From: ReganRanch@aol.com
Message-ID: <77f363ba.35f15bf0@aol.com>
Date: Sat, 5 Sep 1998 11:42:40 EDT
To: lancair.list@olsusa.com
Subject: Caveat Emptor
Mime-Version: 1.0

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In a message dated 98-09-05 00:27:18 EDT, Guy writes about Dans prop
adventure:

<< You should get the old bearings back when you pick up your
 prop. Take them to a bearing house like King Bearing and price them
 directly. It's a rare bearing that is unique to one product. >>

Don't bother. The bearings used in the MT props are proprietary. The
likelihood that a worn bearing would cause a grease leak is minimal. This is
because of the design of the MT hub. The propeller is assembled to the hub by
inserting the blunt end (ferrule) of the blade into the hub past its normal
position. A split angular contact bearing race is installed into a groove in
the ferrule and individual balls and spacers are packed into the race with
grease. When in its normal position, the blade is retained by the balls. A
large snapring, visible from the outside, in conjunction with a fitted plastic
spacer, hold the bearing tight when the engines ON-OFF switch is in the OFF
position. When the engine is making noise, centripetal force loads the
bearings. A single O-ring keeps the grease in the hub and water out.

SO how is it that a bad bearing can cause a grease "leak"? Any bearing wear
would manifest other symptoms like uncontrollable prop RPM or excessive blade
rock (>1/8 inch). If the hub or ferrule were out of tolerance they would have
replaced them. No, the simple answer is that Dan experienced a normal
phenomenon, described it as a "leak" to the prop shop who "fixed" it by
lightening Dan's wallet to the tune of $1,600.

Normal phenomenon? Yes, when the hub is assembled grease is used liberally in
the process and the O-ring is not a perfect seal. During the first hours of
operation it is normal for the grease that ended up in the O-ring grove to
migrate out onto the blade. Later in life, environmental and operational
"events" will allow a small quantity of grease to escape. 

USE COMMON (uncommon?) SENSE. If you see grease on the blade root, investigate
it. Check blade rock and monitor the performance of the constant speed system.
If everything is normal then wipe off the grease and fly on. If the leak is
persistent or copious then replacing the O-ring (a $2 part) on that blade may
be in order.

In general, remember that the aircraft repair business is like any other and
has its share of practitioners that are quick to replace serviceable parts.
Let the shop know in advance that you will want to be there for the tear down
and inspection and that you will want to know why the manufacturer required
that part to be replaced.

Early MT 3 blade props are part compatable with McCaulley props. The basic
design of the MT is good, IMHO.

Regards
Brent