Hi guys, My son has a 94 RX7 see pic... Anyway, it was recently rebuilt
and dynoed at 387hp but after it warmed up they were seeing a drop off
in compression... So, they tore the engine back down and did three
things... 1st they verified the oil meeting was ok... It was.  Then they
verified all the clearances which led they to think that the 3mm apex
seals were sticking because the clearances were on the "Tight" side.
Here was the reasoning... They thought that the rotors may have been
machined wrong and when the engine heats up that the rotor is expanding
just a little and pinching the seals not allowing them to slid properly
and thus allowing some blow by. Well the re-Machined the rotors put the
engine back together and guess what... It Ran fine until it heated up
then lost compression and quit.  So it is coming back out again for
another tear down... Has anyone ever seen this before or have any ideas?
Oh, also the reason it was originally rebuilt was because it lost
compression... New rotor housings, seals, bearings etc... The only Idea
I have now is to have them replace the Rotors.  Help!


Mike C.

When the rotor expands due to heat the slots get slightly larger.

The side seals could be sticking. There is an end clearance spec on the side seals.

3 mm apex seals means they are after market apex seals. That means after market apex seal
springs. The seal slots run very very hot so the apex seal spring heat treat if any
could be going away. Check the spring height before and after. It is also a good idea
to check the spring rate but that is much harder to do. There are tools out there
for checking the spring rate on valve springs but they are not much good
for apex seal springs. The material the springs are made from is critical.

Another possibility is stock apex seals have a crown. Place them belly to belly
and you can see it. Check your after market apex seals for crown. If no crown
you have bad apex seals. The crown handles heat distortion in the rotor housing
when it warms up.

http://www.rotaryeng.net/seals.html

Mix 2 cycle oil with the fuel. One ounce per gallon of gas.


What brand of apex seals are these?

-- 
Paul Lamar ...No rotor no motor.

Mike C,
I just recently had my RX8 rotor cut for 3mm seals. The depth shouldn't be a
problem the depth is 9.8mm, some use 10mm. If it's too deep this reduces the
spring preload.  I didn't think of the springs but Paul covered that. The
clearances between apex seal and the sides of the apex seal slots are
covered in the workshop manual ( I can't remember the clearance). So as long
as all those things meet spec you should be OK. I'm pretty sure they should
have check the side clearance at the time of rebuild - ask them.
In conclusion I think it might be either the apex seals are sticking because
of lack of clearance with the recut being too tight when hot, or the springs
being too soft when hot( faulty springs) or slot too deep.
George ( down under)

Also there is another factor but it should show up right away.
If the slot was down in a mill with a 3 mm cutter the surface
finish of the walls of the slot are less than ideal. It should be done with
a grinder or broached. The surface finish on these slots is critical.