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
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
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
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
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
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
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; firstname.lastname@example.org Contact the Red
Wing Motor Co. at: (660) 428-2288; www.modelengines.com