Brake rotor machining?

[breakaway]

Hello,

I've bought a '89 CBR400RR, and one (or both) of the front rotors are warped, causing pulsation. Warped disc. I think its only one, but not sure.

I've heard that it's possible to 'machine' these discs. I'm considering this, as the alternative the shop presented was to buy new discs at $380 each.

Firstly, where in Auckland can I get these disc(s) machined?

Secondly, is there a safety issue with machining as long as there is no pulsing?

Thanks

[klyong82]

If the rotors are warped from heat than straightening will not be the best solution as they can bend easily again, best to buy another set. But if your disc are not straight from an impact then it can be straigtened. The pulsing could also cause you to fail your wof if the inspector deemed it to be unsafe - so get this sorted asap.

Have you tried bucket n bits? they might have some second hands for sale http://www.bucketsnbits.co.nz/

Not sure where in Auckland bike disc machining can be done but I am interested to know also.

[Kwaka14]

Check and see how much the run out is first, that will tell you how thin they're going to get when they are skimmed (if that's what you're talking about) and that will have an impact on the warrantable condition of them afterwards.

[maneac]

ive been looking 4 some 1 2 skim my front 1s but no 1 can cause they r 2 thin 2 fit on the machine new 1s about 800 4 my bike

[Kwaka14]

There's a crowd in Hamilton (sorry forgotten the name) who will make up Rotors and fit them to the existing cage and they're pretty reasonably priced (around 600ish a pair from memory)....

[Grub]

Apparently, the proper way to machine discs is to grind them. They can't be properly done in a lathe. Klyong's post about heat-warped ones sounds pretty sensible so i don't know what you can do really

[breakaway]

Have you tried bucket n bits? they might have some second hands for sale http://www.bucketsnbits.co.nz/

Thanks for that Klyong. I've fired off an email to Buckets N Bits, and hoping they will have something. If not, Spending $380 per disc appears to be my only option.

It COULD be by impact damage, but judging from the condition the rest of the bike is in, it looks as if it's sustained a few falls, but there are no obvious signs of impact damage.

I guess there is no way to be absolutely sure.

Also: Does anyone know of any other wreckers that I could check out?

Edit: I have just spoken to the previous owners, and they just brought something to my attention. One of the shocks (USDs) was set a little higher (a few mm) than the other. Why? I don't know. Perhaps this is what is causing the disc to pulsate? Or perhaps this is what has made it wear out in the first place

[Squiggles]

interesting, but would it have any effect? maybe on the handling id say, as the other shock would just compress more and the axel stay parallel to the ground when the you put weight on it... unless im completely misguided thats what would happen

[breakaway]

I'm not sure, as I know little about suspensions. However, according to the previous owner, this would make the front axle "tilt" a little.

[Max Preload]

Yes. The axle would effectively tilt, but the discs would still run true with the axle centreline. If they're floating discs, they could potentially be moving a little unevenly on the slides, binding and causing vibration on braking, but I doubt it - a warped rotor is the likely culprit.

Before just replacing the discs, remove them and check the hub runout first (if non-floating discs), otherwise check the rotor runout using a DTI.