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28-05 to 07 Joining Firewall & Muffler Assembly


More Proseal is used to seal the seams as the Firewall and Muffler assembly are joined.

After test fitting and masking we decided it was probably easiest to flip the firewall upside down on the bench and drop the lower skins/muffler in from above.

The manual suggests that pages 05-06 are done in one session, so that the Proseal edges are riveted in one go I presume. But I decided to include page 07 as well, since the lower flange on the Firewall is not riveted until that page and that seam also is Prosealed?

Several stages on those pages are not high priority anyway, such as the dry riveting.


The Muffler/Firewall side flanges are pop riveted. I couldn’t fit my fancy pneumatic pop-rivet gun in the space, but they are easily set with a hand gun.

The top uses AN426AD3-3’s, easily reached with the gun.

Much easier to do all this with my rivet partner Tim!


We riveted the Firewall lower flange at this stage, together with the Cowl Attach Plates, Shims and Tunnel Angle.

These were easily set with the pneumatic squeezer.

The manual suggests AN426AD3-4.5’s for the Attach Plates, which with my dimpling/priming were probably just too short.

Having seen the -4.5’s, I used -5’s on the other side and they were a better option.


Here are the Proseal fillets after the masking was removed.

Cover Bases


We back-riveted the Cover Bases using the C-Frame, which gives very consistent results.

Tunnel Sides


Same for the Tunnel Sides.

I was very wary of dropping anything on those lower skins!


This is a view of the mushroom set in the C-Frame, with the workpiece on blocks etc to ensure the set sits flat on the skins.

Once set up it’s very quick to slide the C-Frame from rivet to rivet.

Muffler Shroud Ramp


I used a long rivet set for riveting the Tunnel Sides to the Muffler Shroud Ramp, just for convenience standing at the edge of the workbench.

Firewall Penetration Fittings


I used the last bit of mixed Proseal to seal the Firewall Penetration Fittings.


Quick little job to attach with the screws/nuts.


You’ll need a 11/32″ socket or spanner for the AN365-832A nuts.

Next job is to attach the F-01403 Forward Center Section Bulkhead Assembly!


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