I found another engine that somebody had over hauled with Teflon Encapsulated
silicon O-ring that were too large in cross section. The Teflon was extruded into the space between end housing and rotor housing. This was also due to another mistake made by the over hauler.

He/She used some sort of gasket compound between housings. THIS IS A BIG NO NO.
Do not use anything between housings!!! NONE NADA!! The engine is designed to run metal to metal. Let the O-rings do their job. Follow the instructions in the over haul manual precisely. Also the gasket material partially fills the O-ring grooves not allowing the O-rings to expand fully.

The owner of this engine was lucky the silicon did not expand further and crack the end housing. It has happened several times.

The first picture is the O-ring I took out of the engine.

The correct section diameter for the inner slot is .093" maximum and
.080" to be on the safe side. Do NOT use 3/32" as they can be as much as .110"
in diameter. The outer slot is narrower so .080 is a max section diameter.
Mic the new O-rings before you install them to be sure. http://www.creavey.com/

Teflon encapsulated silicone O-rings are great if properly installed. They will tolerate a moderately over heated engine as TES O-rings are good to 500 F and Teflon is inert to all known chemicals unlike silicon alone.

Paul Lamar

Hi Paul;

It is common practice to use a "thin" film of hylomar between the
housings and on the orings to ensure they stay in the groove during
assembly.
A thin film of aviation sealant or similar is used on the legs to seal
the oil pan area.  I do mean "thin".
It has been surmised that too much in the oring groove could result in
hydrolock? causing leakage of the groove wall failure you posted.
Many of the assembly videos specifically recommend hylomar.

The oring failure you posted above is similar to the ones Brian D Cain
posted (an getting grief for posting it, I might add).
Was the break and melted section of the oring between the spark plugs
and exhaust?
Have you measured the relaxed dimensions of these orings?  know the
source?  pre-assembly sizes?

Cheers
~Cary

No the break was in the right place.
Hylomar; Yes but I don't think the shop manual does. I use Vasoline to hold them
in as well as store them on a board for a couple of days. Then they
lie in the groove with no trouble. The petroleum jelly is recommended in the
RX8 engine manual page 01-10-37. Silicone is used to seal the leg area
with a bead diameter of .255 inches max.

Back in my racing days (40 years ago) Hi Lomar was my nick name :)

Paul Lamar