Sender: <marv@lancaironline.net> (Marvin Kaye)
To: flyrotary
Date: Sun, 23 Feb 2003 12:17:47 -0500
Message-ID: <redirect-2034764@logan.com>
From: "Ed Anderson" <eanderson@carolina.rr.com>
Subject: Thermal Pellet in Eccentric Shaft
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Although most folks are probably aware of this, due to the potential for
engine damage, I thought I would pass this on to the list.

An individual flying with a rotary and I were having a discussion when the
subject of the thermal pellet in the eccentric shaft came up.

In a discussion of the possible reason that the "rubber" apex corner seals
had melted and disappeared from one of his rotors, it became clear that my
friend had misunderstood what action he was to take to disable the thermal
pellet.  Since, if done incorrectly this could cause your rotors to overheat
and cause damage, I thought I would mention the process again.

The thermal pellet is designed to drain oil from the eccentric shaft to the
oil sump when the engine is cold (enabling a rapid heating of the rotors,
apparently there for emission purposes), this drain precludes cooling oil
from initially being sprayed inside the rotors.  After the engine oil warms
up, the thermal pellet closes the drain hole and  cooling oil is now sprayed
inside the rotors. Since damage to the rotors may result if the pellet fails
to function properly, for aircraft use the pellet is usually either
1).disabled or 2.) removed and replaced with a metal plug.

1.) To disable the thermal pellet, you need to insert a tubular (yes! it
must be hollow) spacer approx 5/16" long into the pulley bolt recess for the
thermal pellet (see description in Tracy Crook's conversion manual). The
5/16" long spacer pushes the thermal pellet back far enough to close off the
drain hole.  The reason the spacer has to be hollow is that when the pellet
warms up a pin is pushed out of the small end of the thermal pellet (the end
toward the pulley bolt), if the spacer is solid rather than hollow, this pin
will push against the spacer causing the thermal pellet to be pushed even
further toward the rear and possibly uncover the drain hole from the
opposite direction.  My friend used a solid spacer resulting in some cooling
oil draining into the oil sump rather than spraying inside the rotor.  This
caused his rotor to overheat and ended up melting his "rubber" corner seals
and reducing his compression and power.

2). You can completely replace the thermal pellet with a metal plug (sold by
Dave Atkins and MAzdatrix, I believe Bruce Turrentine installs them in his
rebuilds for aircraft use - but check with him).  The cost is around $15 for
the metal plug which is inserted per their directions keeping only the
larger spring from the thermal pellet configuration.  This metal plug keeps
the drain hole permanently closed and cooling oil continously sprayed inside
the rotors..

Either system will work (if done properly), I used the tubular spacer on my
first engine and the metal plug route on my second engine. If done
incorrectly then rotor overheat and damage can occur.

FWIW

Ed Anderson

 Matthews, NC
RV-6A N494BW
eanderson@carolina.rr.com