Brake Rotor Compatibility

[crazyramen]

Anyone have any info on rotor fitment? I have a '79 GS750 that needs a new rear rotor. The few from early 750s on eBay I've found have been very close to the spec limit - I'm wondering if I can widen my search to later years/different models.

Or could I drill out the rivets and get a new disk to attach to it? Any direction on finding resources would be great.

Edit: looks like early 550s have the same P/N

[crazyramen]

Upon doing some more research it seems like I might be able to use this one I've ordered. It's sitting at .247" (with the 6mm minimum being .236"). I'm used to car rotors where you gotta get them turned when you replace brake pads, so I thought .011" wasn't gonna be enough for that, but some posts here say that's not needed for these bikes? Do these look like they can be used with just a quick scotchbrite glaze break? I can catch a nail in the grooves, but none of them seems all that deep.

[Rijko]

does not look too bad to me... will be a bit harder on the pads but nothing major.
I like them turned smooth but tbh i'd say you're good as is.

[Big Block]

I'd run it too. This stuff is getting hard to find these days and it will last a while.

[crazyramen]

Thanks for the feedback y'all I'll scuff it up and run it.

[salty_monk]

Yeah, I'd run it. You can't turn these rotors anyway, you have to find someone to set them up & grind them flat... Not easy!

[crazyramen]

Yeah, I'd run it. You can't turn these rotors anyway, you have to find someone to set them up & grind them flat... Not easy!

Yeah I read some posts here about that and watched some YouTube videos. Looks like it'd take some pretty specialized equipment to do this one right and you'd have to punch the rivets and redo them.

I did see a guy who had a radial table set up on a mill with a sanding pad attached that seemed to work pretty well for this real light finishing work. He was taking <.0005" per pass so he wasn't getting worried about warping it. I'd give it a go if I had a radial table on my mill - seems pretty easy and low risk. His jig is fairly simple too

Found the link if anyone's interested

[Chuck78]

Yeah I read some posts here about that and watched some YouTube videos. Looks like it'd take some pretty specialized equipment to do this one right and you'd have to punch the rivets and redo them.

I did see a guy who had a radial table set up on a mill with a sanding pad attached that seemed to work pretty well for this real light finishing work. He was taking <.0005" per pass so he wasn't getting worried about warping it. I'd give it a go if I had a radial table on my mill - seems pretty easy and low risk. His jig is fairly simple too

Found the link if anyone's interested

Thanks for posting that! I'd long been wondering how I could possibly resurface rotors myself, as cutting with a tool steel bit in the lathe would not leave a consistent finish across the outer to inner diameter due to the varying surface speeds based on the diameter changing, a surface grinder type operation would be necessary... a 3M Roloc sanding disc pad was not something I'd considered! I have a rotary table aka turntable "radial table" as you call it, and an old Enco RF30 round column vertical mill, I'll definitely make use of this technique here.
I'd already heavily considered the modern floating rotors presenting more issue with refinishing them evenly, as they are designed to float in and out on those outer rivets, so I definitely would be making some more complex fixturing with adjustable supports to brace the outer rotor ring up from the inner areas directly adjacent to the floating rivets just inside of the pad friction surface on an un-worn factory finished area.
Storm 64 actually came out to advise me on my purchase of the 2 mills and the old South Bend lathe which I bought up in his part of Ohio many years back, thanks again, Norm!

[crazyramen]

Thanks for posting that! I'd long been wondering how I could possibly resurface rotors myself, as cutting with a tool steel bit in the lathe would not leave a consistent finish across the outer to inner diameter due to the varying surface speeds based on the diameter changing, a surface grinder type operation would be necessary... a 3M Roloc sanding disc pad was not something I'd considered! I have a rotary table aka turntable "radial table" as you call it, and an old Enco RF30 round column vertical mill, I'll definitely make use of this technique here.
I'd already heavily considered the modern floating rotors presenting more issue with refinishing them evenly, as they are designed to float in and out on those outer rivets, so I definitely would be making some more complex fixturing with adjustable supports to brace the outer rotor ring up from the inner areas directly adjacent to the floating rivets just inside of the pad friction surface on an un-worn factory finished area.
Storm 64 actually came out to advise me on my purchase of the 2 mills and the old South Bend lathe which I bought up in his part of Ohio many years back, thanks again, Norm!

i hadn't thought of surface finish changing with diameter! That makes a lot of sense. I guess cast iron is easy enough to machine that it doesn't make a huge difference with

That video makes it sound like there's not much downward pressure at all so maybe you could get away with some scrap under the rotors on the unworn area to take out the slack?

I got a mill with a vertical head on a bench top horizontal base so I've got about 4 inches of z height BEFORE the vice. A rotary table would be so useful but I think it'd take too much doing to modify one to fit the dovetail that the xy table rides on.