My Mower with the Slant Fin Briggs 'FI' Engine

The mower shows the open gears

This view of the mower shows the open gears that drive the blade.

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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 Wisconsin.

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 overcome.

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 unique.

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' engine.

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?