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Turning Brake Rotors?

  • Thread starter Thread starter mark m
  • Start date Start date
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mark m

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Where would be a good place to look for someone to turn a set of rotors? I installed a new set of pads this year and the pulsing has never quite gone away...


Mark
 
Most anyone who tries to turn a motorcycle rotor usually ends up trashing it. Motorcycle rotors are much thinner than a car, that along with them sometimes have holes or slots adds up to lots of chatter and big problems. You need to find someone who can grind the rotor instead of turn it. It makes a much nicer job. Mike J
 
Re: Turning Brake Rotors?

mark m said:
Where would be a good place to look for someone to turn a set of rotors? I installed a new set of pads this year and the pulsing has never quite gone away...

Mark
Click to expand...
I don't recommend turning the rotors. Read a factory manual for your model. Compare new rotor spec with the service limit spec.
On my '79 1000E, (front rotors) the difference from new (.21) to service limit (.19) is only .02"
Removing an amount necessary to make them flat again will surely make them thinner than the service limit. Then they'll really warp with any use.
 
On my '79 1000E, (front rotors) the difference from new (.21) to service limit (.19) is only .02"
Removing an amount necessary to make them flat again will surely make them thinner than the service limit. Then they'll really warp with any use.
Click to expand...
On my 82 the service limit is 6mm (0.24"). I will have to check them and see where they are against that. I have to disagree about taking more than 0.020" off. It should only take a very light cut to clean them up or they would be horrible to use. Mine are not that bad at all, just a bit of a nuisance.

If they are knackered, then where do I look for replacements? E-bay? Or elsewhere? I expect new replacements are fantastically pricey and buying used brake components doesn't seem like a great plan to me. They may have the same issues I am dealing with now.

I do have a buddy who is a home machinist, maybe now is the time for a custom set of cast iron rotors... :)


Mark
 
Mark,

My '83 GS1100E had a pulsing lever years ago when it had a relatively low mileage (I don't remember the exact mileage but I think it was under 10,000). The local shop told me this was common with these bikes and that once they were turned they usually didn't warp again. They turned my rotors and I haven't had any problems since. I now have 34,000 miles on it. I'd recommend finding a good local bike shop to do the job.

Joe
 
Mark, I was just trying to point out you don't want to remove too much.
In my case, I would only have .02 if they were NEW. Mine measure at .20 after all these years. So if I had your problem, according to Suzuki, I could only remove .01 and I'd be at the limit already with no material left for future wear. If yours aren't pulsing that bad, you're OK to remove some I guess, especially after what Joe said. I have to wonder why he says (he was told) they won't warp again. I'm not saying they would, but if they're cut thinner than they are now, why couldn't they?
I believe EBC makes rotors for your model. Probably others too.
 
I was told by a dealer that turning rotors was a bad idea. I would look for a replacement set on ebay or check out Dennis Kirk. However new rotors are pretty expensive.
 
Mark, I was just trying to point out you don't want to remove too much.
In my case, I would only have .02 if they were NEW. Mine measure at .20 after all these years. So if I had your problem, according to Suzuki, I could only remove .01 and I'd be at the limit already with no material left for future wear. If yours aren't pulsing that bad, you're OK to remove some I guess, especially after what Joe said. I have to wonder why he says (he was told) they won't warp again. I'm not saying they would, but if they're cut thinner than they are now, why couldn't they?
Click to expand...

No problem, Keith. I understand your concern perfectly, to many people 0.020" is a small amount of material. But I deal with machined items everyday at work and 0.020" is actually a significant cut on many things. If the rotors are too worn, then that option is out.

And it turns out they are... :? I took a quick measurement last night and they are already a touch under the service limit, so they will be going in the scrap pile instead of being reworked.

As for warping again, I think the recut ones should be just as likely to warp as before. The only thing that will change is that the new rotors may have residual stresses in them from manufacture that will warp the rotor when it gets its first few heat cycles. After that, they should be stable.

The pulsing is not that bad at all. At speed it is not noticeable with a solid pull on the lever. The only nuisance is that I get a slip-grip-slip effect when rolling to an easy stop that makes the front pogo a bit and makes it hard to stop smoothly (don't want the cagers to think I'm a newbie with all that wobbling around... :) ).

I am going to look at getting my buddy to work up a set of cast iron rotors with aluminum carriers this winter and I will install them for next season. I will just live with it for the rest of this season.

Mark
 
All this talk about about minimum service limits makes me wonder, what happens if the rotor IS past it's service limit? I'm not sure, doesn't the piston just go in a bit more and make up for it?
Are all the parts in a typical brake system only allowed to travel a certain amount? I know this is a safety issue.
Don't get me wrong, I wouldn't ride on less than service limit rotors, nor suggest someone else do, that's not what I'm saying. I'm saying what happens if you do, because I bet a lot of riders do and don't know it?
 
Riding below a service limit means the rotor will heat up excessively. The engineers designed the rotor to handle a certain amount of heat, the thickness of the rotor plays a big part in that. Hot rotors warp easier, although the cooling holes relieve stress and allow them to cool. changing to different calipers, a popular modification, may cause problems if larger pads are used since a larger pad will change the balance between cooling and heating of the rotor. It's probably best to leave things stock and not try to reengineer brakes too much.

If a groove is cut into the rotor it could fail and the result would be catastrophic to say the least.

Rotors are available used, around 15.00 a piece seems to be the going rate, and that is a better deal than turning them.
 
I think that having the rotors turned too much would bring them below the mass deemed necessary to soak up the heat generated by a vigorous stop. I have never heard of rotors being ground but I like it. Flywheels in dry clutches are ground so that the clutch will have a perfect face to operate on so why not rotors. It could be a more sutle method.
 
3phase said:
I think that having the rotors turned too much would bring them below the mass deemed necessary to soak up the heat generated by a vigorous stop. I have never heard of rotors being ground but I like it. Flywheels in dry clutches are ground so that the clutch will have a perfect face to operate on so why not rotors. It could be a more sutle method.
Click to expand...
Flywheels are far thicker than rotors and don't deal with the friction a rotor does. They operate exactly the opposite from flywheels in that they do their job sliding and flywheels work when they connect.

If a flywheel breaks from being to thin you call a towtruck, if a rotor breaks you get to talk to St. Peter.
 
Yeah, heat dissipation is one of the thoughts I had too.
I never thought about the possible problem of over-heating the rotor because a more modern/multi-piston caliper was used with an older stock rotor. I bet many here have done that, but maybe they don't push their brake set up too far.
I kept mine stock, except for the SS lines and drilling the rotors out. Stock '79 was a solid rotor. I do recommend the drilling though. They run cooler and don't gall like they used to. They don't sqeal like they used to either.
 
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