First Good Exhaust Manifold Shell Half

 I keep thinking I can do this with a few tools.  Some how it never seems to work that way.  In fact I have ideas for more tools to make this all work better.  I need to get a used wooden baseball bat.

 Part of the trick to this is which bolts to have tight and which loose.  Tight bolts hold the metal from moving and allows the metal to be stretched.  Loose bolts let the metal slide so you don't have to stretch it too much and fracture the steel.

The first tool is the rivet gun and narrow tool.  the smaller tip area gives higher psi. I start at the intersection of the tubes and work up the edge of each tube, but not along the long straight bottom.  I then go across the bottom of the tubes and work toward the top to get the forming started.

 The bottom gets formed with a piece of 2" dowel, until I get a dead baseball bat.  It forms the bottom as a nice straight curve and pulls the steel out of the form block rather than stretch it, which would be too much work and it would end up wrinkled.

There is a wrinkle starting at the top because I went to far with the bottom dowel.

 The top gets formed with a short piece of dowel.  If I had worked between the 2 dowels with smaller deformations I think this would have come out smoother in the radius going to the outlet.

We'll see how I do on the next one.  At this point it's time to go back to the inlet tubes.

 As I form the inlet tubes the inlet itself closes in because the metal slides in the block.  Every so often I stop and use the dolly to stretch the excess so the bend doesn't get out of control.

 Once the tube is to the correct depth near the inlet, the actual inlet needs to be formed.  That's where the modified bolt comes in.  I can drive it down to square up the inlet and get it to the right depth.

 There is still more work to be done forming the tube and I don't want the inlet to close back up, so I made some blocks of oak to drive down in the inlet. By clamping it in place while I work on the rest of the tube, the metal can't slide in.  I also tighten the 3 bolts right at the inlet.

It turned out the anvil on the 6" c-clamp was to big and the clamp kept sliding off the edge of the plywood.  The adjustable clamp worked better.  Even though you can't get it as tight.

 All the forming is done except the outlet.  I couldn't get it to form a nice radius so I decided to make a tool to pound into the block to form it in one hit.  I wanted Oak but I settled for some treated Yellow Pine from a piece of 4x4.  I sawed it to 2 3/4" wide but put a 1 1/8" radius on each corner.  The idea was to over bend the radius a little so it would spring back to 1 3/8" radius.  It worked great.  Problem solved.

 It came out great.  There is a little roughness in the tubes, but I like it.

 The inlets came out the right size without any cracks or tears.

 The one mistake I made was to work the tubes from front to back.  I should have done the front tube then the back tube, followed by the middle tubes.  It all slid slightly toward the front.  You can see from the blue lines, which started at the edge of the form block, where the steel slid and stretched.

 Here is the comparison of the formed shell with the blank.

You can see from the top view how well it worked to let the steel slide into the bend along the straight bottom edge.  The cuts into the corners where the tubes join worked very well to let the steel slide into the tubes.

With a good Left Hand Bottom shell I'm ready to make the opposite shell.  I worried that my plan to swap the top and bottom pieces of plywood would never work because there are 32 bolts to align which meant the holes in the block had to be almost perfectly perpendicular to the block.  As it turns out the Shop Smith is up to the task.  I drilled the bolt holes 1/64" oversize so the bolts would go in easily but still be snug.

They all fit perfectly.  I didn't have to re-drill a single hole.

Time to make another shell.

Some Better Tools For Forming The Exhaust Manifold Shell

 From the first piece I learned I needed a piece of wood under the flat section of the collector so It would end up flat not bulged in the center.  To do that I needed a piece of wood which tapered 1/4" form the end of the first inlet tube to the outlet end.  I decided to use the scrap cut from one of the layers since it would fit and stay in place without anything to hold it in position.  I need to be able to flip it over to do the other side of the shell.  To taper it I drew a guide line on each edge and the used a 24 grit disc on the sander.  I smoothed it a little with the belt sander.

 I started the forming with the along the edges with the narrow tool and then used it to start the shaping of the inlet tubes.

 I used some 2" dowel to make some tools to form the collector area so it would have less dents when all done.  I left the lower bolts loose while forming the collector so the steel would slide rather than just stretching.

 I decided to make a better forming tool using the 2 5/16" ball.  Unfortunately it has a 1" threaded end.  The other balls are 3/4" as is the hitch insert I used as a handle.  I decided it was easier to make a handle then to modify the hitch end.

 I used some scrap 3/16" x 3" steel from making the WACO NINE nose rib forming tool.  I sawed out a handle about a foot long with a 1 1/4" wide handle to fit some dowel I have.  I made the ball end big enough to fit the base of the ball and cut a 1" hole with a hole saw.

For the handle I drilled 4 holes in the steel for screws to pass through.  I split the dowel and ran 2 screws from each side though the steel into the other half of the dowel.  I rounded the ends of the dowel for a nicer job.

I stacked enough 1" washers, from Tractor Supply, to get the nut flush with the threaded end of the ball.

 The ball shape I wanted was more oval than the first ball.  I ground flats on the 2 sides working to keep them equal distance form the center by eye and by making the flats the same diameter.  I ground until the ball was 1.74" wide.  I used the 24 grit disk on the disc sander.  I was able to see what I was doing better and the 24 grit cut much faster.  I still had to cool the ball from time to time.
Next I radiused the top on the 2 sides with the sander.

 I then worked the top of the ball to a nice even curve from front to back.
With these curves established I blended in the corners.  To finish it smooth I used the belt sander.  There is an area at the top between the roller and the backing plate where the belt is unsupported.  It works great for blending  with less sharp edges on each pass.  Next I lightly filed off high edges and then worked it in the palm of my hand with a piece of 120 grit belt to smooth it better.  I finished it with Scotchbrite.

It's way better than the first one.

 I turned the ball at an angle to make it comfortable to hold with the axis of the ball in line with the inlet ends of the pipes.

As you work down the pipe, holding the ball at about the same angle makes the ball naturally wider to fill the shape of the tube.

It really works great.  This is what the first tube looks like after the first rough shaping pass.  Very cool!

First Exhaust Manifold Shell Formed

 To control the depth of the forming I made some gauges from a heavy card stock.  It was easier to cut them from the card stock than steel.  They worked well so I'll probably make more permanent ones from my usual galvanized steel.
I made them so when the depth is correct they set flat on the plywood.

 There is about 1/2" to go to get it deep enough here.  To form the steel this deep I bought a 6 lb. sledge hammer.  The hammer I was using is only 3 lb.  I looked at even bigger hammers but I couldn't control them with one hand.  I also cut off the handle to the same length as the 3 lb. hammer and smoothed the face on the belt sander.  It had deep machining rings on the face.  The 3 lb. hammer works great for light smoothing hits.

With a little work the pipe is now deep enough.

 I did all the forming with the 1 7/8" ball.  I have an idea how to do this with the 2 5/16 ball  I just need to rework it along the lines of what I did with the 1 7/8" ball.  I also need to improve the shape slightly.

It still needs some planishing to smooth it and I tore the steel in the corners of the inlets.  I think I know how to solve these problems on the next one.  This one will go into the recycling bin.

 You have to look close to see it but I set the blank template under the formed part to see where I need to alter the template.  I'll experiment with some small changes on the next one like adding a little steel in the inside curve at the outlet end.  The forward inlet inlet pulled the steel in a way that jammed on the form, so I'll trim it at an angle to allow for this.