the stock size for rotor apex seals is 2mm right not the 3mm right i have never heard which is which

 

yes stock is the 2mm

 

The stock size for FC's is 2mm. 3mm seals were standard on earlier engines like the 13b from the GSL-SE.

 

i have a 86 na so it would be 2mm right

 

yes.

 

Why were 3mm seals used in the first place OR why were the seals changed?

 

The 3mm seals wear down the rotor housings faster, so when they went with the 13b in the 86+, they put the 2mm. I believe they even tried a 6mm apex seal in one of the earlier engines.. Someone I'm sure has a more elaborate answer then me.

 

6mm thats ridiculous haha. does the 3mm wear the housing faster just because theres is more surface area rubbing the housing or is there another reason?

 

Education, education, education!

The twin dizzy 12A (the true 12A) was fitted with 6mm Carbon-alloy compound apex seals, as found in the RX2 and RX3 pre late 1973.

I know because I have one in my 1971 series 1 RX2. It also has twin side seals on the rotors and no REAPS or emissions gear on the exhaust.

The Mazda part number for the 6mm carbob apex seals was 0839-23-131.

 

You can use 3mm if your grooves are too worn out to accept 2mm or for a few other reasons. I forget, but 3+mm carbon seals might be part of a slew of things necessary for high rpms. You machine out the grooves even further to fit in the 3mm seals. But in general, for common road use, 2mm is better.