My Mower with the Slant Fin Briggs ‘FI’ Engine

By Staff
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This view of the mower shows the open gears that drive the blade.
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Crank side of the mower showing the Briggs 'FI' engine.
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The crank is hanging on its bracket on the handle. Note the roller that drives the mower.
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1927 Lawn mower ad.
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This view of the mower shows the open gears.

7574 S. 74 Street Franklin, Wisconsin 53132

When I first saw the photo of the old lawn mower, with a slant
fin Briggs ‘FI’ engine to power it, I knew that I wanted
it. It would increase my power mower collection to 70, but how
could I pass it up? The serial number on the engine dated it to
1927. There was no manufacturer’s name on the mower, but it
looked complete. The first problem to overcome, however, was the
fact that the mower was in northeast Pennsylvania and I am in
Wisconsin and this was January. I paid for the mower and in June
our family was going to the Coolspring, Pennsylvania Show anyway,
so a trip across the state of Pennsylvania was in the plans to
retrieve the mower. It is a six hour drive from Coolspring to
Stroudsburg, but I thrilled my wife with stops along the way, to
look at other engines. The poor mower was mostly rusty, but at
least it was complete. I removed the handle and gas tank and loaded
it into our already full Taurus wagon for the trip back to

When I had the mower home, I photographed the mower from every
angle possible. This was a lifesaver later on. I highly recommend
taking many photographs of a project before and during disassembly.
They are great to refer to later. You never know when you will be
looking at one of the photos with a magnifying glass to find out
about one detail (was the bolt head or nut on the outside?). Also,
I made sketches of the mechanical linkages and dimensions where the
different parts were placed on the shafts.

Upon disassembly, I found that the sheet metal deck was beyond
repair. Also, several generations of mice had taken up residence in
the sheet metal drive roller and their urine rusted through the
sheet metal. One cast iron clutch dog was broken and the loose
parts missing. One gear and axle in the main gear case was worn
horribly in the axle hole from lack of lubrication. When designed,
it was a cast iron gear running on a steel shaft with absolutely no
way to get oil to the axle. One brass chain sprocket was worn
beyond future use. Stupid me broke the magneto plate on the Briggs
FI engine while disassembling it. These things could all be

I hired a local sheet metal contractor to bend me a new deck and
roll the sheet metal for the roller and braze them to the cast iron
ends. Since I do foundry work as another hobby, I used the good
clutch dog as a pattern and cast up two (one extra) cast iron
replicas. I machined one, so that I now had a pair. I bought a new
gear and machined it for an ‘Oilite’ oil impregnated bronze
bushing and machined a new axle. I had to create a replacement
brass sprocket by machining one from brass plate. I also learned
that in 1929, woodruff keys were made in different sizes than they
are now. You would not believe the number of people who think I am
crazy, restoring old iron!

I always look at ads and various papers at the shows, looking
for old lawn mower literature, I found a 1929 ad for my mower! It
was a Cooper, made in Marshalltown, Iowa. I know that they made
mowers into the ’60s and built a mower called the ‘Cooper
Klipper.’ Somehow I found out that Cooper is still in business,
although not building mowers anymore. I contacted them and was
referred to a retired Mr. Cooper. From him I was able to learn a
little about my mower.

It seems that in 1927 they hired a man from Wisconsin to design
a power mower for them to start manufacturing. I have one of the
very early examples of this mower, with the open gears to drive the
blade. Not many of this style were made before they changed to a
chain drive to turn the blade and casters instead of solid front
wheels. The chain drive on the later mowers had a cover over the
chain and sprockets. The open gearing and shaft makes this mower

The people at Cooper had never seen one of their mowers that was
this old. Unfortunately, they had no photos or drawings anymore.
There was no way that they could tell me why the red pin striping
was discontinued. They were, however, able to confirm that the
color was dark green, just as I suspected when I stripped off the
coats of paint (where there was paint left).

Assembly of the mower went fine. I sandblasted every part and
primed it with Rust-Oleum brown primer. The original paint color
was evident in places that were never exposed to sunlight. The rest
had been repainted at least once with a darker color, or was rusty.
Where bolt heads could be seen, I cleaned and reused the original
bolts, because bolts of today look different than those of 1929.
Almost every bolt on this mower was fine thread. Meanwhile, the
‘FI’ engine was going back together at the same time. I had
sandblasted the crank-case, head and oil sump; then cleaned, primed
and painted the parts.

Before sandblasting a part such as the cylinder, plywood covers
and gaskets have to be made to cover every opening, so that no sand
gets inside. Any small openings are plugged with silicone bathtub
caulk, wood dowels, or both. Some openings had to have wood plugs
turned to size on the lathe. All threaded holes had a machine screw
or bolts installed. After sandblasting, the part is then blown out
with compressed air and then pressure washed inside and out with
hot soapy water. I take all these precautions to make sure no sand
gets in the part.

The exhaust valve guide on the head was broken off, so I milled
a counter bore where the valve should be and machined a steel guide
that could be pressed into place. With help and a new valve, from
CPC Reproductions, the head was as good as new. Chuck from CPC
Reproductions was very helpful in supplying missing or broken parts
and gaskets, rings, manuals, etc. for the Briggs ‘FI’
engine. I have got to thank Chuck Camara (CPC Reproductions) and
Gary Pegelow of Wisconsin, for putting up with my endless questions
about this Briggs engine.

These Briggs engines with outside rocker arms have no timing
marks on the timing gears. There is a method of setting the timing,
described in the manual. Even after setting the gears to what I
thought was right, I still wondered if I was in the correct tooth.
By checking other engines, I came up with a simple check. Using a
3/16‘ metal rod and a metal marking pen,
insert the rod vertically down the spark plug hole until it touches
the piston. Rotate the flywheel in the direction of rotation for
the engine. On the power stroke, while pressing down on the exhaust
valve push rod with your fingers, mark the rod even with the top of
the spark plug threads exactly when the rod begins to lift. Then
mark the rod at the bottom of the stroke. The distance between the
two marks should be about .’ The push rod should begin to lift
when the piston is ‘ before bottom dead center. This also works
on an ‘FH’ engine. One tooth difference should make a big
difference in where the valve opens.

I acquired another magneto plate, which also holds the main
bearing. These old cast aluminum alloy, or ‘white metal’
die castings, tend to swell up with age, so it is common that they
are too large to fit in the hole in the crankcase. I had to remove
.oo4′ on the entire circle, so that it would slip into the
opening. Since this part is too fragile to chuck in the lathe to
take a cut, I very carefully filed the holder down to size with a
hand file. I then machined new brass rivets to hold this plate to
the flat, sheet metal shroud and riveted it back in place, being
careful not to crack the ‘new’ plate at a rivet hole.

The gas tank had a leak where the outlet plate was soldered to
the tank. I cleaned the tank by sandblasting inside and out and
then soldered the outlet plate. It was easy to solder because the
metal was clean from the sandblasting. I coated the inside of the
gas tank with the gas tank sealer sold by Lee Pedersen and then
left the tank outside in the sun to bake.

As a spark plug collector, I take notice of the plugs that are
in the old engines. I didn’t really want to install a new
Champion plug in my 1927 restored engine, right in plain view of
everyone. The different brands of pink colored plugs have always
intrigued me. They contain Polonium, which was one of many gimmicks
used by old plug makers to trick the public into thinking that
their plug was the best. I purchased a ‘new old stock’
Firestone Polonium (pink) spark plug from Bob’s Small Engine
Service and installed it in the engine.

After the mower was finally assembled and the engine mounted and
coupled to the gear drive, I put gas in the gas tank and checked
for leaks. I then put the crank on the shaft and cranked the engine
over, with my finger on the air intake hole as a choke (these
engines did not have a choke). When I took my finger off the air
intake, the old slant fin ‘FI’ engine started and ran fine.
That is the moment where pride takes over and you call your wife
(and anyone else in hearing distance) to see your new toy run. I
threw in the blade clutch and stood back to admire my work.

As this mower will be displayed running at shows, and not
cutting grass, I moved the bed knife back so that it doesn’t
touch the blade. Then I adjusted the blade drive clutch so that it
just barely has power to turn the blade. That way if someone at a
show sticks his foot in the blade, the clutch will slip and the
blade will stop without hurting him badly. These old mowers are fun
to watch, but one can’t be too careful with the public around,
many of which are too young to have ever used a reel mower.

This mower has an open gear drive on the left side of the mower
to drive the blade. The small gear can be moved to two positions on
the large gear, to turn the blade at two speed ranges. The same
gear can be moved to the other side of the large gear to turn the
blade in reverse for honing the blade against the bed knife to
sharpen the blade. This is all nice to see operate and makes for an
interesting mower.

Many of the old lawn mower ads show a man mowing the grass in
front of a large house or mansion. Probably in the 1920s, a person
would have to be wealthy to afford a power mower. The particular ad
for my mowers shows a young woman in high heels and a dress mowing
the front lawn of a mansion. Since I didn’t know anybody that
either looked like that, or would dress like that for a photo with
my mower, I knew that I would have to pose for the photo myself. I
wanted to sort of duplicate one of these old photos with my
restored mower. My oldest boy found the ideal building for my
photo. It is the club house for a county golf course, which has a
large lawn. Originally, the building was a large private house,
built in 1892 and acquired by the county in 1919, when the land was
turned into a golf course. In researching the old ad photos, the
men wore a white shirt, tie and dark pants (blue jeans were not
popular in 1927). I dressed as close as I could to the period
clothing for the photo that culminates the rebuilding of the 1927
Cooper Power Lawn Mower with the Briggs slant fin ‘FI’

This mower was exhibited at several shows this year and I have
been kept busy answering questions about it. Also, that pink plug
has attracted quite a bit of attention. I enjoy the old lawn mowers
and everyone, old or young knows what they are used for. After all,
isn’t using a lawn mower everyone’s favorite Saturday
morning job?

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