Warped brake disc

 Ok I know it isn't the most exciting subject in the world, but while the bike was on the center stand  (to fit a new tyre) I could feel the brake disc was probably warped as I tried to spin the back wheel. It was binding in areas and free spinning in others. It has been like that since I've had the bike but it felt a bit worse than before.

I put my DTI on the disc and it confirmed it wasn't true. Well it was true that the disc was not running true...If you see what I mean.

I had painted the wheel while it was off, but the disc felt warped before. Should I remove all the paint from the disc mounting areas anyway? Could that effect the run out?

I couldn't find in the manual what the rear brake disc run out tolerance was, but I guess that it becoming very hard to rotate the wheel in a certain area was not good.

I bought a new EBC brake disc and fitted it to the wheel/bike. I thought I'd check to see what the DTI says and it was worse than my old disc! 

My DTI is imperial and I'm more used to the metric system anyway. But I was getting 1.6 revolutions on the DTI  for the old disc and 2.2 on the new one.

Any ideas ? At least from someone who can read a DTI  Thanks.


 

Hi from memory i think one full revolution is 1mm but don't hold me to that
In the past have put the disc on a thick piece of glass and then checked with a feeler gauge to see what i can get under

First, get all the paint off of the mating surfaces between the wheel hub and the brake disc. .002"- .003" difference in paint thickness at the disc mounting area will translate to .010" at the perimeter of the disc. A disc that's warped more than .010" or mounted incorrectly will be felt in the brake petal or hand lever depending on front or rear. Same thing for variances in disc thickness of more than .005" will feel like pulsing .

What Kawboy said.  Years ago I purchased a near-new bike that had significant pulsing of the front brakes.  I assumed it was a warped rotor but the bike only had a few hundred KM's on it - but the rotor was definitely 'out of true'.  When I took the rotors off to be 'trued' I discovered there was a thin gasket - referred to as a 'damper' that was torn and missing pieces in several places which caused the rotor to be bolted to the wheel unevenly.  Once I installed new gaskets and reinstalled the rotors - no more pulsing.  Bit of a head scratcher - the torn damper must have been installed that way at the factory as the rotors had never been off before.

 

Thanks for the replies. Sorry I was away for a week and didn't look at a screen once. .

I removed the paint from the mounting surfaces which improved it a lot but it was still out more than I was happy with, for a new disc.
So with no chance of mounting the wheel on a lathe, I took the nuclear option and marked the high and low areas with a marker and gently filed each corresponding mounting surface. I must have mounted that disc and wheel on the bike 20 times. until I got a reading of trueness (if that's a word) that was well within tolerance and I felt I couldn't improve upon. I wouldn't recommend anyone taking this route. It's a bodge at best.

I had to wait a couple of weeks for my new brake pads to arrive (well I'm in France) before I tested it.Unfortunately the disc got hot and started to seize again. A rebuild of the master cylinder again I think.

Also it's not firing on the number 6 cylinder again on idle.    Maybe this ethanol riddled, excuse for a fuel they sell, goes off in litterally weeks? I guess I may have to use fuel stabilizer on every fill up...

No "Screens" for week!   That's discipline!  Or maybe just a real need to disconnect for a while and reset from all the insanity in the world. 

I'm no expert on brakes but could this issue be related to a blocked port in the master cyl?

As far as your #6 not firing:  Ethanol related?  From my experience:  I've been filling with "Regular" at the local ESSO for 16 years and it has Ethanol.   I've had no Ethanol related problems.  Bowls are clean, Brass has the typical patina, no build up of crud, no erosion or degradation of parts and good spray patterns,  There's always a yellowish staining in the venturi, down-stream of the jets. Not necessarily a bad thing as it clearly shows the fuel spray/distribution and this staining is easily removed with lacquer thinner. 
If #6 is not firing at all then it's likely Ignition related, specific to that Cyl. =  A bad spark-plug wire, terminal-end.  It would be a serious blockage in the idle circuit to create a No-Fire situation. 

For what it's worth.