I replaced the broken, worn out gascolator on Saturday afternoon, and went back Saturday night (living that legendary rock star lifestyle, I am!) to prepare for Sunday's installation of the new EGT gauge. Sometime between finishing the gascolator and returning for the preliminary EGT work, my favorite A&P had stopped by and installed the plug to seal up the gaping hole in the carburetor. While in the eyes of the FAA it would be perfectly allowable for me to have done this myself, there are some things that I feel are better left to the professionals. Drilling and tapping a hole in the carburetor fits firmly in the "have someone smarter do it" category.
The fact that drilling and tapping were required in the first place indicates to me that this plug had never been in there, and that the carb has been sucking air through that hole for at least the last few years. I strongly suspect that this will resolve the slightly rough running engine that I get at around 1400 RPM. That will be nice because 1400 RPM is a power range used almost exclusively during the turn from base leg to final while landing, which is most assuredly not a time when you want anything but a smoooooth running engine. Disconcerting, to say the least, to be low and slow and have even the most minute distrust in your engine. Easily avoided, once you know to expect it, and not really even a problem if you just slog through it, but nice to have it fixed none the less.
The simplest part of the EGT installation looked to be the actual placement of the instrument in the panel, so naturally I saved that part for myself. Four screws, and there it was:
I actually had the foresight (yeah, I'm surprised too!) to write down the color of each of the wires on the wiring harness and which wire of each of the probes that was intended to be attached to it:
Everything else was laid out and ready to go so Co-pilot Rick and I would be able to hit the ground running in the morning:
We agreed that the hardest part of the entire installation would be the process of getting the four probe wires through the firewall and back to the instrument in the panel. Not only would a hole have to be drilled in the firewall, but a shield would have to be put in place to keep the nasty stuff that goes on in the engine compartment where it all belongs: in the engine compartment. It would also be necessary to cushion the bare edges of the hole to keep the probe wires from chafing. To hold the firewall shield in place, two nutplates would have to be installed for the screws to screw into.
Sounds easy, but the cockpit side of the firewall is extremely hard to get at. To rivet the nutplates in place, we would be using blind rivets (which, as opposed to solid, driven rivets which require access to both sides of the surface, can be installed from just one side). Sort of. Someone still has to crawl up under the panel to hold the nutplates in place with the rivets are pushed through the holes. But, the first order of business is to create the holes:
The holes were pretty easily drilled, but we wanted the firewall side of the rivets to be flush with the firewall, so the holes needed to be dimpled. This is done using the same rivet puller that is used to install the rivets, but with the addition of a nifty pair of thingys that create the dimple. This operation requires that there be a person on each side of the firewall. One outside, comfortably standing on a step stool, and another on his back, scrunched up behind the panel, twisted into an ungainly and very uncomfortable position to reach up to the back of the firewall to hold the thingy in place.
You know that guy who asks you to help you move, and when you show up he points at a 100 lb. box for you to pick up, and says "I'll hold the door?" The guy that always manages to face frontward while you pray for your life as you carefully tread backwards down the steep stairs carrying his sofa? Well, he's also the guy that will choose to stand on the step stool, and in this case, that person is me. I swear, I'm like the guy (Marlin Perkins?) in the old TV show (I think it was 'Wild Kingdom,' sponsored by Mutual of Omaha): "I wait in the Jeep while Jim approaches the rabid, PMS-enraged Lioness." Co-pilot Rick ended up on the floor of the cockpit with various pieces/parts of the floor leaving semi-permanent indentations in his back. I stood on the stool. But... we got it done:
Once the holes were dimpled and de-burred, Rick dove in again to hold the nutplates in place while I pulled the blind rivets:
To get a large enough diameter hole in the firewall, we had to resort to the Unibit. Using a Unibit is a lot like working with fiberglass: the good news is that it can drill a hole very quickly. The bad news is, of course, that it can drill a hole very quickly:
After a second trip to the Aviation Parts Department at the local Lowe's, we were able to install a large enough grommet:
With the portal through the firewall finally being done, it was on to the much easier task of installing the probes into the exhaust pipes. The specs included with the probes direct that they be installed anywhere from four to eight inches from the exhaust flange, but those suggested specs weren't going to work for my pipes. I had to go a little bit closer than the four inch minimum in order to work around the bent parts of the pipes and the areas where the pipes join and are double thick . The good news, though, was that the unaffordium drill bits made short work of the task. I didn't even need the second one that I had bought:
The installation of the probes is very simple. Stick them in the hole, and tighten the hose clamp:
Trim off the excess length of the hose clamps:
We secured the cables to other parts of the engine in order to keep them from floating around in there getting themselves into trouble:
Then it's through the firewall and attached to the wiring harness, yet another job that required someone to crawl up behind the panel. I waited in the Jeep:
Me and Marlin Perkins: we're all about the glory, so I got out of the Jeep and did the test run to see if everything was working. All four probes worked:
I'm a little worried about the indicated temps, though. Pretty high for a mere 1500 RPM! What are they going to be like at full throttle?? This is, of course, the result of placing them too close to the exhaust flanges. Rick thinks it might be ok in flight, though, since there will be cooling air blowing across the pipes. He's probably right, but I reserve the right to stew about it until I find out.
My nice, neat work table was showing the results of the intense installation activity, so it was time to get stuff thrown away or put away:
The final step was to use heat resistant RTV goop to stain my clothes and to keep the nasty stuff on the right side of the firewall:
All done! The plane just needs to be buttoned up and have the annual signed off and we're ready to go! Oh, and it was Wild Kingdom.