A Model Builder’s Surprises

By Staff
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Tom Thumb half scale.
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Associated 7/16 scale.

HC 6, Box 4 Aitkin, Minnesota 56431

I restore tractors, old engines and some old machinery. My
favorite part of my hobby is building scratch model engines.
I’ve built hit and miss throttle-control, inverted side shaft
and hot air.

I use mostly steel for my engines. I also use some brass
aluminum, and some cast iron. I’ve made one pattern for a
flywheel for our scale Waterloo Boy 14 HP. Ray Olson from Garfield,
Minnesota, gave me tips on how to make a pattern. He also cast them
for us. Bruce Lind-berg from Duluth, Minnesota, machined the wheels
for us. The wheels were over 10 inches in the rough. Our lathe will
only handle 10 inches. Bruce is a fine machinist.

I’m going to mention a few problems I’ve experienced, a
few mistakes and some goof ups I’ve made, how they were
corrected, and how the little engines putted away happily ever

I built a little throttle controlled engine that runs nice and
smooth. We call it our little steaming demon. On hot days, on long
runs, there is a little steam that comes from the hopper. We have
to add water once in a while. I was a little careless when I built
it. I put the governor shaft directly in line with the cam and the
business end of the rocker arm. The solution was very simple: Put a
little bend or bump on the push rod. The cam and the push rod are
inside of the engine frame, so it doesn’t show. I think this is
the only engine that has a push rod with a built-in detour.

I wanted a side shaft engine. Building one fit our budget better
than buying one, and a lot more fun! The side shaft engine I built
is not modeled to represent any special brand. When I was
assembling it I realized I may have made the connecting rod about
inch too long. This would give it too high compression. I took a
chance on leaving it that way. A timer and buzz coil was the type
of ignition used. All the bearings are oilite, including the cam
shaft bearings. Oilite doesn’t conduct electricity too well, so
the timing wasn’t positive. It would fire late, even when the
timing was set well before top dead center. By advancing the timer
a little more, sometimes it would fire on time, sometimes late and
once in a while early. When I advanced it a little more, the result
was a bent connecting rod and a broken piston. I replaced the
piston, repaired the connecting rod and changed the ignition to
regular points and coil. The result was a nice running engine.

I’m sure the oilite bearings were the problem. The current
could not reach the ground without traveling through the bearings;
with points they are grounded to the frame.

We usually travel to Texas once a year to visit our daughter and

The oil field engines interested me a lot. Of course I had to
try to build a small version of the engine and pump. This was done
about 1984. The engine ran trouble free for four or five years,
about nine shows a year, four to nine hours a day if it didn’t

The engine had Lauson engine points, a car coil and condenser.
After a few years of running it would take a notion to
‘ping’ fire early, then run normal for awhile, just ping
every few minutes. It continued to get worse. Sometimes it would
fire so early it would stall the engine. I checked all the wires
with my meter; wiggled the wires to see if I could find a bad
circuit. No luck! I tried a new set of Lauson points, which helped
a little for a couple of shows, but then it went back to its old
tricks. We happened to have a few extra sets of points bouncing
around in the glove compartment of our Ford truck. I converted the
engine to a set of flea market Ford points. Then it ran like it
should. I never did find out the cause of the occasional premature

I’ve got to reminisce a little. In 1929 we moved to
Woonsocket, South Dakota. The farm had a windmill, but even in
South Dakota the wind doesn’t blow all the time. During the
drought years, the water table must have been very low. Pumping
water by hand was very difficult. My six-year-old body could hardly
pull the pump handle down. My father bought a used IHC Tom Thumb
and a belt driven pump jack. The little dependable Tom Thumb was
used for other light jobs, too, like running the grind stone
fanning mill, etc.

You guessed it! Another engine story coming. A half scale IHC
model Tom Thumb 7 inch flywheel, 1 inch bore and stroke building
went good. No bad mistakes, goof-ups or problems.

Start up time was when the problems started. It would run for a
while but wouldn’t keep running unless I would squirt a little
extra oil in the mixer. I removed the cylinder. Machined it
over-size, took a section of 1 inch hydraulic cylinder that was
factory honed, turned down the outside to fit the engine’s
cylinder and used it for a sleeve. Then I machined piston number
two. I put two ring grooves above the wrist pin and one ring groove
below the wrist pin. Then I put in a new set of rings. The sleeve
did not help. It did not run any better. It had to be the rings or
the piston. The oil felt a little gritty when I removed the piston.
The rings showed too much wear for a couple of hours running. I
machined piston number three, this time just two rings above the
wrist pin. Then I ordered new rings from another vendor. I
installed the new piston and rings, for the third time! It started
and kept on running with no extra oil. It has been displayed at
many shows the last two summers. We pull a scale pump-jack and pump
that pumps water. Just like the ‘not so good’ old days, the
problem was bad rings.

Late summer 1995, I was thinking about building one more model.
I could think of two good reasons why I should. Number one, I enjoy
building them. Number two, I bought a new milling machine and
rotary table that I needed a lot of practice on.

I decided on a 7/16 scale Associated Hired Man, or a reasonable
resemblance of one. The bore and stroke of the original is
4’x5′. Scaled down on the model it would be 1 x 2.2. I went
2′ stroke. A little less displacement and   lower
compression makes for a smoother running engine. If you wonder why
I decided on an odd scale like 7/16, I had a few leftover parts
when I built the IHC Tom Thumb. We still had number one and number
two piston, a bunch of brand new 1 inch rings, crank shaft material
that fits the 7/16 scale Associated, plus a 1 cylinder.

Building this engine was almost without problems, except for the
head. I used one inch thick steel for a start. Machining the head
is mostly drilling for the valves intake and exhaust passages. In
this case, a spark plug hole.

I was doing real well until I took the head and matched it to
the block. It was quite obvious that I had drilled the valve
chamber on the wrong side of the head. This would put the valve
stems and springs inside of the cylinder. I made two nice little
steel plugs inch thick that fit snugly in the holes that I drilled
on the wrong side of the head. My intentions were to weld them in.
At this time I have to mention, my ‘good glasses’ were sent
back to the factory for repair. I was stuck with my old glasses
that were not good for close-up work. I thought if I was very
careful I would be able to weld the plugs in place. On my first
attempt I succeeded in welding one head bolt hole shut, but I did
get the plugs welded on one side. I cleaned up the weld slag. I
decided to completely cover the head with weld. By that time my 73
year old eyes began to focus a lot better. This time I was
successful. The weld machined up nice, and I got the valve chambers
on the right side of the head.

We still needed a home for a 10 mm spark plug, so I carefully
drilled through the top center of the head. This is the last
‘oops !’ I just nicked the exhaust passage so the plug hole
and exhaust were connected. I sealed this goof-up with a brass plug
well riveted in, and smoothed out, then changed the spark plug
position. It is located on the edge of the head, similar to the
location of the spark plug on a Fairbanks-Morse dishpan flywheel

The little engine survived all of its head surgery. None of the
scars show it is covered with bright red paint. November 10, 1995,
with my wife, Mary, sitting in the cheering section, about 15 or 20
minutes of tinkering with it, the little Associated was running on
its own!

The good optician fitted me with a fine pair of glasses, so now
I’m able to read fine print and should be able to see where
I’m welding.

I plan to build one more engine next year. Maybe 1 inch bore, 1
stroke, about 5 inch flywheels. I just happen to have some material
around my shop that can be used for an engine that size.

I have to thank my wife and best friend for 49 years for her
support. She enjoys the tractor and engine shows and also helps
care for the tractors and engines. She keeps the camper well
stocked with food and supplies. She deserves many more red roses
than I bring her. Thanks, Mary!

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