Welcome back to the garage! Pull up a chair and grab a nice cold soda out of the fridge. This time around I am going to show you how the combustor will be connected to the turbo. This is pure, good old fashioned hand fabrication with a little redneck engineering thrown in for good measure.

In previous updates, the new combustion chamber design was shown. Those parts are being water jet cut for assembly, so until they arrive there is some small work to be done. The combustion chamber exit has to be directed into the turbine inlet. In the previous engine design, the process was to cut and re-weld pipe sections. This time, a proper elbow will be fabricated using plate steel.

SolidWorks rendering of exhaust bend

Once again, I pulled out SolidWorks to model parts. The exhaust bend will take the hot gasses from the combustion chamber and direct them up into the turbine housing. Using SolidWorks allows me to create the parts and verify their fit before committing to cutting steel.

Paper pattern tracings

The drawings from SolidWorks were used to create paper patterns of the parts I needed to cut. These patterns were then laid out on the raw steel and traced.

Parts layout

Using the tracings, the parts were rough cut from the steel sheet. Once the basic rough shapes were cut, they could be sized to the proper dimensions.

Finish ground parts

To get the parts to the correct shape quickly, the paper pattern was placed over the rough cut steel blanks and clamped in the work bench. The grinder can then be used with a flap disc to quickly bring the steel to the exact size of the template.

Part comparison to tracing

I chose to fabricate these parts this way, because it is much easier than trying to set up a machine tool such as a mill. There are 4 pairs of parts in this assembly, so it is just a quick way to do things. It took me about 30 minutes to make the parts this way.

Bending the radius

To bend the radius in the flat stock, I used the clamping jaws of the work bench and a piece of pipe the diameter of the bend I wanted. The flat plate is clamped into the vise with the pipe and bent slowly and carefully to get the proper radius. In this case, the pipe is 2 inches.

Bent radius

Here the flat plate has been bent over the pipe and is ready to use. I left the plate longer than I would need it to make the bending process easier. The larger radius was bent around a fire extinguisher in the shop that had the right diameter of 6 inches. The bend was performed the same way.

Tack welding the radius

The first part of the exhaust bend that I wanted to make is the radius. I carefully lined up the pieces using magnetic welding clamps and tack welded it together.

Tack welds

Because the material is thin, tack welding is the best way to do this. Heat generated from the welding process will cause the metal to warp and distort. By using small tack welds and ensuring the entire piece is straight, the finish welding will be much easier and less likely to distort the piece.

Welded radius

After proper tack welding and alignment, the part was finish welded. The extra length of metal from bending the radius curves was then scribed and cut with a cutoff wheel in an angle grinder.

Ground weld beads

The welds have been ground in this picture. I have determined that my digital camera just does not like shiny things as it causes the focus to go out a little when taking the pictures with the flash. Hopefully you can get enough of an idea of the rounded edges and nicer look here though.

Welding the stack

The next part was the stack that travels up to the turbine inlet. Since the frame of the bike would interfere with the fit of the combustor if it was centered beneath the opening of the turbine, the stack had to adjust for this. There is a 1 inch offset for this purpose. As was done with the radius, the pieces here are tack welded, and about to be finish welded.

Completed welding

The edges and beads were ground after welding was completed. The finished part will be welded to the combustor as shown in the first photo. The end of the stack that meets the turbine housing will be welded to a plate so that it can bolt on to the turbine inlet..

Ready to fit to the combustor

Final fit to the combustor housing will occur once the main combustor body is assembled. This will assure a good fit of all the components, and make lining things up in the bike frame easier.

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Russ W. Moore
Bad Brothers Racing

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