I can't figure how the clearance could be so large on
an essentially new engine.
Here's what I have:
Main Bearing Clearance
Front Rotor 0.0038"
Center Rotor 0.0033"
Rear Rotor 0.0036"
Each of these is above the spec range of 0.0016" - 0.0031"
The rotor bearings are right in there with 0.0022" - 0.0024".
Does this make sense to anybody? Did Mazda provide increased oil
clearance
on these 3 rotor engines? I would really hate to press out the
babbit on
good bearings... I'll probably screw it up if I do.
Any suggestions welcome.
If it was my engine I would just put it back together. The
journals are
long and large in diameter. When I raced a Fiat (yes it has been done)
I ran
.004" on the mains and .0035" on the rods. Ran the same main bearings
for
years. The rods did well but when they get a shine on them I changed
them. I
pay extra for racing bearings that are advertised as being .0005"
oversized.
A little loose is a lot better than too tight. For big bearings extra
clearance would seem the smart move. When we scream the engine the
crank
takes on an "S" shape and shines the ends of the main bearings. It
doesn't
seem to hurt them any. I wipe off the shine with 600 wet or dry paper
in the
cleaning tank. The best RPM my driver has come up with so far is around
11,000. Just run it up to 9,500 RPM in second gear and stick it back
in first
while going for third. Be sure to let the clutch out to be sure its in
first.
It shines the bearings up real nice. It scuffs the corner seals a bit
and the
corners of the rotors drag a bit on the side housings. The engine ran
fine
and finished the weekend.
Aircraft use will be close to a 100% duty cycle. Full throttle for
hours on
end. More stress in many ways then racing will impose.
Lynn E. Hanover
Except when you climb up to 10,000 feet normally aspirated.
Then you are down on power a bit.
Paul Lamar
Is full power at 6000 rpm different from full power at 7000 or 8000 rpm?
Is 200 hp at 6000 rpm different from 200 hp at 7000 rpm as far as engine
stress is concerned? I'm guessing that the 6000 rpm engine will last
longer. Jerry
Yes there is a difference of course.
Well one may last 4000 hours and the other only 3000 hours :-)
I am joking. I don't think anybody knows. My guess, based on what
low apex seal wear Tracy is seeing, is, we are being too conservative with
a 2.17:1 PSRU. I think we can get more power with a better power to weight ratio
if we go to a 2.85:1 gear box and higher RPM. This is not a piston engine.
The centrifugal loads on the rotor bearings are proportional to the square of RPM.
Lets say the engine bearings will live at 10,000 RPM as demonstrated by those racing
rotary engines. At 9000 RPM the loads are
19% less. At 8000 RPM the loads are 36% less. At 7000 RPM the loads
are 51% less. At 6000 RPM the loads are 64% less than they are at 10,000
RPM. I don't think anybody is seeing any problems with the bearings at the RPMs
we are running now.
The other life issue is the rubbing speed of the apex seals. Stock seals
are cheap to replace if the rotors are clean.
Ceramic apex seals will last for 20,000 hours at 3600 RPM
so maybe they will last for 10,000 hours at 7200 RPM.
Paul Lamar
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