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


Look to heavy duty diesel engines such as the Cummins 1710 engine for
Teflon seals. Some have the same diameter seal front or rear but the direction
is the opposite. They may be in the $50 range as they are stock items. The
larger engines will have diameters required. A Detroit Diesel 60 series is
close to 3" shaft diameter. 12V and 16V 92 and 149 engines should have larger
seals.

Dale Davies