And why did Mazda stop using them?

They're not really needed. I've never used them. At one point they came affixed to OEM 3mm apex seals. They don't any longer as far as I know.

From my '76 Cosmo FSM:

 

I've never seen this before. My apex seals came glued together. I notice that these drawings have the apex seal without the other end attached. Maybe the assist piece (such a technical name) was there to help slip in the other end of the seal?

 

You mean the 'side piece', as the little triangle things are called in the FSM? Some people call them wedgies. (I don't but you can)

Anyway you'll notice that the rotor gear side is facing down in the illustration. Because this is the front rotor (big F on the face) once you flip it over so the gear side meshes with the stationary gear, the slant part of the apex seals will be facing up ready for the 'side pieces' to be installed. What the assist pieces do in this case is add support under the apex seals so the side pieces can be pushed all the way down into the apex slots so they don't poke out above the rotor or rotor housing. This I assume will keep them from popping out while installing the intermediate plate.

You know how you must lift the eccentric shaft at one point while installing the intermediate plate? The apex side pieces can sometimes jump out and drop down into a water jacket or onto your shoe. that is never a good thing because if you're like me and use RTV on the legs of the housings to seal the sump area, it just takes extra time to reset everything, meanwhile the RTV is curing. If you're like others who use vaseline on the coolant seals, they start to expand and can get pinched as they pooch out and get crushed as the tension bolts are torqued. I switched to wheel bearing grease because you need less of it and use oil (20w50 'cause it's thicker than 10w30 lol) as a prelube because vaseline makes for a lousy assembly lube. It really does.

Yeah, the side pieces can give you a hard time but I've found that you can simply place them into their slots after the springs are fully seated and they will press in as the intermediate (and rear plate) are torqued down. It really works. They don't jump out while the intermediate is getting worked past the shaft because they are not under tension, and there is no need for assist pieces, ever.

Or you can glue your apex seals together and forget about 'em.

 

They are just pieces of carbon to help when you start building the engine. First time you fire it up it burns off.

 

Dude, rubber. They're rubber, dude.

 

Really? I guess thats another reason not to trust a dealership

 

Black rubber, so probably carbon impregnated, like car tires, if that helps.

 

Thanks for clarifying this Jeff, guess they need to update the FSM's (I know they won't haha)

 

You could also go the Pineapple route and use Crisco and a big transfer syringe to apply it.

 

I would never use something that will turn rancid. That's disgusting. lol

 

My understanding is that they are there to aid in seating the apex seal springs. With the advent and more common use of Super Glue, they really aren't needed.