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cb750 racing frame

This is a discussion on cb750 racing frame within the Project Builds forums, part of the Caferacer.net Forums category; finally getting around to starting the frame for my cb750, "sketched" it out in 1/4 rod, any thoughts? the top tubes are going to be ...

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Thread: cb750 racing frame

  1. #1
    Senior Member roccitycafe's Avatar
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    cb750 racing frame

    finally getting around to starting the frame for my cb750, "sketched" it out in 1/4 rod, any thoughts? the top tubes are going to be 1-1/4" along with the two tubes going down to the front engine mounts, the rest will be 1", the black foam is where mounts will be welded to the valve cover. the subframe will either be aluminum tube or possibly carbon fiber, in which case the whole seat/tail section would be one piece of carbon. the swingarm will possibly be connected to the shock through a linkage where the shock is mounted to the underside engine mounts

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  2. #2
    Banned Witworth's Avatar
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    Forget using the valve cover as engine mounts. It's dumb and unnecessary on so many levels. The old heavy cases should be plenty strong enough to use as a stressed member.

    Draw the bike up in real scale on a wall in chalk. Plenty of famous frame builders did it that way back in the day. Base your geometry on a fast stable bike like a GSXR1100K. Stable for the road, motoGP flickable is for the race track.

    You might not have the ground clearance to use a Buell type shock using a 4 : 1 pipe. Do something different, twin shocks like a TT rotary Norton maybe?

    Check out Google pictures on how Egli uses big alloy frame plates at the rear of the motor. It's strong and pretty easy to fabricate. It's also far easier to change the frames design if you have F*&^ed up totally at first.

    Make the seat subframe in mild steel tube to begin with, and make it so you can easily bolt alternative ones on later. Bear in mind all the café fashion seat subframes are only poor copies of motoGP ones, and they are nowhere near strong enough and safe enough for road use for fat old Gino from Jersey to ride. Triangulate or die.

    Danger, is my business."

  3. #3
    Senior Member roccitycafe's Avatar
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    how is it dumb and unnecessary??? I can't believe I'm talking to a bot.

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  5. #4
    Senior Member monkey's Avatar
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    The carbon subframe thing works out great.... too bad CB750's are such heavy lumps of crap.
    I have no love for inline 4 cylinder motorcycles.... they sound like sewing machines.
    latered

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    Senior Member CAPTAIN AWESOME's Avatar
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    Looks like the top rails may need some more bracing where they bend towards the neck?

    What thickness tubing?

  7. #6
    Senior Member roccitycafe's Avatar
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    either .08 or .06 on the 1.25, and .06 on the 1"

    I'll box in the neck area with sheet gussets

  8. #7
    Senior Member roccitycafe's Avatar
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    Quote Originally Posted by monkey View Post
    The carbon subframe thing works out great.... too bad CB750's are such heavy lumps of crap.
    I have no love for inline 4 cylinder motorcycles.... they sound like sewing machines.
    yeah, I would love a better engine, but it's what I've got at the moment, and it's already built to 900 so I'll keep improving the handling and shedding weight. you think the carbon subframe idea isn't crazy?

  9. #8
    Banned Witworth's Avatar
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    Quote Originally Posted by roccitycafe View Post
    how is it dumb and unnecessary??? I can't believe I'm talking to a bot.
    Well if Egli, Seeley, Rickman, Bimota and Moto Martin didn't think a head steady was necessary on a sohc custom sports frame, I believe them.

    There are plenty of reasons why your idea of using the valve cover as a mount is daft. I'll tell you if you want.

    You need to study Moto Martin frames design.

    Danger, is my business."

  10. #9
    Senior Member monkey's Avatar
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    The carbon subframe idea works. I did this on one of my race bikes back in 2004.
    It was super light and strong... I would visit this again.... however I am working on other things right now
    latered

  11. #10
    Senior Member roccitycafe's Avatar
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    I would imagine they didn't spec one because they used off the shelf engines and the frames were designed around that fact, using the head to help triangulate the neck is used quite a bit, but if you've got a ton of reasons I shouldn't, then go for it

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