Topic: CB550 K1 Brake Disk Thickness

[DiscoEd]

Howdy,
I'm hoping to clean up my front brake disk on my CB550 K1 a bit. I can get setup to turn it in a lathe, but I can't seem to find any specification for the minimum thickness of the disk. (I'm not really looking to take a lot of material off)

I did find a flatness spec in the Clymer manual of 0.3mm.

Does anyone know what the minimum thickness specification for the disk is?

Thank you,
DiscoEd

[csendker]

According to my Shop Manual:

Friction disc thickness:

-Standard value: 3.3 mm (0.13 in)
-Servicable limit: 3.0 mm (0.11 in)

Disc trueness:

-Standard value: N/A
-Servicable limit: 0.3 mm (0.011 in)

(edited the trueness to be correct at 0.3 mm)

[DiscoEd]

Thank you Chris.

That sure is a pretty interesting difference for the flatness spec between what your shop manual says vs. Clymer.

Regards,
DiscoEd

[csendker]

The book is a bit blurry...8?...3?  I should probably check the conversion.....

Ok, just checked.  It should be 0.3mm, which does in fact convert to 0.011 in.  My bad.

[csendker]

The disc thickness numbers check out OK.

[DiscoEd]

Chris,

I never even thought of doing the conversions.

Thank you,
DiscoEd

[DiscoEd]

According to my Shop Manual:

Friction disc thickness:

-Standard value: 3.3 mm (0.13 in)
-Servicable limit: 3.0 mm (0.11 in)

Disc trueness:

-Standard value: N/A
-Servicable limit: 0.3 mm (0.011 in)

(edited the trueness to be correct at 0.3 mm)

Chris,
This morning I threw a set of calipers on the two rotors that I have, one off of a '75 and one off of a '76 CB550. Both of them have a thickness of 0.275" and 0.278" respectively (close to 7mm). This is more than twice the dimensions that you posted. Are the figures you posted actually for the clutch friction discs?

Best Regards,
Ed

[bwaller]

I think there is some confusion with which disc here. The brake disc rotor minimum thickness is 6mm, it is embossed on the back of the disc carrier. I've had this discussion many times with machinists, lathe or rotary table or grinding to remove stainless disc material. The concensus in this forum was to grind. I have seen them vibrate in a lathe when being machined, but this was a rotor off a roadracer that had been heated lots, so that might have been the problem.   

[csendker]

Hmmm, now that you mention it, that would be a mighty thin disc.  The manual doesn't specify anything beyond "Friction Disc Thickness", but I noticed it's not in the brake section, so I suspect it may be for the clutch. 

bwaller has nailed it though.  I looked and sure enough, right on the back of the disc it says "minimum 6mm"; I circled it in the picture.

[DiscoEd]

The brake disc rotor minimum thickness is 6mm, it is embossed on the back of the disc carrier. I've had this discussion many times with machinists, lathe or rotary table or grinding to remove stainless disc material. The concensus in this forum was to grind. I have seen them vibrate in a lathe when being machined, but this was a rotor off a roadracer that had been heated lots, so that might have been the problem.   

I'll have to look mine over in the morning and see if I can find that dimension stamped on the back of the disc carrier. The condidtion of my rotors is pretty good, so very little material will have to come off.

We had this discussion about to lathe or grind. I think we were leaning away from grinding. There was some concern about making the surface so smooth that there wouldn't be enough grip. I'm not sure which path my machinist is going to go down, but this is guy who could turn space shuttle parts on a harbor freight wood lathe with success. So I trust his judgement.

Regards,
DiscoEd

[bwaller]

Let me know which route you take re the machining, I've got a pair to flatten and haven't yet decided the best approach. Sounds like your guy should know.

[DiscoEd]

Let me know which route you take re the machining, I've got a pair to flatten and haven't yet decided the best approach. Sounds like your guy should know.

Will Do! I should have the end result in hand on Monday.

(BTW...yep you were correct the markings are on the back of the disc carrier)

Regards,
DiscoEd