Paul,I am using a 3.25"  diameter prop shaft on my PSRU  and the oil
seal is at its maximum RPM limit for recirculating oil and would be over
the limit for grease.  It has a wiper and a built in  oil reservoir
between the sealing surfaces.   What will you be using on the 5.10"
diameter shaft running at propeller speeds? I had considered a slinger
but  any circumstance that lowers the nose would make a mess and
contaminate ground water.  I would be interested in a link to a
supplier that sells something for high speed large diameter shafts.
George grimes

The Ceramic bearings are sealed (I think. I hope :)) and are rated
for 14,000 RPM.

Paul Lamar

I requested quotes for open bearings only because they spec higher for
durability and rpm. They will have no seals. Gear lube and a pump is
what is on order here. The lube may work well without a pump as the
bearings can run totally dry for some time, and there will always be
lube in the tube housing anyway.

I looked at a couple sources for seals for the prop end. There are
plenty of options available. We need to create something to hold the
seal within the prop end housing cap, while holding the bearing in
place.

Ed Carver

High speed seals are rated in psi-fpm.
The best are graphite reinforced PTFE ...AKA Teflon.
Max number for oil is 520,000 psi-fpm.
In other words at 100 psi the surface speed can be 5200 feet per
minute max. If the shaft is 1 foot in circumference that is 5200 RPM.

Of course the sealed ceramic ball bearings have no where near that
pressure on the seal. Lets say it is ten psi as a wild ass guess. So
max RPM would be 52,000 for a one foot circumference shaft. Our
shaft is 4.25 inches (not 5.1") inches diameter therefor the
circumference is 1.1 foot.

These seals are very expensive. If you are applying full engine oil
pressure to a rotating seal I suggest changing the design so there
is an oil drain back on the outer edge of the plain bearing before
the seal.

The largest McMaster sells is 2.5 inches ID. The price is $73.
So if those ceramic bearings are not sealed we are going to pay
through the nose if we can even find one.

On the Cont. O-470 in my C182 with a 2-3/8" OD shaft dynamic air
pressure getting by the seal pressurizes the crank case and blows
the oil vapor over board without an air oil separator. That is
called a stretch-over oil seal as one must get it past the prop
flange by stretching it. Just inside the seal is an oil drain back
passage to
the crankcase.

Paul Lamar


The seals I saw were much less and were the proper size. Will find them
again shortly online through google. I don't plan on using engine oil to
lube these things.

Ed Carver

Well sealed bearings come with grease that appears to last for years.

Paul Lamar