Another builder’s baffles

IO-390 Baffles for the RV-7/7A

Contributed By Bill Gill

Van’s baffle kit for the IO-360 200 hp fits nicely on the 390 with a few modifications, except for the front baffle. Here, the forward mounted governor pad creates some challenges. Since the contour of the case in this area closely matches that of the IO-540 used in the RV-10, I began by ordering the front baffle pieces and brackets for the IO-540 RV-10. You will use the RV-10 front baffle parts to develop a cardboard pattern that will be used to fabricate the front baffle parts. The following photos illustrate this process.

The front-right baffle installed here is for the IO-540 RV-10. It fits the case nicely and the lower edge closely matches the lower inlet floor angle, but it does not extend forward far enough (should extend slightly beyond the ring gear) and was a little short as well. The left front baffle shown was fabricated using the RV-10 baffle as a pattern, but is more complicated due to the governor and differing lower inlet floor angle. One must consider where the prop governor cable will penetrate the lower inlet floor to prevent interference with the FAB air box.

The left front baffle fabrication began with developing a cardboard pattern and tracing it onto a piece of .032” 2024-T3. Getting the bottom edge to match the lower inlet floor ramp is difficult and may require several iterations to achieve the desired outcome. Hint: have plenty of .032” material.

Front left baffle…marking fold lines, trimming, deburring, etc.

Front left baffle: At this stage, the baffle can be installed on the lower inlet ramps. The #8 screws are installed from the bottom of the inlet ramp into the three nutplates and the top “tab” is match-drilled to the mounting bracket.

Notice the dimpled screw holes in the lower inlet ramp adjacent to the front baffle. These are used to secure the FAB air box. However, the bracket for the FAB air box would interfere with the prop governor cable. As a result, another front baffle was fabricated which shortened the distance from the engine case to the outside edge of the baffle. This resulted in the baffle being “angled” as it extended rearward (see the following photo).

Notice the clearance between the baffle and the screws. Also, this required a ½” spacer on the governor arm to position the governor cable close to the engine. The upper inlet ramp that gets installed on the upper cowling was initially trimmed so that it fit completely around the upper half of the governor, but aft portion of the ramp in the governor area was later trimmed away to allow the baffle seal to fit better. Looking at the baffle seal around the governor in the photo above illustrates this.

Here, you can see the space between the governor arm (where the cable rod end attaches) and the baffle.

Even though the IO-540 RV-10 front-right baffle fit closely on the 390, it still took many iterations to get one fabricated that fit correctly.

The front right baffle is secured using two angles – one alongside the edge going toward the ring gear…

…and another angle on the inside near the cylinder flange

Completed photos (except the rubber baffle material is not yet installed on the lower cowling inlet in these photos)

A hole was cut on the baffle just large enough to pull it over the end of the governor with the arm(s) removed.