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


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

It's that time again! This month we'll cover the piston, connecting rod and bearing, as well as the timing assembly, pushrod and valves. There is quite a lot of material to cover, so let's get started!

Step 13: Assembling the Connecting Rod, Piston and Bearing

The piston is made of 1-1/4-inch cast iron round stock, 1-3/4-inches in length and uses a 0.312" (5/16-inch) diameter wrist pin (Photo 1). After adding its two piston rings, my wife said, "It's just the cutest little thing!"

I used a parting tool to cut the slots for the piston rings, which worked very well. To hollow out the piston, I drilled a 1/2-inch hole in the bottom while it was still in the lathe. Reaching through the hole, I used a carbide cutter and turned the piston from the inside out until my wall thickness was about 0.100".

To allow room for the connecting rod, I used a 1/2-inch end mill to cut a little deeper into the piston (Photo 2). The arrows point to holes drilled for set screws that are used to hold the wrist pin in place.

The connecting rod was easy to make. However, I did make two changes to the original design. First, I didn't taper the rod. Why? I don't know how! It's one of those things that I have a hard time trying to visualize. It also doesn't matter. The second change was in the way the connecting rod is assembled.

The end of the connecting rod has a piece of 1/2-inch O.D. round tubing turned sideways (Photo 3). This is where the piston is connected to the rod with the wrist pin. The prints call for an "alignment spud" to position the parts for soldering. I thought if I took a 1/2-inch end mill and fed it into the end of the long rod, it would make the perfect saddle for the 1/2-inch rod to rest. It worked beautifully! A little brazing and this part is done.

The rod bearing is made from a brass casting. It was a simple process of squaring the casting, cutting it in half, milling it to size and drilling some holes.

Step 14: Getting Timed

The timing gear assembly is one of those things I had to sit and think about for a while (Photo 4) because I had a real hard time visualizing how these parts worked together. A detailed, exploded view of the assembly would have been very useful.

What it boils down to is, a gear on a bearing turns on a shaft that rides in a sleeve. It wasn't so bad after I finally understood what was happening. Let's go through the parts in the assembly, and I hope you will see why I had to stop and think.

To start with, there is a shaft that is threaded on the end (Photo 5). If it looks like a bolt, that's because that's what I used. Also in the photo, you can see the timing lever, which has a hollow sleeve attached. The timing lever and sleeve slide over the threaded shaft. It is important that the timing lever be movable, but at the same time, you must be able to lock the lever in place.

The timing gear has a brass bearing attached that sticks out far enough to support an insulating ring and ignition stud, as well as the cam (Photo 6). It is important that the cam and ignition stud turn with the timing gear. This small assembly slides over the sleeve attached to the timing lever. A nut on the threaded end of the shaft holds everything together.

But how does part of the assembly turn while another part of the same assembly is locked in place? Here is the secret: The sleeve sticks out just a little further than the timing gear with its brass bearing (Photo 7). The nut presses the sleeve and timing lever against the side of the engine frame. There is just enough room between the timing lever and nut for the brass bearing with its associated parts to rotate. This is what the assembly looks like in place (Photo 8).

The pushrod is literally pushed by the rotating cam and opens the exhaust valve. There is a roller on the end of the pushrod that rests on the cam. If the exhaust valve were allowed to close every intake cycle of the engine, it would continue to fire and never miss. This is where the latch-out bar comes into play.

The latch-out bar is controlled by the governor and shift collar (Photo 9). When the governor senses the engine is running too fast, it causes the latch-out bar to hold the pushrod in a position that keeps the exhaust valve from closing. If the exhaust valve doesn't close, there is no compression and the engine will not fire. There is a little more to it than that, but that is for next month.

Step 15: Fabricating Valves, Head Assembly and Mounting

Making the valves was fun. They can be made several different ways and I tried two of them. The first is to simply braze the stem to a piece of round stock and taper the edge to a 45 degree angle in the lathe. The second way is to taper the round stock while it is whole, drill the center and part it to the proper thickness. Brazing is done after everything is shaped (Photo 10). Both ways work just fine, but I like the second way better.

The only thing left to do was thread the end of the stems and seat the valves. I have cut a few threads before, but have never seated valves. The valve and valve seat have to make an airtight connection when they touch. Sounds simple, but it did take a little bit of work.

I had some really fine lapping compound used for fitting gun parts. I put a little of this on the valve and seat, then inserted the valve into the head. Next, I took a drill motor and slid the end of the stem into the chuck. While running the drill motor at 2,500 rpm, I pulled on the head, which put pressure between the valve and seat. About 60 seconds of this and I actually had an airtight connection. Is this the way you are supposed to seat a valve? I don't know, but it worked just fine. Remember, I am not a professional machinist. If I can figure out a way to make things happen, so can you!

Photo 11 shows the head in place with the valves, rocker arm and its support, as well as the pushrod. The rocker arm and rocker arm bracket are made from brass castings. Both were a simple process to mill and drill. This engine is really beginning to look like something.

Next month we'll cover the mixer and electrical connections. With a little bit of luck, we will make this thing run!

Contact engine enthusiast Richard Allen Dickey at: 246 Skyview Lane, Yellville, AR 72687; Contact the Red Wing Motor Co. at: (660) 428-2288;