Chapter 23 – Bending aft baffles

Today I started down the road of bending up the aft lower baffles to get them fitted onto the engine and hopefully put the engine baffles in my rearview mirror in short order.

In addition, I’ll note that I wasn’t liking my options thus far on how to secure the exhaust pipes —both to each other in pairs and to the engine to ensure none depart out the aft cowl opening into the prop, if there ever were a crack or a break— so I took another hard look at the instructions that came with the cowlings from Mike Melvill.  It was at this point I decided to mimic closely what he did and press forward in a different direction on my pipe brackets… Melvill style! (more to come on that in the near future).

I started my baffle bending endeavors by deciding what order I needed (or could) bend each baffle without “painting” myself into the proverbial corner of blocking the ability to do a certain bend by having done another preceding one that prevented access to it, or at least making it exponentially more difficult.

The first bend for both left and right aft lower baffles was the big 90° one on the metal brake.  Here we have the aft lower left baffle ready for bending . . .

And post bend.  Honestly it took more time marking the bend line and applying the protective tape then the 30 seconds to bend the darn thing!  I then repeated the process for the right side baffle.

Not shown in this post is the 2 front tabs on the forward side of the left aft side lower baffle that I bent downwards 90°.  These tabs will get RTV’d to the CF cylinder fin baffles to seal this lower baffle to the engine.

As you can see, the 2 outboard tabs: top and front (“shelf and skirt”) have not been bent yet.

I also checked the fit down below with both the exhaust pipes and the alternator.  I could tell by the alignment with the alternator that the outboard top corner of the baffle needs to come down about 1/8″ while the entire baffle needs to be rotated CCW to do that.  That will require some judicious trimming around the inboard baffle edges where it meets the cylinders… trimming notes already annotated.

I then mounted the CF 180° air induction intake tube to do a fit check with the baffles.  Here I’m holding a piece of cardboard up against the back apex of the air induction tube to check clearance with the new lower baffle.

It may be a bit difficult to see the aluminum baffle…

Which is why I grabbed these progressive shots below, to show the relationship between air induction intake tube and the bottom edge of the lower baffles.  I’m not worried at all here with clearance because I’m going to glass in (ok, CF) a mini-bulkhead wall into the lower cowling that will sit just aft of the air induction tube and stop at a height about 1/2″ below the aluminum baffle skirt.  Clearly the sealing material on the bottom side of the aluminum baffles will then seal against the top edge of the bulkhead (aka “aft bottom cowling reinforcement rib”).

Beyond the big 90° bend on the right side aft lower baffle, I did a bit of the opposite as far as the perimeter tabs are concerned:  I did the one upward bend along the front edge, which is the tab where the baffle gets physically mounted to #2 cylinder via a screw.  I also bent the 2 outboard tabs (top: down and front: forward).

Just as on the left side, I’m using a sheet metal bender that is common among HVAC guys for working sheet metal ducts.  If the material is clamped properly, this basic tool is quite handy and works a treat.  No issues so far (knock on wood!).

Here we have the top tab bent down 90° on the outboard side of the right aft lower baffle.

And then the front tab bent forward 90° on the outboard side of the right aft lower baffle (note the upward bent baffle attach tab on the right side of pic).

Although all taped up to prevent any untoward scratching, I grabbed this shot of the right aft lower baffle.

It was getting late and Jess was over making dinner, so I called it a night.  Tomorrow I’ll bend all the remaining baffle tabs and then dial in each side to fit.  If all goes well I might actually do the final install of the alternator with belt tensioned correctly as the left side baffle gets installed.

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