Paul and group,

I have Tracy's EM2 installed in my Bush Caddy, and need to install two CHT
thermocouples. I purchased two under the plug thermocouples, but don't have
enough room for the thermocouples to clear the spark plug and the rotor
casting.  Does anyone know how much rotor material is around the trailing
plug  in the area just under the plug?  My thought is to grind out a small
portion of material, 3/16"
wide at a 45 deg. angle with a die grinder just under the plug to
give me enough clearance for the thermocouple wires.   I have
attached photo's to illustrate what I would like to do.  The photo
(0164) with the black marker is where I would like to remove a little
material.  I'm worried about grinding into the water jacket.

I have seen the photo's of the drilled hole in the rotor for placement of a
thermocouple some people have done, but that looks like it is something that
needs to be done with the rotor in a drill press, and not free hand.  My
engine is installed in my aircraft.
Thanks for any advice and comments.

Bob Forbes

Upstate NY

N164WF

There is quite a bit of material there so a bit of die grinding should not
hurt. The internal fins are not necessary in case you were wondering :)

Paul Lamar



I would think it would be better to install under the leading plugs as the
heat is higher there. It would give a better and quicker temp reading. Temp
readings do not change quickly in the metal on the outside of the housing,
but reading at the trailing plug will give an extra delay.

Dale Davies


Paul,

How much good will the TC under the plug actually do as there is a water
jacket between the combustion chamber and the outer housing surface.  Seems
that you will only be reading the coolant temp, not the actual CHT.  Someone
needs to come up with a dril jig so that the 1/8" TC hole can be safely
drilled without having to disassemble the engine.

Mark S.

Not much. Better than nothing :)

The drill jig would be easy to make as it can bolt to the lower (Leading)
spark plug hole. Good idea Mark.

Paul Lamar

Thanks for the responses.  What a great idea for a drill jig application.
The TC holes could be drilled with the engine installed.

As I understand that if I use the TC under the spark plug the temp. reading
will not be very accurate as too what the real time CHT will be, so what if
I were to bolt the spark plug TC too the threaded raised boss just above the
trailing plugs? Thoughts?   Photo attached.

Bob Forbes

That is not the best place for a CHT. The lower spark hole has the highest
metal temperatures and you need to know what they are. 500 F is getting
to be the limit just like an aircraft engine cylinder head.
The place where Mark S installed his is the best place.
You drill down until the drill tip gets steel particles
on the tip. Then you know you are down within 1 mm of the
chrome wear surface.

If you have a drill jig made make 2!  I will buy one.

As I recall the highest temperature Mark S has seen so far is 400F.

Paul Lamar