Folded Edge On Exhaust Manifolds

The next step is to form an edge along the outside of the seam between the 2 shells.  The edge of the upper shell on the original manifold was folded 180 degrees so it covered the edge of the lower shell, leaving a smooth finished edge.  The welding holds the shells together so this just creates a smooth finished edge.

I've had a lot of ideas for how to do this.  Slowly the complicated ideas have all been abandoned.  The easy way is probably how the factory did it, just a hammer and a dolly.

There are a variety of straight sections, inside curves and outside curves.  While the details are slightly different for each, the method is basically the same, fold the upper edge over the lower edge and hammer it tight on the dolly.

On thing I quickly realized was that some of the ends of the shell needed to be trimmed. You don't want the folded end to stick out past the welded seam after folding.  The edge on the left of the tube will fold without sticking out past the end, while that on the right needs to be trimmed first.

The ends were trimmed with the snips where the angle formed at the end of the lower shell was less than 90 degrees.

The spot welds are quite strong and the steel at he edge is still soft since it has not been worked like the tube areas.

The first step is to hammer the edge down at about a 45 degree angle.  This gets hammered around the lower shell, in steps of about 30 - 45 degrees, until it is past 90 degrees.

I'm using a Handy-T Dolly from Fournier ( a present from the grandkids).  It fits the 3/8" radius in the corner of the shells so it won't nick them.

With the shell resting on the dolly the fold is completed and then hammered tight.

For the inside curves I used a round hammer.  This hammer has a flatter curve than my ball peen hammers.

Again you just work back and forth over the length of the seam slowly bending it over.  The steel is soft enough that it stretches without cracking,

Once it's past 90 degrees I move to the dolly to finish the fold in 30 -45 degree increments until it is flat, then tighten it.

This was the longest inside curve and it formed just fine.

The outside curve is done with the flat side of the hammer working the length of the curve in 30 -45 degree increments.

The edge looks wavier as you work because the outside edge is longer and the steel needs to be shrunk to make the fold.

As you approach 90 degrees the edge is shrinking and getting less wavy.

Again, once the edge is past 90 degrees it can go on the dolly to slowly work down tight.




You can see how trimming the end of the upper shell left a nice end to the fold.

For the long straight edge I used the seam pliers to slowly work the bend to about 90 degrees and then hammered it, along with the long outside curve on the forward tube.

It took less than 30 minutes to fold all the edges on my first shell.

Simple still seems the best way to make things.