Building the 1/4-Scale 5 HP Red Wing: Part III


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Editor's note: This is the third installment in a planned four-part series on building the scale Red Wing engine.

Hello again! If you caught last month's article, you will remember that we covered milling of the large pieces. This month I want to expose you to some of the smaller and more difficult pieces to work with.

Step 9: Preparing the Crankshaft

The crankshaft is an interesting place to start. I had never made one before, but I was sure it would be a piece of cake. The crankshaft is made of 1/2-inch round material. The throw is 1-inch long and made of 3/8-by-5/8-inch flat stock. The throw shaft is 7/16-inch (0.437") round material.

The instructions call for silver-soldering the pieces together. I chose to braze the pieces and it worked very well. Here is a tip for those that haven't thought of it: The 1/2-inch crankshaft can be left in one long piece. The throw pieces are slid into place and everything is brazed. After cooling, the section of the main shaft that is not supposed to be there can be cut and removed. Leaving the main shaft whole helps to insure the finished crankshaft is straight.

The keyway can be cut one of two ways. You can use a 1/8-inch (0.125") end mill or a woodruff cutter like I did (Photo 1). Either way will give good results as long as the crankshaft is clamped in place securely.

Step 10: Completion of the Fuel Tank and Working on Small Parts

In the first article I talked about turning the bottom of the engine frame into the fuel tank. I milled a 1/8-inch recess at that time. Now is as good a time as any to finish the tank.

A piece of sheet metal is cut to the same size as the recessed area. JB Weld is a good product to use to hold the sheet metal in place as well as seal everything. Gasoline will not cause JB Weld to deteriorate. I liked the idea of an integral tank as opposed to building one that could vibrate and possibly become damaged.

The small parts take some time as well as a little thought to finish. It is difficult to hold them in place while trying to mill. The first thing I did was take all of the small parts and put them on a 1-inch belt sander. This knocked off all of the funny-shaped edges that were left over from the casting process.

After belt sanding, I started working with the governor arm bracket. I located the center and drilled a 1/2-inch hole. This was so I could mount the part on a shaft. Using the lathe, I turned the base of the bracket until it was round and of the proper dimension.

For the next step, I moved to the mill and milled the part to the proper thickness. Next I cut the 0.132" slot in the ears, drilled all the holes and countersunk the holes used to mount the bracket to the flywheel (Photo 2).

The distance between the ears has to be enough to allow the shift collar to move freely on the crankshaft. That dimension is not on the blueprints; however, the dimension for the shift collar does answer this question.

The governor weights are funny-looking little things. They remind me of those plastic drinking birds on a stick. They can be a pain to make because they have to be fitted to the flywheel, governor bracket and shift collar. A lot of the shaping was done on the 1-inch belt sander. I am beginning to like that little machine!

I did some of the painting earlier simply because I was impatient. Since the flywheels were painted, as well as the engine frame and base, I started to put some of these things together.

Step 11: Completion of the Flywheel, Governor and Crankshaft Assemblies

The right side flywheel and crankshaft can be seen in their assembled position in the opening photo on page 15. Photo 3 gives you a frontal view of the engine looking right down the cylinder to the crankshaft at the other end.

Photo 4 gives a view of both sides of the left flywheel with the governor bracket and governor weights assembled. The weights connect to the bracket with two pins. I made them out of 1/8-inch brass welding rod.

The weights are connected to each other with two springs and studs. I also made the studs out of the brass welding rod. I threaded the rod for a 5-40 nut. I didn't have any 5-40 nuts, so I took a 4-40, drilled it out and re-tapped it.

If we add the shift collar and crankshaft gear, it will complete the entire crankshaft and flywheel assembly (Photo 5). I realize the flywheel will have to be pulled numerous times before I am finished, but it does make it look like I have actually accomplished something!

All of this has been fun so far. Remember, I am not a professional machinist. I have had very little experience and am learning as I go. Want me to prove it to you? My nightmare is about to begin!

Step 12: Cylinder Head Torment

The cylinder head is a beast from hell! Every single piece of this casting has to be turned, milled, drilled, tapped, countersunk and rotated a specific number of degrees before the next set of holes can be drilled. I messed up the first one before I even got a good start. I messed up the second one, but was able to save it. I may do a third one just to see if I can make one with no mistakes, but I am not going to hold my breath. Let me tell you what makes this such a tough little part to make.

The raw casting has a connecting rod bracket on the left side, the exhaust port on the right side and the mixer port located on the under side of the head (Photo 6). The arrow shows the portion of the head that fits inside the cylinder.

This portion has to be turned to the diameter of the cylinder. The area surrounding the part with the arrow has to be faced. The part with the arrow needs to project into the cylinder 0.375". The thickness of the head, not counting the projection into the cylinder, is 1.025". This thickness can be faced in the lathe or on the milling machine. This may seem like a lot of work, but we are just getting started!

The mounting holes for the head are 18.73 degrees clockwise from the vertical position as viewed from the front. I marked the location for the holes and used super glue to attach the head to the cylinder. This let me drill the head and cylinder at the same time. I didn't want to end up with a head that wouldn't bolt up with the cylinder. Looking back at photo 3 you will see what I mean about the bolt hole positions.

The holes for the valves are drilled 30 degrees clockwise from vertical. Photo 7 gives you a good view of the valve ports as well as the holes for the valve stems. This is where I messed up the second head. I went 30 degrees the wrong direction. If you look carefully at the photo, you will see my repair job for one of the holes I drilled in the wrong location. Does it really matter? Unfortunately, it does.

The reason is that the valve chambers you see in photo 8 are positioned so the holes drilled to mount the mixer and exhaust actually intersect with the appropriate chamber. The arrow on the left shows airflow from the mixer to the intake valve chamber. The arrow on the right shows airflow from the exhaust valve chamber to the muffler. I told you this was a beast!

The holes drilled for the mixer and exhaust are tapped using 1/8-inch NPT pipe thread. The 1/8-inch NPT is used a lot on this engine. Be sure you have one. Well, this is enough fun for today.

Next month we will cover the piston, connecting rod, push rod, timing assembly and valves. This will complete the engine with the exception of the mixer. If we are lucky I will have time to cover the mixer and fire the thing up! Only time will tell.

Contact engine enthusiast Richard Allen Dickey at: 246 Skyview Lane, Yellville, AR 72687;

Contact the Red Wing Motor Co. at: (660) 428-2288;