Scored some old school Performance Machine discs for CB750
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Scored some old school Performance Machine discs for CB750

This is a discussion on Scored some old school Performance Machine discs for CB750 within the Technical forums, part of the Caferacer.net Forums category; At least that is what we think they are. I haven't found a name on them yet. Got 2 front discs and a rear on ...

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  1. #1
    Senior Member parkwood60's Avatar
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    Scored some old school Performance Machine discs for CB750

    At least that is what we think they are. I haven't found a name on them yet. Got 2 front discs and a rear on a set of Comstar wheels. Obviously they are not made of stainless

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    Whitworth - The whole Western World economy runs on total lies and BS: I'm a part of the action.

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    Senior Member jaguar's Avatar
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    Very cool!
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    Senior Member CaTacL1sm's Avatar
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    whats going on with the holes on the disc on the bottom? it looks like they were drilled partially over the edge of the disc or that the disc was worn down on the outside to expose the holes... is there a reason behind this?
    Quote Originally Posted by alwhite00 View Post
    Fuck all of you guys. Get into your little circle jerk and have fun. Thought this may be a pretty cool message board but damn, you guys are assholes.

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    Senior Member hillsy's Avatar
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    Quote Originally Posted by CaTacL1sm View Post
    whats going on with the holes on the disc on the bottom? it looks like they were drilled partially over the edge of the disc or that the disc was worn down on the outside to expose the holes... is there a reason behind this?
    At a guess I would say someone has machined down the outside of the disc after it was drilled to suit whatever fork / caliper combo.

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    Banned Witworth's Avatar
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    Quote Originally Posted by CaTacL1sm View Post
    whats going on with the holes on the disc on the bottom? it looks like they were drilled partially over the edge of the disc or that the disc was worn down on the outside to expose the holes... is there a reason behind this?
    They often do it to reduce weight or maybe even to increase the surface area for air cooling. It even might assist dirt being flung off on dirt bike discs. Some brands of current aftermarket discs are like that. The pads don't run right out there, so it's not a braking function concern.

    Danger, is my business."

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    Senior Member CaTacL1sm's Avatar
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    Quote Originally Posted by hillsy View Post
    At a guess I would say someone has machined down the outside of the disc after it was drilled to suit whatever fork / caliper combo.
    that makes sense... however what impact, in conjunction with the drilled holes, would this have on the structural stability of the disc? it seems you're greatly multiplying the chances for cracks and fractures to occur.
    Quote Originally Posted by alwhite00 View Post
    Fuck all of you guys. Get into your little circle jerk and have fun. Thought this may be a pretty cool message board but damn, you guys are assholes.

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    Banned Witworth's Avatar
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    Quote Originally Posted by CaTacL1sm View Post
    that makes sense... however what impact, in conjunction with the drilled holes, would this have on the structural stability of the disc? it seems you're greatly multiplying the chances for cracks and fractures to occur.
    If slots and holes were a serious stress riser in discs, the factories wouldn't do it. They are not an issue.

    Danger, is my business."

  9. #8
    Senior Member parkwood60's Avatar
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    These may even have have the hole cast in, like real race cars. I haven't done much research on them yet. A friend had a similar set market PM
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    Senior Member hillsy's Avatar
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    Quote Originally Posted by CaTacL1sm View Post
    that makes sense... however what impact, in conjunction with the drilled holes, would this have on the structural stability of the disc? it seems you're greatly multiplying the chances for cracks and fractures to occur.
    If you're talking about the outer semi-circled "holes" which are there as a result of the disc being machined down, then they shouldn't pose a risk of cracking the disc.

    In fact, you can pretty much cut any shape hole into a disc as long as the corners are radius-ed (IE: no sharp corners / edges).


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    Senior Member kenessex's Avatar
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    Quote Originally Posted by Witworth View Post
    If slots and holes were a serious stress riser in discs, the factories wouldn't do it. They are not an issue.

    Danger, is my business."
    I have seen failures on racebikes with home drilled discs, but then again I have actually built and maintained and raced race bikes.
    Here is what 15 seconds on the Google showed:





    Looks like the holes might be stress risers after all.
    I also know why brake discs are drilled, not just some speculation on the possible reasons.

    Ken
    Last edited by kenessex; 07-20-2015 at 01:09 AM.
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