So I have been reading up on the engine in prep for my coming rebuild. I've also have the Mazdatrix DVD, etc...

Everything makes sense design-wise but I am confused why the apex seals are designed to have one corner break off basically (2 piece design). Why aren't the apex seals just measured and clearanced like the side seals? Also, I know some place sell 1 piece seals anyhow.

So long question short, why is the apex seal designed to run that corner separate, and not one long seal?

Ease my curiosity!!

 

It seals a bit better - lets the spring not only push it out against the rotor housing, but push sideways against the side housings. Bridgeports past a certain size need to go back to 1 piece seals so the little corner piece doesn't get eaten by a port.

 

1 piece apex seals are used for racing.

The main issue is that the apex seal operates at a high temperature from friction at high rpm and so it has to be short enough to allow it to grow with thermal expansion so it doesn't get stuck between the side housings.

Then, when the apex seal is cooler it is short and there are gaps at the ends so it does not seal as well.

Ceramic has a low coefficient of thermal expansion so 1 piece ceramic seals can be run with a pretty tight end clearance. Same with Carbon/Aluminum seals. 1 piece steel seals are another story though.

 

Thank you, that makes sense. Do the side seals just not see that same amount of temperature variation then? Presumably because they aren't in path of combustion as direct as the apexes are?