can i correct a warped brake disc ?

[Anthony]

my right front brake disc is warped :
when measuring with dial clock i found a 0,30 mm warp, mostly on 1/6th of the disc.
most part stays flat, but one half goes down with a peak.
according to the honda service manual the service limit is 0,30mm : replace if higher

the question :
can i 'bend' a disc back into place ?
one of my work buddies claims it can be done, with a big wrench.

i am not feeling very comfortable with messing with my brakes, but i want your opinions before i get a new set of discs

history :
98 standard, 60.000 kms
3 months ago i found out my brake caliper was bent (see here : http://www.valkyrieforum.com/bbs/index.php/topic,27156.0.html ) ,
and i replaced the brackets with 6 piston fixed mounted calipers from Pretech.
i centered the calipers around the disc with the delivered shims, and set off for a 5300 mile trip to European Inzane 5 around Sweden, Norway, Finland, Denmark, Germany,  ...
During he first 2k kms of the trip i felt the new pads were setting in on the original disc (wearing off the outer rim the OEM pads had left on), so i was not worried about a little rattling and shaking when braking hard.

but the rattle did not go away, so finally i took a dial clock on the discs and found that 0,30 mm warp (left disc = 0,04mm).
Come to think of it, even with my OEM calipers, i always heard a minor grind when rotating the front wheel, that i did not suspect much.
Problems is that the Pretechs are mounted fixed, where the OEM Nissins are "floating" around the discs.

the Pretechs bite hard,
in combination with the new stainless brake lines, i have more feel and a very short brake lever movement between no and ALL stop,
but i am not comfortable with the rattle and what it does to the pistons.

can i fix this or should i get new discs without thinking about messing with it ?

TiA,
Anthony

[iliveforcurves]

I would try to straighten it with a hydraulic press rather than using a wrench.  I used to flatten machined rings with a press at my last job.  They had a flatness callout of .001 inch.

[Disco]

I'm sure it can be done.  I've never done it, but if I ever tried, I would use a press and not a wrench.

[The Anvil]

I've seen it done on bicycle discs (with wrenches) but I would not do it with a motorcycle disc. There are so many things that can go wrong...

[TomE]

Well, if the choice is replacement or repair, why not give it a try? The worst that will happen is that you will need to buy new disks, right?  The only thing at risk is your time.

I have never tried this specific repair, but I have shaped metal with a Crescent wrench while building trailers. I am sure that you can bend the things with a wrench and a vice, but I suspect that you will need to be careful that you don't move the outer rim more than the inner rim. 

A hydraulic press, or even a very big vice, might be able to put the pressure just where it is needed to get the disk flat from center to edge as well as along the "length" of the disk.

[Farther]

Get new ones and be done with it. 

[Ricky-D]

Anthony, I bought a rotor from (maybe you) that was screwed up from a disc lock not being removed when starting.

The rotor would be out of alignment because the inner center element was the part that was bent.

So I concentrated on straightening out the center piece and the rotor came back into alignment.

I can't understand how the rotor could be out because it's a pretty hefty piece of steel.

Sure, with the six piston calipers I can see where you will experience greater problems if anything with the rotor is out of whack.

Look to the inner holder for your problem because I don't think it is the rotor itself.

Since a new caliper bracket is available I would suggest going back to the stock set up and forget the bling. The stock Valkyrie front brakes are renowned for their braking ability.

***

[Anthony]

Anthony, I bought a rotor from (maybe you) that was screwed up from a disc lock not being removed when starting.
The rotor would be out of alignment because the inner center element was the part that was bent.
So I concentrated on straightening out the center piece and the rotor came back into alignment.

no , it wasn't me selling you anything, but you are right : i should also check the center piece.
right now i am preparing for a trip to China, but i'll check that when i get back home.
the only thing i have to lose is a bit of time.
At work i have access to enough machinery : presses, turning machines, ... so i will find something that can deliver enough force to bend it if necessary.
and if i overdo it, i still have the same alternative : buying new ones.

i will keep you updated when i'm there,
Thanks,
anthony

[The Anvil]

Well, if the choice is replacement or repair, why not give it a try? The worst that will happen is that you will need to buy new disks, right?  The only thing at risk is your time.

I have never tried this specific repair, but I have shaped metal with a Crescent wrench while building trailers. I am sure that you can bend the things with a wrench and a vice, but I suspect that you will need to be careful that you don't move the outer rim more than the inner rim. 

A hydraulic press, or even a very big vice, might be able to put the pressure just where it is needed to get the disk flat from center to edge as well as along the "length" of the disk.

No there are other risks. Metal can only be cold worked or formed so many times before you get things like microfine cracks that eventually turn into big cracks due to heat cycles. A cracked front rotor can be catastrophic.

[Grandpot]

Buy new!  End of advice.

[TomE]

Well, if the choice is replacement or repair, why not give it a try? The worst that will happen is that you will need to buy new disks, right?  The only thing at risk is your time.

I have never tried this specific repair, but I have shaped metal with a Crescent wrench while building trailers. I am sure that you can bend the things with a wrench and a vice, but I suspect that you will need to be careful that you don't move the outer rim more than the inner rim. 

A hydraulic press, or even a very big vice, might be able to put the pressure just where it is needed to get the disk flat from center to edge as well as along the "length" of the disk.

No there are other risks. Metal can only be cold worked or formed so many times before you get things like microfine cracks that eventually turn into big cracks due to heat cycles. A cracked front rotor can be catastrophic.

Granted, there are other risks. If you bend it enough times, it could crack. And if you don't bend it that much, you might get a good rotor out of the process. But metal can be worked, if a guy wants to do it.

 Again, if a guy wants to give it a try, why not? It's a free country, right?

[The Anvil]

Well, if the choice is replacement or repair, why not give it a try? The worst that will happen is that you will need to buy new disks, right?  The only thing at risk is your time.

I have never tried this specific repair, but I have shaped metal with a Crescent wrench while building trailers. I am sure that you can bend the things with a wrench and a vice, but I suspect that you will need to be careful that you don't move the outer rim more than the inner rim. 

A hydraulic press, or even a very big vice, might be able to put the pressure just where it is needed to get the disk flat from center to edge as well as along the "length" of the disk.

No there are other risks. Metal can only be cold worked or formed so many times before you get things like microfine cracks that eventually turn into big cracks due to heat cycles. A cracked front rotor can be catastrophic.

Granted, there are other risks. If you bend it enough times, it could crack. And if you don't bend it that much, you might get a good rotor out of the process. But metal can be worked, if a guy wants to do it.

 Again, if a guy wants to give it a try, why not? It's a free country, right?

I didn't say he can't but he should be aware of the risks and they're potentially life threatening. A broken brake disc can get you killed lickety-split.

Let's say you do get it worked into a serviceable condition (highly unlikely in the first place but not impossible) but you cause damage not visible to the eye. Let's then say that you get that disc nice and hot and then maybe go through a puddle and give it a good thermal shock (often how they got warped in the first place). The disc could crack, maybe a little, maybe a lot. Sometimes that means a dramatic loss of braking performance and a lot of noise. Sometimes it means a disc in pieces in direct interference with the pad and caliper. Imagine the danger that poses.

[Ricky-D]

Too much scare talk!

He's not going to do that!

***

[R J]

Just dig down in the damn old moldy sock and come up witrh enough  $$$$ to replace them.

I put a set of Honda's front rotors on MGM at about 65K, put the EMC's on it at 120K and still running them at 242K.   Make sure you use EMC pads with them.

[TomE]

Shattered disks? Color me skeptical. I am sure it's possible, but still....

Another option might be to grind the disk flat. The same guys the grind flywheels flat can work on the disks, I am told.  0.030 may be a lot of grinding, but judging from when I looked into this for my GL1000, it's possible. The guys on the Naked Goldwing Board agreed on this solution, and a flywheel guy I talked to in Portland was willing to give it a try. In the end, my GL1000 disks are not warped very bad at all, and I ended up ignoring it, so I have not actually tried it.

[TomE]

So I did a little bit of research on disk brakes, being the curious guy I am, and I find myself much less skeptical about cracked disks now. Take a look at this:

http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

It seems that disks can crack, since they are cast. It also seems that many cases of "warped disks" are not really warps at all, but uneven deposits of pad material on the disk.

That face grinding might be a better choice than bending.

Another option, mentioned in the link, is to change to a good pair of Semi-Metallic pads. They are more abrasive, and may scour the deposits left on the disk by hard use, making it smoother. I think I want to give this one a try myself.

[The Anvil]

Shattered disks? Color me skeptical. I am sure it's possible, but still....

I take it you've never seen a disc broken clean in half?

[Ricky-D]

I take it you've never seen a disc broken clean in half?

I am sure this is referring to automobile rotors which are generally speaking, castings. Castings which are of a minimum quality when considering the whole range of iron castings. Automobile rotors are machined directly from the castings.

Motorcycle rotors are forged after casting, prior to machining, to impart a much more homogenous and concentrated internal matrix structure.

Motorcycle rotors are also investment castings of a much higher quality of materials when compared to cast iron. Such as stainless steel and other alloys of steel.

Some motorcycle rotors are made from ceramic materials. I think these could possibly break.

***

[The Anvil]

I take it you've never seen a disc broken clean in half?

I am sure this is referring to automobile rotors which are generally speaking, castings. Castings which are of a minimum quality when considering the whole range of iron castings. Automobile rotors are machined directly from the castings.

Motorcycle rotors are forged after casting, prior to machining, to impart a much more homogenous and concentrated internal matrix structure.

Motorcycle rotors are also investment castings of a much higher quality of materials when compared to cast iron. Such as stainless steel and other alloys of steel.

Some motorcycle rotors are made from ceramic materials. I think these could possibly break.

***

Nope, motorcycle (GS500) rotor snapped in two pieces.

[Robert]

Why would anyone straighten a disc? That is dangerous and there isn't enough metal on the disc to have any room for mistakes. Besides that the Valk rotors  are floating rotors and misalignment can lead to catastrophic failure. Then there is the issue that you can mar the surface of the disc and there is no machining it because they are already probably worn below specs. If you are one or two thousands out of spec and there is no damage to the mounting or to the rotor itself then it may be possible. But most rotors that pulse may not show the real extent of their warpage until they get heated by the brakes and most rotors are already off by a few thousands and not pulsing anyway. So how are you going to determine how much to bend back and where?  Also there is metal memory so you bend it now weaken the metal and when it heats up it goes back to the prebend position. This is why machining is the only acceptable way to straighten a rotor and the Valk rotors are already to thin after some wear usually to be alble to be machined as they are below spec. Its pretty risky buisness especially if it is the front. If your braking hard and something happens to that rotor its not a position I would ever want to be in. You risk your own life and the life of anyone around you. To me its no different than the guy with a bald tire ridding on the highway it blows out and he lives but kills someone else.