TOPIC:

Just took my rear rotor off while changing tires. Noticed a nice big crack in it. Glad I found it. Cost of finding it? Priceless. Cost of new rotor. $150 bucks. Come on man. WTF? This is getting ridiculous!!!! 

All I can tell you is, rear disk is thicker than front one. So not only the diameter, but you need to pay attention to the thickness of the rear.

My 750 have all three at same diameter, but rear is significantly thicker (i8f I'm not mistaken, rear min. thickness is at 6mm, where front is at 4.5 mm.) so just be careful when you look for the replacement.

Also, parts are too expensive? Try living middle of no where. I can't get this, They won't ship that even when I'm willing to pay for the shipping. On top of that, Amazon is the only supplier willing to do free shipping. I have to pay for parts + shipping, usually 2nd day air price. Why? I have no f**king idea. If you go to UPS or FedEx site, they do offer ground shipping, but when you call the supplier, they all tells me they don't have it!  And for some reason, they won't ship USPS.

Lastly, I'm a fan of 750's. So I could be wrong for the bigger Kawasaki's.

Ojisan rider wrote:

All I can tell you is, rear disk is thicker than front one. So not only the diameter, but you need to pay attention to the thickness of the rear.

My 750 have all three at same diameter, but rear is significantly thicker (i8f I'm not mistaken, rear min. thickness is at 6mm, where front is at 4.5 mm.) so just be careful when you look for the replacement.

Also, parts are too expensive? Try living middle of no where. I can't get this, They won't ship that even when I'm willing to pay for the shipping. On top of that, Amazon is the only supplier willing to do free shipping. I have to pay for parts + shipping, usually 2nd day air price. Why? I have no f**king idea. If you go to UPS or FedEx site, they do offer ground shipping, but when you call the supplier, they all tells me they don't have it!  And for some reason, they won't ship USPS.

Lastly, I'm a fan of 750's. So I could be wrong for the bigger Kawasaki's.

Sounds like a nightmare ! where in the world are you ? I don't think the thickness is absolutely critical as there is enough travel in the piston to compensate. "Min thickness" figures are a "wear limit" as opposed to a specification as such
PS: that's crazy money for a "one piece" rotor 

The minimum disc thickness is specified in the manual.  Any replacement should be thicker than that number.

hardrockminer wrote:

The minimum disc thickness is specified in the manual.  Any replacement should be thicker than that number.

HRM appreciate what you are saying but I'm going to disagree (happy to be challenged on this) the minimum thickness in the manual is a "wear limit" based on the starting thickness of the "OE" rotor - if you where running oversized pistons would you still use the "wear limit" specification stated in the manual for cylinder bore diameter?
Any replacement rotor should be marked with a "wear limit" minimum thickness figure relevant to that specific part (if it's not marked up then it's probably garbage) 

PS: To be fair any replacement part of even moderate quality should be close enough to OE specs that it a bit of a "mute point" 

Wookie58 wrote:

hardrockminer wrote:

The minimum disc thickness is specified in the manual.  Any replacement should be thicker than that number.

HRM appreciate what you are saying but I'm going to disagree (happy to be challenged on this) the minimum thickness in the manual is a "wear limit" based on the starting thickness of the "OE" rotor - if you where running oversized pistons would you still use the "wear limit" specification stated in the manual for cylinder bore diameter?
Any replacement rotor should be marked with a "wear limit" minimum thickness figure relevant to that specific part (if it's not marked up then it's probably garbage) 

PS: To be fair any replacement part of even moderate quality should be close enough to OE specs that it a bit of a "mute point" 

What you are saying Wookie is that it's OK to ignore factory wear limits. 

The wear limit is based on more than just the starting thickness.  It's there for reasons an engineer considered in the brake design and you and I don't know what they were, but I can imagine they considered heat dissipation along with stress on the system, among other things.  As an engineer I learned long ago to give the best advice I can give, and that doesn't include ignoring factory wear limits.  I know this is an internet forum and people can accept or reject what advice they are given, but I believe I have an obligation to think about what it will mean in the longer run.  Anything less is just unprofessional in my opinion.

To answer your question...I would not be running oversize pistons, but if I did I would be talking to a brake specialist or two about the design change and it's implications.  Brakes are a critical system on a motorcycle and should be the best quality they can be.  

I can appreciate the discussion about this. Wear limit wasnt my issue. It was cracked. And also found 2 more cracks upon closer inspection. I hope EBC brand lasts for a while. 

Beaner242 wrote:

I can appreciate the discussion about this. Wear limit wasnt my issue. It was cracked. And also found 2 more cracks upon closer inspection. I hope EBC brand lasts for a while. 

EBC are normally perfectly OK

PS: ref the wear limit discussion, apologies this sometimes happens where threads open a new debate 

Wookie58 wrote:

Beaner242 wrote:

I can appreciate the discussion about this. Wear limit wasnt my issue. It was cracked. And also found 2 more cracks upon closer inspection. I hope EBC brand lasts for a while. 

EBC are normally perfectly OK

PS: ref the wear limit discussion, apologies this sometimes happens where threads open a new debate 

oh I know. I wasn’t complaining 
 

hardrockminer wrote:

Wookie58 wrote:

hardrockminer wrote:

The minimum disc thickness is specified in the manual.  Any replacement should be thicker than that number.

HRM appreciate what you are saying but I'm going to disagree (happy to be challenged on this) the minimum thickness in the manual is a "wear limit" based on the starting thickness of the "OE" rotor - if you where running oversized pistons would you still use the "wear limit" specification stated in the manual for cylinder bore diameter?
Any replacement rotor should be marked with a "wear limit" minimum thickness figure relevant to that specific part (if it's not marked up then it's probably garbage) 

PS: To be fair any replacement part of even moderate quality should be close enough to OE specs that it a bit of a "mute point" 

What you are saying Wookie is that it's OK to ignore factory wear limits. 

The wear limit is based on more than just the starting thickness.  It's there for reasons an engineer considered in the brake design and you and I don't know what they were, but I can imagine they considered heat dissipation along with stress on the system, among other things.  As an engineer I learned long ago to give the best advice I can give, and that doesn't include ignoring factory wear limits.  I know this is an internet forum and people can accept or reject what advice they are given, but I believe I have an obligation to think about what it will mean in the longer run.  Anything less is just unprofessional in my opinion.

To answer your question...I would not be running oversize pistons, but if I did I would be talking to a brake specialist or two about the design change and it's implications.  Brakes are a critical system on a motorcycle and should be the best quality they can be.  

HRM I think we are going to need to "agree" to "disagree" on this one. I never said "ignore factory wear limits" but rather said if using a non OEM component then refer to the component manufacturers specification (which is what the factory do in the first instance within their FSM's) the reference to pistons related to the engine, I would also not attempt to oversize a brake cylinder (this was simply an example that you can't always go by the factory data)
Based on your rational I am "taking my life in my hands" with my current build ref brake rotor thickness 
Stock 1982 KZ1000K front discs New 4.8mm - 5.1mm - wear limit 4.5mm
ZX9R (marginally lighter but significantly faster) components being used front discs new 3.8mm - 4.2mm - wear limit 3.5mm 
Strangely enough both have a wear limit approx 0.5mm (in large handfuls) below their starting thickness at manufacture !!!!

I basically had to use a breaker bar to get the corroded bolts out of rotor. Do I guys use anti seize on your bolts? Or lock tight?

Personally I would favour new bolts and blue loctite (only my opinion)