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  1. #1
    CB750 Enthusiast KIRBY's Avatar
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    Replace Vulnerable Primary Chains With Gears?

    I've been told that the most vulnerable part of a CB 750, when increasing power, are the primary chains. Has anyone considered replacing the primary chain sprockets with gears for higher power handling?

  2. #2
    CB750 Guru amc49's Avatar
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    There is a New Zealand roadracer that does it on the DOHC, but the conversion is super megabucks............

  3. #3
    CB750 Enthusiast KIRBY's Avatar
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    So.....All my ideas are expensive.

  4. #4
    Moderator dirtdigger's Avatar
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    It has been done on the sohc but again, gears are super expensive to have designed and built. On top of that you have to do something with the crank as it has sprocket not a gear.

  5. #5
    CB750 Guru amc49's Avatar
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    The DOHC technically uses a sprocket too, but it is one for Morse Hy-Vo type timing chain. That type of sprocket can be made as a gear-to-gear connection one and what he did there, the gear would have slightly odd shaped teeth but works as a gear anyway.

    And yes, to answer a previous statement, one of the greatest problems with your ideas is that they all will be as expensive to make as a jet fighter. The ideas CAN be done in physicality, but it takes a corporation to be able to amortize the ideas enough to be worth it.

  6. #6
    CB750 Addict Medyo Bastos's Avatar
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    Mirko is working on it here ~> https://r.tapatalk.com/shareLink?sha...0&share_type=t Geared Primary Drive



    Sent from my iPhone using Tapatalk

  7. #7
    CB750 Enthusiast KIRBY's Avatar
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    With only 2 gears, doesn't he spin the gearbox backwards?

  8. #8
    CB750 Enthusiast leo750k's Avatar
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    my mother always used to say to me "Ya you have Champagne taste, on a beer pocket book"

  9. #9
    CB750 Guru amc49's Avatar
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    You put an idler in the middle for a 3 gear train, that keeps the proper spinning direction in place.

    I envision problems with that SOHC design, the sprung hub is going to be an issue. The DOHC one survives by using much smaller damping mechanism there, and even that may be gone now to use just the clutch basket as the damper there. Can't say. The first one used the OEM shell and the outer disintegrated under hard power, the inside damper blades that were separated by the damper rubbers moved under big power to crack the whole thing up.

    You want a crank damper to absorb vibration, it stops crankshaft breakage, but you also want solid gears there to carry bigger power. The SOHC gear shown in the link is likely to break up under power, the spring damper renders it too weak.

  10. #10
    CB750 Enthusiast KIRBY's Avatar
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    Quote Originally Posted by amc49 View Post
    You put an idler in the middle for a 3 gear train, that keeps the proper spinning direction in place.
    Yes, but I don't see one in his design.

  11. #11
    CB750 Enthusiast KIRBY's Avatar
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    Here's an idea. Remove the chain. Put a speciallyClick image for larger version. 

Name:	Sprocket to Sprocket Idler.JPG 
Views:	9 
Size:	29.8 KB 
ID:	9177 engineered idler between the two primary sprockets. I know the relative sizes of the sprockets is wrong, but this is just to demonstrate the idler with teeth that fit the chain runs. If the chain teeth need reinforcing, the space between the two runs can be filled in by a split piece machined to match the sprocket teeth.
    Last edited by KIRBY; 10-20-2019 at 03:52 PM.

  12. #12
    CB750 Guru amc49's Avatar
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    I do not grasp that last sentence at all.

    The pic there is how the DOHC does gear drive.

    In the link he mentions 'idler carrier' and how he is going to mount it more than once in the post, you have to understand that means a third gear, the other two need no carrier as they are part of either driver shaft or driven shaft.

    I was likely incorrect on the post 9, that gear shown with the springs is the clutch one thinking, you need some sort of shock absorption there. I'm not big though on how weak the hub there is, it should break pretty quick, there is not nearly enough metal support there.
    Last edited by amc49; 10-21-2019 at 05:35 PM.

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