Heres something i found. I took apart my s4 13bt, only to find that it has 2 mismatched rotors... 1 E and 1 B. Now this defeats the 1 or even 2 letter rule. Also, I havent been able to find anywhere in the FSM that states anything regarding the rotor weights. Lastly, if they truly were so important, why isnt there different part numbers for the different letter rotors?

What are your thoughts on this?

Im sure someone has built a "mis-matched" motor w/o balancing

 

They are not mismatched.
The "E" that you saw is actually a backwards "yo" - katakana Japanese.

The actually rotor weight stamp is something else...not "E".


-Ted

 

so nice of your rotors to greet you with "yo" when you crack open your block... :P

 

Never heard that before...So what/where is the true rotor weight stamp?

 

Im pretty sure you been mistaken, check over your rotors again you might find a different letter. Its happend before and it will again.

 

no no, i've checked over the rotors, im definatly correct... Both letters located in same place of rotor, and as described by others on the forum...

 

Someone post a pic so everyone will all be on the same page with this.

 

Heres a picture i found on the forum

 

The weights are not absolute. I weigh most of mine on a digital scale. The A is generally heaviest of a given type of rotor, while E is the lightest. However...I have seen B's that weigh the same as D's. I've also weighed a bunch of C's in a row (the most common letter) and gotten almost exactly the same weight, and then weighed a B that was lighter than all of those C's that I just weighed. I've had times were E's and D's weighed the same.

Every once in a while I see a rotor marked "CE" or "BE"...both letters right beside each other, but not necessarily aligned as if you wrote them side by side. This is where the japanese comes into play...they just happened to stamp the "C" or whatever right beside the "m" japanese symbol. They always weigh whatever the first letter is..."C" or whatever it is.

So again it is not absolute.

 

well, depending on how much those weight categories differ it might be possible for wear and tear of use to account for the weight differences noted when checking used rotors...

 

Wear and tear of use? Rotors don't wear. They don't touch any surface...they float. Bearing wear can't account for the difference, as that's only a few grams at most. The rotor tips where the apex seals slide do "v" out slightly but again this is only a few grams difference...maybe 0.02 or 0.04lb. Rotor weights can vary by 0.2lb.

 

like I said I wasn't sure how much the categories differed, so now I know that that isn't a cause.

I can say with certainty though that all weight recordings from the SAME SCALE should be precise in relation to one another. My guess is that the stamped rotors were either weighed on different scales (thus, one or both scales could be incorrect), someone made a mistake, or both.

 

Or its the way things are. I weighed two "D" weight S5 rotors after washing the oil out of them when I tore down my J-spec over two years ago.

Weighed them on my paint mixing scale (which is accurate to the 10th of a gram) and came up with 2.1 gram difference between the two.

Same scale, calibrated yearly, within minutes of one another, same weight stamp rotor.

Edit: My experience is with only this one pair of rotors, so I dunno how near or far my findings are from the norm. But thats what I found.

 

for one, I'm sure the weight stamp doesn't mean "this rotor weighs EXACTLY x", I would imagine it's supposed to denote that rotor is within a certain range of values for the weight. secondly, a normal sized paperclip weighs near a gram. that said, 2.1 grams is not very much metal compared to all the metal in a rotor.

 

there will be some weight discrepancy, that's just based on an imperfect manufacturing process, but there is a certain tolerance of error that is acceptable.
Mazda apparently went to a new improved manufacturing process for rotors for the Renesis, so i would be willing to bet you would see less discrepancy with those.

back to what JIMMY54 was asking though, are rotors supposed to have some sort of matched marking on them?

 

they probably grade a batch of rotors at once, so the letters would maybe apply to that production lot number

 

the difference was 2.1g, that wasnt the weight of the rotor

 

Exactly,

We never rebuild any type of engine w/o balancing, benefits far outweigh the low cost...