Mount a small cut off hand grinder on a welded up two inch square
steel tube box frame and mount the rotor on the milling table
with an angle plate.
Cutoff disk width is about .046" so it will fit in the
2 mm original slot with. Cutoff disk are about $4 each so you
can throw them away when they are worn.
2 mm = 0.0788"
3 mm = 0.1182"
So all you need grind off both sides of the slot is 0.0197"
or .5 mm.
I learned this trick from Tracy Crook as he built a Ford sun gear
grinder using his lathe and a bench grinder.
When you get this built let me know and I will send you a lot
of business :-) You could operate this business out of a closet.
Paul Lamar
Although I have never heard this mentioned before, the apex seal tip
edges where they intersect the flat faces of the late model rew rotors
are hardened after the grove is cut in the factory. Milling them out
from 2mm to 3 mm may eliminate the edge surface hardening and lead to
cracking of the grove edges. This was adopted from the S-2 racing series
engine development. Not sure if this process was done on any earlier
engines, FWIW.........
Also I cannot recall an instance where the racing rotaries in the
factory program ever used 3mm seals. They used a bunch of different apex
seal materials and arrangements, tho.....
Here is another interesting factoid; the steel cast-in insert on the
housings is called SIP (Sheet-metal Insert Process) and after it is in,
the metal is plated with a porous chrome plating process called
MCP-Micro Channel Plating (which seems to me very similar to chrome
channel plating used in aircraft cylinders sometimes) for lubrication
purposes. This begs the question-Why not send them out to be replated
with channel chome at a cylinder shop if they are scratched or worn? In
any case, then the surface was sprayed with Teflon (to assist bedding in
of the apex seals) on the 2nd gen turbo, but that coating was switched
to baked carbon graphite in the REW 3rd gen engines. A few other
sophisticated improvements were made in the 3rd gen engines (eliminating
rotor lean at high power output [a new million dollar tool was bought to
machine the parts to the new clearances], rotor bearing oil supply,
upping the oil pressure by 60%, Hitachi HT-12s with 9 blades instead of
10 on turbine, etc).
Lest you think I just know all this minutia off the top of my head, you
too can read all about it in the very professional book "RX7" by Jack K
Yamaguchi and John Dinkel (a real great book for rx7 3rd gen owners,
which focuses on the evolutionary development of the 3rd gen from the
other gens, with lots of tech details and background info) that I got
for free (Ha) by buying so many FD parts from a Mazda dealership in
Houston.
Marc Wiese
3 mm steel seals tend to jump off the hump at super high speeds.
That is why they are not used in racing engines.
Since we limit our RPM to about 7500 with a 2.85:1 PSRU
and 6500 RPM with a 2.17:1 PSRU jumping off the hump is not
a problem. What is a problem is the shattering of the
2 mm stock seals with as little as one ping or detonation
common with turbo charged engines.
Further more the loads on the edges of the rotor slots
are lower with the two piece seals due to lower leverage forces
as compared to the stock 3 piece seals. I can understand why
the factory might be hardening the area around the apex
seal slots on the rotors.
Some of the racers use the much lighter weight but much more
expensive 3 mm ceramic seals and run at super high speeds.
Since there is no center main bearing the e-shaft will bend
due to high pressures in the combustion chamber or super high
RPM centrifugal forces therefore the rotors will indeed lean.
Now perhaps what that machine really does is make the side face
of the rotor slightly cone shaped to accommodate the inevitable
lean at super high RPM.
Here is a picture of a two rotor engine with a center main bearing.
Paul Lamar
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