Zimmerman Z-Coat Rotor Damage? Follow up Question

[JRSIII]

I recently posted a thread showing some scuff marks on my newly received Zimmerman Z-Coat rotors. I was quickly informed by the members that this was normal and I was worrying about nothing. However, I noticed something last night that I hadn't when I originally posted. Of the two rotors, one has a notch or cutout on the edge. See attached photo. Is this damaged or is this done on purpose? I can't imagine this could be good for balance, unless it is actually done to correct a balance issue due to casting imperfections. In any case, it strikes me as odd that only one of two has this notch. Thanks in advance.

[impactbumper]

nothing to worry in that picture

[KTL]

Yes that is completely normal. It's a machining mark/relief to balance the rotor.

[SweetWaterSurprise]

Agree with what's been posted. Seen it before, nothing to worry about.

[JRSIII]

OK thanks all. I guess the reason that the other one didn't have this was that it was cast perfectly and didn't require balancing?

[seafood10]

Originally Posted by JRSIII

OK thanks all. I guess the reason that the other one didn't have this was that it was cast perfectly and didn't require balancing?

Hey, I know this is an older post but glad I found it as I am installing 2 zimmerman rotors on my 84 and noticed the same marks in mine.
I figured they were for balancing but this post confirms it.
Would it be too difficult for them to slip a piece of paper into the box to let us know that this is done for balancing??

[mepstein]

Originally Posted by seafood10

Hey, I know this is an older post but glad I found it as I am installing 2 zimmerman rotors on my 84 and noticed the same marks in mine.
I figured they were for balancing but this post confirms it.
Would it be too difficult for them to slip a piece of paper into the box to let us know that this is done for balancing??

That would be unusual. It's just a part made to spec. Most parts don't include an explanation to their manufacture. Maybe on their website but rarely in a box.

[seafood10]

Originally Posted by mepstein

That would be unusual. It's just a part made to spec. Most parts don't include an explanation to their manufacture. Maybe on their website but rarely in a box.

I guess we have not purchased many of the same items then.

[mepstein]

Originally Posted by seafood10

I guess we have not purchased many of the same items then.

I'm mostly familiar with parts that come into our shop from distributors. Probably $10-20K a month. I imagine boutique parts from small manufacturers, custom and consumer oriented retail has more info but your average replacement part (rotors) is just shipped in a box. No instructions

[Tippy]

Originally Posted by JRSIII

OK thanks all. I guess the reason that the other one didn't have this was that it was cast perfectly and didn't require balancing?

Cast perfect is probably an oxymoron, hence the balance notches you saw.

[midnight911]

That looks dangerous. I'll take them off your hands. Just send them to me.

[GaryR]

I would be more concerned with the special "these rotors are defective, do not use" codes on there!

[Fleming]

Has anyone measured the width of the machined divot?

Confirm or deny if it is the wear limit to minimum rotor thickness.

I've been told it is the rotor thickness "visual check". Is this true?

[JRSIII]

That would make a heck of a lot of sense. Much like a tell tale holes in chemical plant / refinery piping. But only one of the two rotors I ordered had this.

[sugarwood]

Oh funny, I always thought it was a "wear bar" like on tires.

[old man neri]

Here my two old rotors. I just measured them. A hair under 20mm.

[gtc]

The pads don't usually wear all the way to the edge of the rotor, so the grooves wouldn't be too useful as wear indicators.

[donporfi]

All rotating parts need to be balanced to avoid vibration.
To correct unbalance you add weight like when balancing wheel and tire assemblies or remove weight like in this case where they milled the rotor.
Sometimes the unbalance falls between a tolerance of the balance quality grade and you do not need to do any correction, that is why JRSIII does not see this milled part in one of the rotors he received.
Other parts where you will see milled parts or drilled parts to correct unbalance are flywheels, electric motor rotors, crankshafts, con rods, fans etc.

[djpateman]

I used to see heavy pieces of wire used for balancing.

[Tippy]

Thank you for using the proper term, unbalance. Imbalance is generally incorrectly used instead.