Mazda has gone back to a 2-piece, 2mm apex seal design recently; this replaces
the original 3-piece, 2mm apex seal. These apex seals are fine for most
applications, even high horsepower applications. Racers have used these
stock seals in engines that boost over 20psi and produce around 500hp!
The key is to prevent detonation.
The older apex seal had an "electron beam hardened" leading edge, which K2RD had
tested to be around 60C Brinnell hardness; the back end of the apex seal tested a
softer 40C Brinnell hardness. The harder leading edge allows for longer apex
seal life, while the softer back end is easier on the apex seal groove in the rotor.
Excessive apex seal hardness can cause premature apex seal groove wear in the rotor.
If you want more safety from detonation, you can use 3mm apex seals, but
it's really unnecessary if you keep detonation in check. Rotors need to be
milled to accept the larger 3mm apex seals; it's tricky to mill rotors
accurately so they have the correct clearances. Too much clearance and you
induce too much blow-by and excessive apex seal travel. Too little clearance
and you risk apex seal binding in the groove.
Recently, there have been aftermarket apex seals being offered by several vendors.
These aftermarket apex seals are priced cheaper than the stock OEM Mazda units and
are a very attractive option to the Mazda OEM stuff. Initial longevity reports
have started to trickle in, and they do not sound promising. Due to the softer
materials being used in these aftermarket apex seals, apex seal failure rises.
Some vendors even tout their aftermarket apex seals cause no rotor housing damage
when they do fail! While this might sound like a good deal, any apex seal
failure will require a rebuild! Engine rebuilds are time-consuming and costs
Hurley Engineering of U.K. was one of the first economical options over the stock
Mazda OEM units. Keep in mind that stock Mazda OEM apex seals were priced over
$40 / each, and a set of six was approaching $300; current Mazda prices around $50 /
each or more. Hurley Engineering had their set of six apex seals for around $200,
which made it an attractive option. Hurley Engineering were touting their seals
to break-in quicker and cause very little damage when they failed. Most user
experiences are consistent with their claims. Now, this may sound like a good
thing, but upon closer examination of these seals, this is not the case. We
theorize that the Hurley Engineering apex seals are made of softer metal / steel.
This would explain the Hurley Engineering claims. Early engine failures seem
to abound with these apex seals, and even though you end up with no or very little
damage, I don't call doing early rebuilds an advantage.
Atkins is another vendors who is offering their version of a 2mm apex seal replacement.
Initial experiences seem to imply that these Atkins apex seals are also softer metal.
We have one pic of a failed apex seal that looks to be caused by a non-chamfered exhaust
port. The Atkins apex seal splintered upon contact with the sharp edges of the
exhaust port. Priced at $40 each, it is one of the more expensive options, but
the initial evidence of these Atkins apex seals being made of softer metal doesn't
make this a good deal. I would place these Atkins apex seal in almost the same
boat as the Hurley stuff. Atkins does not recommend "high boost" with their units,
and those users who do not run more than 15psi should be okay. This recommendation
seems consistent with trying to use a softer seal.
Rotary Aviation have been touting their "700% stronger" apex seals, but having stronger
apex seals does not necessary mean better. The apex seal looks to be pretty good,
but I question how the harder RA apex seal will do in terms of premature wear on the
rotor housing surface. RA has admitted that their apex seal springs are
inferior to the Mazda OEM units. RA has admitted that their apex seal springs
are not heat treated (Mazda OEM apex seals springs are heat treated.) - no surprise.
RA has also claimed that the stock Mazda OEM apex seal springs have hints of Inconel
(a really strong steel with very high heat resistance properties), which of course the
RA apex seal springs do not have. This explains the higher cost of the Mazda
OEM apex seal springs versus the RA comparable parts. The economical set-up
looks to be to run the RA apex seals with stock Mazda OEM apex seal springs.
Ideally, it looks like Mazda has the best design with the leading edge hardened, and
it seems that none of the aftermarket options can offer a similar design at a cheaper
price; the Mazda OEM apex seals are costly due to the intensive hardening process -
Mazda did do their homework on R&D on their apex seals!
Ianneti offers hyper expensive ceramic apex seals in both 2mm and 3mm size.
A set of six ceramic apex seals can easily break US$1,000!
We had a feeling these aftermarket apex seals were not as
good as the stock factory Mazda apex seals.  Mazda hardens the tips, so they
have better wear resistance.  The stronger tip sections also help them
against the hot combustion process.  The stock Mazda apex seals are otherwise
cast steel.  These other alternative apex seals look like they are cast
steel with no hardening at the tips; this would explain the cheap prices.
These don't seem to last as long versus the stock Mazda apex seals.
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