Baffling

Over the weekend I took some time to seal up all of the visible air gaps around the baffling system. To help find and plug the gaps, I put a lead light on top of the engine, then installed the top cowl. I had to reposition the light a few times, but it did a nice job of finding many little gaps that needed to be filled with RTV.

This had to be done at night to ensure the garage was dark enough, but that works well since I’m typically working at night.

Tonight I used RTV to secure the two emag blast tubes. These tubes direct air from the engine compartment onto the magnetos, helping cooling the magnetos during engine operation. I’m contemplating adding a blast tube to the alternator, but I’m concerned about moisture being blasted into the voltage regulator on the back of the alternator. This would be a problem when flying through clouds for example. The alternator is up front, but the emags are at the back of the engine. The emag blast tubes are less susceptible to moisture because of their location, so I’m not worried about them.

Today I riveted the baffle seals into position.

The seals are secured with pop rivets and washers. The washers prevent the rivet head from simply pulling through the rubber.

No problems with the riveting, which was made easier with the snorkel removed.

Today I cut out the baffle seals and clecoed them in place. The seals come in a roll of rubber material, with the shapes pre-punched. It took a little time to cut out each shape with a razor, but it was easy to do. Each part is stamped with a label, and they are installed from part A to M.

The baffle seals press against the top cowling forming a seal, and forcing the airflow down through the cooling fins and into the ducting that cools engine components. Any gaps in the baffle seals means inefficient cooling and higher engine operating temperatures.

Based on some vans Air Force threads, I was ready for some of these seals to need to be switched, or flipped, or something. What I found was that if installed with the labels facing outside, everything fit just right. Except for part A, which appeared to be reversed. After a bit of deliberation, I decided it fit best with the label facing inwards. Once I have the cowling on, I guess I’ll find out!

Tonight I shaped the left hand air ramp. This was trickier than the right hand side because the ramp is part of the air filter cover. Bending the ramp risks damaging or bending the cover. I practiced on a piece of scrap, and when that came out almost perfect I got started with the real piece. The first bend went well, and the second was going well also. However when I moved to the third bend line I noticed that the cover had developed an unwanted bend and a twist. I carefully worked the unwanted bend out, and carried on with the process.

The end result was acceptable, but not my finest work. I removed the paper template, match drilled the one screw hole, deburred, dimpled, and installed a nut plate.

With the part complete, I installed the air filter and cover, and verified everything fits correctly. Then I took it all apart again, as I’ll need to replace the oil return line.

Tonight I had only a few minutes, so I riveted the right air ramp into position and glued on the template for the left air ramp. I used a pop rivet in the aft-most, inboard hole, because access by squeezer was tight, and I didn’t want to use my rivet gun for fear of bending something.

Tonight I shaped the right hand air ramp.

This required sticking on a paper template, then, following a sequence of bends, shaping the piece until it conforms to relatively smooth curve. It’s a conical shape, so one end is a much tighter radius than the other. I managed to get the shape fairly close, but I ended up cracking the end with the most narrow radius. I stop drilled the crack, then filed out a relief notch to mitigate the risk of further cracks.

I then match drilled the holes into the baffling, and dimpled them. Dimpling the aft most holes was a little annoying because it was too far from the edge to use my squeezer. I used a pop-rivet dimpled instead, which doesn’t give great results, but good enough in this case.

This week I chipped away at the baffle tension rods over a series of evenings. I didn’t actually have a die for cutting the threads, so I had to order one from Aircraft Spruce. These were fairly easy to make, and came out looking good. Some more practice with cutting threads might have helped, but I got the hang of it pretty quickly. When bending the rods I used a block of wood with a slot cut in it to stop the rod rotating, which allowed me to bend both ends of the rods in the same axis.

Installing the rods was fairly easy. I cut a few lengths of 1/4 inch tubing to help prevent chaffing, although there weren’t many areas where interference is possible. Once I had the tubing slid over the rods and positioned correctly, I used some RTV to bond the tubing onto the rod.

With new crush washers in hand I also took time to install the remaining baffle hardware, and torqued everything.

Today I spent time adjusting the front baffles to fit nicely against the engine case. The front left baffle took the most adjusting, and after several iterations I was happy with the fit.

With the baffles fitting nicely I went ahead and installed the hardware and torqued everything up. I have run out of -40 star washers, so I ordered some more and put tape on the screws that were missing washers.