The new engine

Having completed most of the preliminary work for make ready, I wanted to tackle the combustor itself. The idea is to make a combustor that looks like it is one solid piece when done. This means a lot of welding and even more grinding. The neighbors would really love me after that. The good news is that most of the neighbors were out for the Easter holiday, so I had the ability to make as much noise as I wanted. Yeah, the radio was blaring, grinders were whirring, and I was beating metal into submission. It was a great weekend!

Cutting the tube down to size

The first thing I had to do was cut the combustor tubing down to size. It is an interesting note that I was not expecting to see this pipe until some time next week. I guess the Easter Bunny brought me a present in his little basket. Funny, the Easter Bunny looked just like a UPS driver this year!

The finished cut

To get the cut, I first made sure one end was perfectly flat. There is a really easy way to do this. Take a large piece of posterboard and wrap it around the tubing. Line up the ends of the posterboard with it puled tight, and the edge of the posterboard will be a perfect line around the tube at a 90 degree angle to the axial plane. This means that you can mark the perfect cut easily. After I marked the tube as close to the end as I could, I used the angle grinder with a flap disc to clean the edge. I then measured up 9.5 inches and made a mark on opposite sides of the tube. Using the posterboards method again, I lined up the edge with the marks and made a new line. I then followed around with the cut off wheel. A little clean up with the flap disc and she was almost ready.

I chose the 9.5 inch length based on the 1/4 inch end rings that would be welded on. The addition of 1/4 inch on each side will give me a 10 inch long combustor and flame tube.

Beveling the edge

The combustor tubing has a 1/8th inch wall thickness. I used the angle grinder with a 24 grit flap disc to put a beveled edge all the way around both edges of the tube. By doing this I can get a better weld penetration on the combustor, which I will need since the welds will be ground smooth.

Threading the spark plug holes

Next up I wanted to thread the spark plug holes which will be used to hold the ignition spark plugs for the combustor. Now, I do make some pretty good mistakes sometimes. This was one of them. Before sending the parts out for laser cutting, I noticed what I thought was an error in my CAD drawing. It looked like the holes I spec'd for the spark plugs were too large. Since I was in a hurry to get the parts files sent to the cutter, I just adjusted the holes to a quarter inch and figured that I would drill them up when the pieces arrived. At the time, it was completely oblivious to me that (A) the holes were the right size in the drawing, and (B) I don't have the right size drill bit for the reamer tap I would be using to thread the spark plug holes.

A little ingenuity on my part with a high speed reamer cutter and the drill press soon enlarged the holes a bit larger than 1/2 inch so they could be threaded. The reamer can be seen in the picture above threaded into the plate. To make this job easier I actually bolted the end cap to the drill press table.

Injector tube

Pictured above is one of the little injector tubes that get the fuel into the combustion chamber. They are a really simple part, being only a half inch outside diameter tube with a 3/8 inch inside diameter. I hold them in the vise on the drill press and chuck up the tap to hold it absolutely vertical. I then hit the switch on the drill press and pulse it on for just a second before turning it off and bring the tap down into the tube. I can then release the chuck and finish tapping the tube by hand, knowing that the tap is perfectly aligned in the injector tube.

Five injector tubes in the end cap

The injector tubes are 1 and 1/4 inches long so that 1/2 inch will protrude from each side of the plate when they are welded in. The nozzles can then thread into the inside and the fuel supply will attach to the outside. The threads are 1/8th inch NPT tapered pipe threads. The 4 outer injectors will be used for the main fuel injectors, while the central injector will be used for a smaller nozzle suited to starting the engine.

End ring ready for welding

It was finally time to weld on the first end ring to the combustor housing. The first thing I did was to mark a line running parallel to the axis of the tube down one side of the tube outside wall. This is so that I can align both end caps to this mark and have the bolt patterns identical on opposite ends.

Magnetic alignment blocks

The more I use these magnetic clamps, the more uses I find for them. They are just what the doctor ordered for aligning parts such as the end ring to the combustor housing. The magnets do not hold the plate in place so much as they just hold it centered.

Tacking the end ring

With the end ring lined up and double checked, I tack welded it to the combustor casing. Since this kind of welding can cause the ring or combustor housing to warp very easily, it is imperative that you check the alignment often and go in small steps. I used stitch welds alternating from one side to the other to keep heat buildup to a minimum.

The welded combustor housing

After welding the first ring in place, I was happy with the look. I checked and found good weld penetration in the part, which is critical in something like a combustor.

Injector cap in place

I bolted on the injector cap to check for any warping. There was none, and the cap sat nice and flat. This is also a reason for the materials I chose for the new combustor. The 1/4 inch thick rings are much more resilient to heat warping, as is the 1/8th inch wall tubing.

The exhaust manifold bolted on

After seeing the injector end cap, I just had to see the exhaust manifold cap in place. I am pleasantly surprised how easy it has been so far to make all of the pieces line up correctly. This thing is really starting to look good!

View down the pipe

This is always one of my favorite views. It is also the last thing the hot gasses will see on their journey out of the combustor. So far, so good. I am sure that you can tell from the pictures above that it was pretty dark out again. I figured it was time to shut down for the night. The next morning I would get up and finish welding the other ring and I would then grind everything down nice and smooth.

Welding the injector tubes

The next day came quickly and I got straight to work after waking from my restful sleep the night before. Funny how good you can sleep when you are just exhausted. The first order of business was to weld the injector tubes in place from the inside of the injector end cap. The tubes were aligned leaving 1/2 inch protruding from each side and then tacked. After inspection to insure that everything was lined up, I ran a nice fat weld bead around each one. Notice my little tool in the right of the photo. It is just a piece of 1/8th inch thick plate with the ends ground perfectly flat. It is really good at removing the little spatter blobs that are prevalent with flux core welding.

Rings welded and ground

I wasted no time in getting the other end ring welded to the combustor. By using the line down the side of the tube, I aligned it to the one already welded to the other end. Grinding consisted of multiple passes with a grinding wheel, then a 24 grit flap disc, followed by a pass with a 60 grit flap disc. The finish came out very nice. I found a couple areas of incomplete penetration where I had overlapped welds when starting and stopping. I ran new beads and ground them again and everything was OK.

Combustor attached to turbo

I couldn't wait to get the combustor attached to the turbo, so on it went. The exhaust flange bolts on first, then the combustor housing bolts to the exhaust flange.

Cap head screws

The cap head screws really add a nice look to the engine when everything gets mounted together. I have to admit, they are much more expensive than regular grade 8 bolts. Who cares! It just gives it that "jet engine feel" I think. You may notice here that it would be impossible to put the bolts in position behind the exhaust bend. I already thought of this, and there are 3/8 inch studs that thread in and then a regular hex nut can be fit in behind the bend and tightened with a wrench.

The combustor just fits in the stand

I really thought that I would have to make a modification to the test stand to be able to fit the new combustor in there due to the new sideways orientation. If you look closely at the upper left you can see that it just barely clears the side rail of the stand. Also of note is the stand offs used to keep the heat shield away from the end cap. One more thing that needs pointing out is the beautiful woman in the background, below right in the picture. My wife came out for a visit and she just sits and watches me while I work. A wonderful woman for sure, and I never have to worry about there being good music on the radio when she is in the shop! Metal - check, welding - check, new engine - check, wonderful wife - check, yeah it was a good day in the shop!

Injector side

The new combustor sure does look a lot different from the old tiny one. It does not stick out very far past the side of the turbo housings, and there is now plenty of room up front beneath the turbo compressor for a nice oil tank. It is funny how a combustor that is so much bigger will allow me far more space to work with in such a small motorcycle.

Angle view

Here you can see more clearly that the combustor will not really stick out the side of the bike very far at all. I may have it angled up slightly on the bike to give more ground clearance during right turns though. I will have to see how that works out once I get the plumbing from the compressor to the combustor. The new 3.5 inch pipe bends have not arrived yet, but I expect them any day.

Now that's an engine!

Overall, I am very pleased with the new engine. It looks much better than the old one, will perform with better thrust, and gives me more room to work with. The benefits keep showing themselves as I work with it more and more. As long as the exhaust bend works OK, this engine will be a winner.

Picture Montage

As of Friday morning 4-14-06, I spoke with a potential new sponsor. They would bring a lot to the table and we hope to get them on board soon. I took some pictures of the project to send to them, not realizing that the parts I desperately needed would all be arriving shortly. After looking at the pictures, it is almost a retrospective of what we have done so far. I thought I would share them with you here and let you recap some of the journey we have shared together. Also take note of the difference in size between the old combustor end cap and the new one, both visible in the last photo. I hope you can see the strides we have made this year to bring you some of the best projects on the internet.

New parts will once again be here soon, with another update to follow shortly thereafter. This time I have a tracking number and know they will arrive! Ahh the power of technology and little things like tracking numbers. Thanks again for reading, and please remember to support the site. The more support we get, the better the projects will be.

Russ W. Moore
Bad Brothers Racing

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