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  1. #1
    n00bie


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    Default Z900 Z1000 Cylinder Head Differences

    Does anyone know if there are any differences besides the combustion chamber diameter?

    Regards Gnit
    Z9

  2. #2
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    Default

    sorry Gnit, do not know

  3. #3
    I'm Getting There


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    Default

    all 900's have 6mm exhaust studs, all 1000's 8mm

    if you want to keep it looking original 6mm can be drilled out to 8mm and 8mm can be stepped down to 6mm


    all 900's have square valve stem spring collars, all 1000's have round, keep this in mind if you need new valves as you'll need matching collars
    Last edited by 900FOUR; 25-06-17 at 12:56 AM.

  4. #4
    n00bie On a Mission


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    Default

    Quote Originally Posted by 900FOUR View Post
    all 900's have 6mm exhaust studs, all 1000's 8mm

    if you want to keep it looking original 6mm can be drilled out to 8mm and 8mm can be stepped down to 6mm


    all 900's have square valve stem spring collars, all 1000's have round, keep this in mind if you need new valves as you'll need matching collars
    Valves can vary greatly...depending on which head you want to use..
    I guess there's a reason for bigger or smaller valves..??

    WHY?.

  5. #5
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    Default

    Thanks all

    An acquaintance has a Z1000-A2 which has run out of meat around one of the valve seats.
    I now know that the 8mm exhaust studs along with more material cast around them are specific to Z1000A1/A2, '78 Z1R (although black) and the US LTD of the same era.

    If anyone has one for sale let me know.

    Regards
    Z9

  6. #6
    I'm Getting There


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    unless l read your post wrong, surely a good engineering shop can weld this area up?

    cracks between the plug holes and the plug hole itself (common) l've had welded up, even without removing the seat.

  7. #7
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    Default

    yep I have had valve seats replaced. They mill out the old one, machine a new seat to fit, then it's back to cutting a new valve seat in the new material. Manuals will tell you the finished valve stem height so you are back to the shim adjustment range.

  8. #8
    n00bie On a Mission


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    Quote Originally Posted by Kumansukme View Post
    yep I have had valve seats replaced. They mill out the old one, machine a new seat to fit, then it's back to cutting a new valve seat in the new material. Manuals will tell you the finished valve stem height so you are back to the shim adjustment range.
    Dumb question...?.
    Why would only one valve seat "run out of meat"...
    and not more ? Exhaust or inlet ?
    Can you not just grind the valve stem to give shim variances to play with..???.

    Smart answer required..please.

  9. #9
    n00bie


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    OK I will have a go at the meat issue first. Most likely is the valve clearances have not been checked often enough. For most shim adjusted engines the clearance decreases with use, opposed to rocker and tappet adjusters that usually get larger clearances. When clearances are too small the valve can remain slightly open and exposed to combustion temperatures not just exhaust where most of the energy has already burnt. So both the valve and the seat become super hot and soft, leading to rapidly increasing wear. The valve can get so hot and soft it actually tries to pull itself through the seat. Also the valve would normally shed it's heat through the valve seat, to the ally head and then to the cooling air, the cut in the chain leads to even higher temperatures. It's like a snowball effect and your engine can deteriorate quickly. Hope that explains "run out of meat". It may have been a faulty valve or seat but I think that would show itself early in life, not wait till now.
    Yes you can grind the valve stem to adjust clearances but there is a limit. If you grind off too much the collets can sit proud of the stem and as soon as the cam lobe sweeps around the collets are loosened allowing the valve to drop into the combustion chamber, not a good result.
    Now Glen you have been around for a while so might I suggest not asking for a "smart answer", you are more likely to get a smartarse answer.

  10. #10
    n00bie On a Mission


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    Quote Originally Posted by Kumansukme View Post
    OK I will have a go at the meat issue first. Most likely is the valve clearances have not been checked often enough. For most shim adjusted engines the clearance decreases with use, opposed to rocker and tappet adjusters that usually get larger clearances. When clearances are too small the valve can remain slightly open and exposed to combustion temperatures not just exhaust where most of the energy has already burnt. So both the valve and the seat become super hot and soft, leading to rapidly increasing wear. The valve can get so hot and soft it actually tries to pull itself through the seat. Also the valve would normally shed it's heat through the valve seat, to the ally head and then to the cooling air, the cut in the chain leads to even higher temperatures. It's like a snowball effect and your engine can deteriorate quickly. Hope that explains "run out of meat". It may have been a faulty valve or seat but I think that would show itself early in life, not wait till now.
    Yes you can grind the valve stem to adjust clearances but there is a limit. If you grind off too much the collets can sit proud of the stem and as soon as the cam lobe sweeps around the collets are loosened allowing the valve to drop into the combustion chamber, not a good result.
    Now Glen you have been around for a while so might I suggest not asking for a "smart answer", you are more likely to get a smartarse answer.
    Lol

 

 

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