Things have been slow in the garage for a while as we tried to source materials to correct the problems with the first combustion chamber. The new outer casing of the chamber and the flame tube will have to be larger, as will the plumbing supplying the air from the turbo's compressor to the combustor.

The new design being worked on is 8 inches in diameter, and will have to be mounted in a totally different fashion in order to fit into the frame. The flame tube will be much larger, going from 2.5 inches up to 5 inches in diameter. The length will remain 12 inches however.

There have been other problems to work out, however, and they will be addressed in this update.

The shock absorber in the way of the exhaust

As is clearly visible in the picture above, the original shock absorber mounting location was in the way of the jet exhaust. Because of this, it had to be completely cut off and relocated further back in the frame. Not a problem, just pull out the cutoff wheel and rip it out! Then grab the welder.

The exhaust path and new mount location

The shaded green area in the picture above shows the planned path of the exhaust from the engine. The red line shows the location of the original shock mount location, and if you look carefully you will see the new shock mount to the left. The location is further back in the frame, and will allow the exhaust to make its way to the rear of the bike.

The solid shock bar

The new shock location changed the geometry of the shock to the point that compression of the shock spring happened with much less weight on the bike. The lower shock mount on the swingarm will have to be moved further back as well to avoid this problem. For now, I fabricated a solid bar to fit in place of the shock so that the correct ride height can be kept during the rest of the fabrication process. You can see the bar pointed out by the blue arrow, and if you look closely at the frame you will see how far back it has been moved. Look for the spot where the original mount was ground off inside the frame, almost directly to the right of the new location.

The relocated shock position

With the new shock position, there is much more room to route the exhaust from the engine without getting too close to the shock. I have sat on the bike with the rigid shock bar in place and had someone push me. The ride is not all that uncomfortable, and in the end I may machine a better bar and leave it this way if it is not unbearable. If I do decide to adjust the lower shock mount, then it will just be moved back on the swingarm by about 1 inch and should prove to be effective. I did a brief test with a very rigged setup and it worked. Sorry I don't have a picture, but the setup was very embarrassing and I didn't feel like showing the depths to which I will lower myself to sometimes. Yeah, it was that bad of a test setup!

Clearance for the exhaust

The exhaust now has a pretty little space to make its way to the rear of the bike, and ultimately, the afterburner. The shock mount is right above the rear tire, and the exhaust will travel above it, and below the arched frame support, which is also the seat mounting location. Yes, the hot gasses will be very close to yours truly when this gets done.

Original shock location

The red arrow above points to a piece of steel I am holding in the original location of the shock mount. The blue arrow is the new mounting location, about 6 inches to the rear of the bike.

Original shock location

Again, the red and blue arrows show the old and new shock locations respectively. As you can see, the shock now mounts to the smaller frame rails that hold up the rear subframe of the bike. There does not appear to be a problem with this setup, but if the need arises, I will strengthen the frame with gussets in this location.

Straight through from the rear

This image shows the view of the redesigned mounting locations, and the clearance that has been gained. Air flow will be free to travel from the front of the bike, all the way through to the rear. If you look carefully, you will notice the new oil cooler located all the way in the front.

The oil cooler

The new oil cooler mounts in the frame right behind the steering stem. The location was almost ready made for the cooler to fit right in. The only problems encountered were that the mounting tabs on the cooler were a bit large for the area. The original tabs ran the length of the cooler, and would foul on the frame. A quick trip to the shop bench with the Dremel, and the tabs were cut back to a reasonable size. The blue arrow shows the new smaller tabs, and how they fit just outside the frame rails.

B&M plate type cooler

The cooler is a plate type cooler, which I much prefer over the tube and fin type. Tube and fin, is pretty much as the name implies. There is a tube that zig zags back and forth, which is surrounded by thin metal fins similar to a radiator, or outdoor air conditioning unit. The fins are very prone to bending and can block the airflow if allowed to do so. The plate type uses pressed metal plates which are brazed together to form rigid little tanks for the fluid to flow through. As they are rigid, they are less likely to be damaged by debris from the road. This is very important when you want the maximum cooling available for your oil stream, as is the case in a jet engine application.

Cooler mounting tabs

Tabs were fabricated to match the contour of the frame, and welded in place to match the mounting holes of the oil cooler. The location will allow for air to move straight through the front fairings and into the cooler while the bike is in motion.

Front cooler view

The oil cooler was small compared to what I would have liked to use for this size engine, but once again space dictates what I can and cannot use in the build. The cooler takes up every bit of available room in its mounting location, but looks as if it were made to go there originally. The width matches the bike frame perfectly.

Flow of air will go under the tank

When the air enters the front of the oil cooler, it will exit through the rear, and under the fuel tank. Fans underneath the tank, and behind the cooler will help to keep the maximum amount of air circulating through the cooler. The air will then travel further back under the tank, and also server to keep components under the tank bathed in a thermally insulating cushion of air. Without the fans, the oil would reach a high temperature very quickly while the bike is not in motion, so they will also serve to aid cooling while at rest, and during the cool down process after the engine has been shut off.

Air path under the tank

The view above is from underneath the tank. The front of the bike is to the right, and the blue arrows show the path the air is expected to take when completed. A set of fans will be placed directly behind the oil cooler, which would be to the left in the above view. The fans will be pancake type fans, or muffin fans, such as are used in computer cases. If necessary, a plenum will be created to make sure the air is diverted to exactly the right areas.

The new combustor is getting some attention after a long wait. The problem was in sourcing the correct steel tubing to use in the fabrication. Thanks to Gary and Matt, the materials are arriving and the new combustor will start to take shape.

I will take a moment here to shamelessly self plug my T-shirts. The T-shirts are pretty cool, if I must say so myself. If enough people would start wearing the T-shirts, then the meager proceeds could help to fund the completion of projects here on the site, as well as help get new projects started. If you have the means, they are nice and would look good on you! If you would like to help the site in other ways, through sponsorship, donation, whatever, please feel free to contact us through the information on the contact pages. Thanks to all of you who help support the site so that we may continue to bring these crazy projects to you!

Russ W. Moore
Bad Brothers Racing

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