

    . Guest

    First generation Honda pile-of-craps had roller bearings on the ends
    of the cams.

    But name just *one* Japanese design from the middle 1970's and up that
    has *roller bearings* in the head.

    If you can be bothered to support your incessant *quibbling*, that is.
    ., Dec 1, 2008
  6. Paul Barrett

    TOG@Toil Guest

    Kawasaki ZX7R. Kawasaki ZX9R. Both do, at the camchain drive end.
    Possibly others as well, and I cba to check right now, but those two
    do for certain, and I know, because I've worked on 'em. Which,
    evidently, is more than you have.

    Plain bearings elsewhere, but nonetheless roller bearings they use.

    Are we feeling stupid now? :)
    TOG@Toil, Dec 1, 2008
  7. Paul Barrett

    Bob Scott Guest

    That sounds about right - when I blew up my first CB900 (long stroke
    version of the same engine) we used the inlet camshaft & buckets from
    one engine & exhaust cam from another.

    It went fine until it suffered an ignition failure and I replaced it
    with a cheap VFR...
    Bob Scott, Dec 1, 2008
  8. Paul Barrett

    TOG@Toil Guest

    Oh, and as you're so fond of posting fiches, here you go:


    You can clearly see the ball races at the end, by the cam sprockets.
    TOG@Toil, Dec 1, 2008
  9. Whatever got you so worked up that you actually looked something up to
    a useless argument?

    What does this have to do with a 1980 CB750, anyway?
    Horst Weltschmerz, Dec 1, 2008
  10. Bwaaahahahahaha! Look at the timing of the postings. I'd already told
    you the truth, before I even bothered to look this up.

    In other words, I didn't look it up because I needed to "win an
    argument". I already knew it. I gave you the link for your benefit,
    because I'm a nice chap.

    And why did I state it? Because you, *once again*, paraded your complete
    lack of knowledge in a technical ng and your ignorance warranted

    Bwaaaahahahahaha! You utter, utter *loser*. You give the OP a load of
    irrelevant waffle, it's corrected for what it is, you start jumping up
    and down and screaming, demand proof of what I said, and it's

    ....and then you ask a question like this?

    The Older Gentleman, Dec 1, 2008
  11. Paul Barrett

    Pip Luscher Guest

    If we include all bearings containing rolling components, SR500 and
    (probably) derivatives had a camshaft supported in ballraces. Or are
    we restricting this to rollers?
    Pip Luscher, Dec 2, 2008
  12. Paul Barrett

    . Guest

    *Who cares*? What will be gained by playing The Old Gasbag's game?

    The original poster had a question about a 1980 CB750 DOHC, but the
    Old Gasbag just had to trash the thread with exceptions and ridiculous

    Like he always does...
    ., Dec 3, 2008
  13. Well, I was taking ball races to mean 'rollers' in this conext, as
    opposed to plain bearings, and having owned an SR500 I know what you say
    is true. And the XS650 used them as well, but Krusty *did* say "just
    *one* Japanese design from the middle 1970's and up", so I deliberately
    didn't name them.
    The Older Gentleman, Dec 3, 2008
  14. You do, remember? You got all shouty and issued a challenge and...

    It was taken up.

    And now you're getting even more petulant because you've been made to
    look an idiot. Which, it has to be said, happens frequently.

    I mean: "Lighter vehicles are sprung more rigidly than touring sedans".
    What a load of bollocks.
    He did. Which I answered succinctly and correctly, and which you didn't.

    What's your next point?
    The Older Gentleman, Dec 3, 2008
  15. Paul Barrett

    . Guest

    My point is that you were an exceptional child, bored with your school
    work and always seeking alternative amusement or demanding attention
    from the beleaguered teacher.

    Nowadays that would be called "attention deficit disorder", or ADD.

    And you grew up to be an exceptional adult, a pain-in-the-ass who is
    always looking for a tedious exception to every generality just to
    draw attention to himself.

    Adult Attention Deficit Disorder...

    I suppose we will now see this thread mushroom out to fifty or a
    useless messages, instead of dying from disinterest.

    Why couldn't you just have a passion for philately combined with Zen?

    You needn't answer that rhetorical question.
    ., Dec 3, 2008
  16. Paul Barrett

    TOG@Toil Guest



    Do you see what a complete arse you are making of yourself? Obviously
    not, so:

    1. OP asked a decent tech question.

    2. I provided a decent tech answer, which was entirely correct and was
    later substantiated by another poster, from personal experience.

    3. You posted reams of irrelevant waffle and didn't answer the
    question at all.

    4. I pointed out the irrelevance of your reply, added a very brief
    throwaway line about camshafts, and reiterated my advice to the OP.

    5. You jumped down my throat, wittering on about 1960s Hondas, and
    demanding evidence of a 'modern bike' using the sort of cam bearings I
    carelessly mentioned.

    6. Said evidence was provided.

    7. To try and cover your imbecility and ignorance, you then started
    squealing that this was irrelevant to the OP's bike, conveniently
    ignoring the fact that (a) you had issued the challenge in the first
    place and (b) that the OP's bike question had been settled right at
    the start of the thread.

    8. And now you accuse me again of causing the thread to divert from
    the OP's question. See (7) above.

    You are a sad, sad, frustrated, hate-filled, warped, perverted,
    ignorant, stupid little waste of spermatazoa. Sorry, but it has to be
    said :)
    TOG@Toil, Dec 3, 2008
  17. Paul Barrett

    . Guest

    Oh, and while the king was looking down,
    The jester stole his thorny crown.
    The courtroom was adjourned;
    No verdict was returned.
    And while Lennon read a book on Marx,
    The quartet practiced in the park,
    And we sang dirges in the dark
    The day the music died.
    99.9999999% of all spermatzoons fail to perform their task, but the
    world was cursed with The Old Gasbag.
    Take your soap box to Speakers Corner and rave at the crowd.
    ., Dec 3, 2008
  18. Paul Barrett

    TOG@Toil Guest


    And again, the last resort: childish insults. You really need a better
    scriptwriter <G>.
    TOG@Toil, Dec 3, 2008
  19. Paul Barrett

    Pip Luscher Guest

    Ah. In retrospect, I replied to the wrong person. It made sense at the
    time, honest.
    Pip Luscher, Dec 5, 2008
  20. Paul Barrett

    . Guest

    Next time you see TOG humping somebody's leg, just remember what
    Randy Quaid told Chevy Chase.

    "It's best to just let him finish what he's doing."
    ., Dec 5, 2008
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.