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256 cam identification question

Discussion in 'The Garage' started by DogBunny, Jul 11, 2018.

  1. DogBunny

    DogBunny Motorcychologist

    Are all 447 cams stamped "447" ?
    So, if you have a cam that does not have the 447 mark, does that mean that it is definitely a 256 cam?
    Or, is there some other way to I.D. a 256 cam?
  2. azman857

    azman857 '80 XS 650SG Rider

    If the cam chain gear is on there are 34 teeth vs the 447's 36.
    robinc likes this.
  3. DogBunny

    DogBunny Motorcychologist

    I was unaware of that.
    The cam in question has a 36 tooth gear. So, even though it is not stamped, like all of the other 447 cams I've seen, it must also be a 447 cam.
    Thank you!
  4. azman857

    azman857 '80 XS 650SG Rider

    I just looked at what I believe to be a 256 cam and there were no stampings anywhere other than timing marks. Stamping marks where it was stamped into general shape and primitive grinding done near the chain ring (both sides) to somewhat smooth it. It is possible to swap chain rings between cams. If it has been done to your stampless cam, maybe someone in it's past has done it for you?
    gggGary likes this.
  5. DogBunny

    DogBunny Motorcychologist

    I hear what you are saying, and yeah, it's perplexing. The cam in question is exactly like you describe, i.e. primitive grinding. The casting looks completely different from several bona fide, 447 stamped cams I have. But that means nothing, it's the grind that matters. Impossible to tell if the gear was changed. I think my next move will be to put a caliper or micrometer on the lobes and compare. I have no idea if that can be done.
    Yamaha sure could have made this a lot easier if they had stamped all of their cams either 256 or 447.
    robinc and gggGary like this.
  6. Yeah, a tough one. Others here who have handled both cams have remarked that it's possible to tell the difference by looking at the lobe widths (duration).

    The by-the-book lobe dimensions are so close, I'm not sure I'd want to rely on those alone, given that a cam may have significant wear. Anyway, here's the book dims.

    256 cam (34 tooth sprocket).

    447 cam (36 tooth sprocket).

    Of note, the XS1 and early XS1B camshafts used an inner roller bearing, instead of the later solid bushing. Somewhere in mid-XS1B is when the roller was replaced by the bushing. Part #3 in this drawing.
  7. DogBunny

    DogBunny Motorcychologist

    Thank you TwoMany. My micrometer is sized for measuring XS650 piston bores and does not go down small enough to measure the lobes, so I used my calipers, but I still am pretty sure that I got accurate enough measurements to definitively say that the cam in question is a 447 based on the specs that you provided.

    And, based on that, I declare that not all 447 cams are stamped "447".

    BTW, and FWIW -- the "tell" when measuring the lobes is dimension "A" on the intake lobe, which is more than a tenth of a millimeter bigger on the 447 cam.
    Last edited: Jul 12, 2018
    TwoManyXS1Bs likes this.

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