Disc warpage

Greetings all! When I bought my GPz900 it came complete with a set of
prewarped front rotors, which stopped the bike fine, but gave annoying
feedback. I purchased a newsed set off eBay, which were absolutely straight
and well within acceptable limits of wear. I used fresh pads, and my
calipers are in as new condition, both free and smooth.I "broke in" the new
pads and rotors in the same manner I've used on a couple of hundred sets of
pads on my vehicles (messenger, go through a LOT of brakes), progressively
harder stops then let it sit and cool completely. Now, after 5 or 6000
kilometres and a couple of hard stops from triple digit speeds, the newsed
rotors are warped as well. Other than my riding style, (remember I didn't do
the damage to the first set) any suggestions on the cause of this recurring
phenomena?

Also, I read a post somewhere, about "cooking " rotors straight again. Has
anyone ever tried this, and if so what method was used to keep the rotor in
the what position in the oven? On their edge? flat on a piece of steel? On
the grill?

TIA!

Tom B

 

I've seen a write-up about tweaking rotors straight. It involved a dial
gauge and wrenching on the central rotor basket, a bit at a time. Never
tried this myself.

 

Heat, pure and simple. The rotors didn't expand uniformly, and they
warp as a result. The amount of heat generated is tremendous - all
the energy "stored" in 600 pounds of motorcycle and rider going at
warp speed gets converted to heat in just a few seconds.

Cool idea, if it works. You'd have to get 'em pretty hot, and have
'em on a very flat surface I'd suspect. Maybe in an oven during its
cleaning cycle?

Mark Hickey

 

This supposed "rotor warping" was a big deal in the early 1980's and I
had to take my GS-1100 back to the $tealer$hip six times to get them to
replace the front wheel.

The rotors weren't warped at all, the brake mounting surface of the
front wheel was machined slightly off perpendicular to the axle, so
that meant the the disks weren't perpendicular to the axle either.

I pointed out to the owner of the $tealer$hip that Kawasaki's large
diameter brake mounting surface shouldn't be as critical as the small
diameter surface on the Suzuki.

In a few weeks, he was telling that analysis back to me as if he'd
thought of it himself.

It may just be possible that your front wheel bearings are worn enough
on one side to cock the axle a little, or that you installed the front
wheel incorrectly and didn't get it centered between the fork legs.
Maybe the whell moved slightly to one side when you tightened the front
axle.

Honda solved brake rotor warpage problems by "indexing" each rotor to
bring the rotor run out to within specification so they could refuse to
warranty rotors that weren't quite warped enough.

Indexing involves removing all the bolts in each rotor and turning it
one sixth of a turn, reinstalling and retorquing the bolts and doing
the run out check until you get the least amount of runout.

There is the possibility that you may have damaged the thread on one of
the bolt
holes, raising the first thread slightly. This would cause apparent
rotor runout because the rotor mounting flange wouldn't sit squarely on
the wheel.

If you find a raised thread, you can carefully file it down.

 

It might be a good idea to check the rotor mounts for distortion/runout
using a dial gauge

Leon

 

The carrier plate for mine was slightly cocked in
a simmilar manner.

I shimmed it back to true with a couple thicknesses
of aluminum foil between the carrier plate and the
wheel. Got rid of about a .01" wobble and smoothed
out the braking tremendously.

My bet is that this was the result of getting banged
around during a tire changing operation.