Chapter 23 – EGTs on deck!

Today was primarily about getting the exhaust pipe EGT probes positioned and installed, but first I pulled the peel ply off the bottom cowl left side outboard exhaust pipe clearance depression 2-ply CF layup.  It looked great, so I moved to the inside…

Where I pulled the peel ply on the inside of the divot that I created on the left side of the bottom cowling for the #3 cylinder exhaust pipe clearance (I forgot to grab any pics of the ensuing 1-ply CF layup and peel ply on the inside bottom cowling, but you can catch glimpses of it in the pics of the cylinder #3 exhaust pipe EGT probe immediately below).

I spent well over 2 hours in my final research on EGT probe position (facing inboard or outboard?), placement (how far from exhaust pipe flange?) and any other general tips and/or tricks that I could find.

If possible, EGT probes should all be equidistant from their respective exhaust pipe mounting flanges to all be reporting their equivalent heat value at the same distance from the heat source (aka “the exhaust port’).  Makes sense.  That being said, I also noted the oft warning of having the EGT probes mounted too close to the exhaust flange/port and risk literally getting burned up, drastically reducing probe life.  The sweet spot reportedly is around a 3″ EGT probe position from the exhaust mounting flange, which is inline with GRT’s recommendation of 2-8″ as denoted in their EIS install manual.

It took a good half hour to find a compromised sweet spot between all the exhaust pipes, the aft cylinders being the odd ones out requiring special attention here.  The common EGT probe install position/distance I settled on for all cylinder exhaust pipes was 2.65″ from exhaust flange face to EGT probe hole.  For added measure I’ll throw in a swag of +/- 0.15″ max… but probably more like +/- 0.07″ in reality.

Here we have the left outboard/cylinder #3 exhaust pipe EGT probe hole drilled (pic 1) and installed (pic 2).

And here on the right side, we have the inboard/aft cylinder #2 exhaust pipe EGT probe hole drilled, with the EGT probe installed on the outboard/forward cylinder #4 exhaust pipe.

Here I’ll quickly note another oft-cited warning that various homebuilders provided: ensure not to block access to installing or removing the bottom spark plugs.  Yes, good thing to watch for!

Again, the aft cylinders needed some special consideration not just in the distance between the exhaust pipe flange and the EGT probe, but also in the clocking of the probe —which I really haven’t touched on yet, but was a significant consideration for each individual probe— not only in regards to what angle the EGT probe body was protruding from the exhaust pipe, but specifically the placement of the securing hose clamp screw assembly.

A perfect example of what I’m talking about is the right inboard/cylinder #2 exhaust pipe: if the hose clamp screw assembly is positioned forward, approximately 90° from the EGT probe (as they all are; standard position) as in pic 1, then it results in diminished clearance for that exhaust pipe as a whole with the bottom cowling as you can see in pic 2.  Since I have just a hair under a 1/2″ worth of clearance between cylinder #2’s exhaust pipe and the bottom cowling, clearly the hose clamp screw assembly in this position diminishes that clearance greatly and is an outright no-go.

The problem then potentially becomes about as much of a pain in the keister as well if I place the hose clamp screw assembly 90° out on the other (aft) side, since it starts clogging up the access to remove or install the #2 cylinder bottom spark plug [Ah, which I was warned to watch out for!].  But I will note that I didn’t test out this possible clearance issue, but will tomorrow….

Yep, I jumped the gun on checking clearance for the left inboard/cylinder #1 exhaust pipe EGT probe by mounting the bottom cowling in place, so again I’ll have to check spark plug removal/install clearance on cylinder #2 tomorrow.

That being said, here we have the EGT probes installed on the right side exhaust pipes.

One last note on the possible clearance issue with cylinder #2 spark plug removal/install and the exhaust pipe EGT probe hose clamp screw assembly… IF that proves to be an issue the fix would be installing a compression fitting style EGT probe.  That would require welding in a threaded port at the EGT probe position on the exhaust pipe, then sliding the EGT probe in position and threading in a securing cap that is pre-installed around the EGT probe assembly.   I would of course need to order this type of EGT probe from GRT:

Additionally, if possible I wanted each cylinder exhaust pipe EGT probe to face inboard towards the engine to allow for better routing of the EGT probe wires.  Being very low voltage signal wires I wanted these EGT probe wires as far away and not comingling with the much higher powered spark plug wires in any fashion.  However, I was only able to face the #1 cylinder exhaust pipe (aft left) EGT probe inward, with all the remaining facing outboard.

And as it just so happens, the final EGT probe I installed was on cylinder #1.  Again, I didn’t want the EGT probe hose clamp screw assembly facing downward since this would eat up exhaust pipe clearance with the bottom cowling.  On the top side I didn’t want the hose clamp screw assembly too canted inboard since I didn’t want any ensuing clearance issues with the cylinder fin baffles that will go in this area.  In short, I wanted the EGT probe hose clamp screw assembly situated squarely on top of the exhaust pipe, with the EGT probe itself facing inboard and positioned slightly downward… pretty much just like it’s shown here:

Here we have the EGT probes mounted into the left side exhaust pipes.

Finally, as I prepared to close up the shop for the evening, I went ahead and set the top cowling in place to check out the positioning of the left exhaust pipes in the aft cowling opening.  Pretty not bad IMO!  The pipes of course need to be trimmed in length and their final openings will both be about 1/2″ inboard (right in pic).

And with that, I called it a night!

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.