Ed Anderson wrote:

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 apparently

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 and perhaps others, 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.  Of

course,

you

could

take your chances and simply leave the pellet in its stock

configuration,

but given the possiblity for damage if it fails...........

FWIW

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

All correct as far as I know.   I would add the following points.

You

can

use the solid spacers *IF* you pull the pin out of the thermal

pellet.

I

was afraid this would allow the working fluid (wax) to escape the

pellet

but

apparently there is a piston inside which prevents this.  The length

of

the

spacer inserted into the shaft bolt to disable is dependant on

whether

you

use the stock or aftermarket aluminum pulley.  It needs to be

slightly

longer with the aftermarket pulley.  I'll try & lookup the exact

dimensions.

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

Mark wrote:

Thanks for penning this article Ed, I have uploaded it and Tracy's

comments

to the best practises site. Tracy I'll add those dimensions if you can

find

them.

Mark Wrathall
http://members.aon.at/wrathall/rotary/

OK Mark, here's the measurements on the spacers.  Use .400" if using the
stock pulley and .600" if using the aftermarket part.

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

 
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