Vintage Briggs And Stratton Identification
Article by Mark Trotta
Every time I visited my friend's workshop, I noticed the old Briggs flathead he had propped up on a shelf. I wondered how old it was, and if he would ever part with it.
After dismounting some worn tires off a set of old truck wheels for him, he said, "How can I repay you?"
"How about selling me that old Briggs motor over there?"
"Oh, you can have that."
So, I became the proud owner of a non-running, older-than-me, vintage Briggs & Stratton flathead. With the exception of the missing gas tank and air cleaner, the engine was complete and original. I'm hoping that the missing parts can be easily located, but first, I had to find out what year and model the motor was.
Identifying Vintage Briggs & Stratton Engines
On vintage B&S motors, an ID plate was mounted to the blower housing next to the intake port. Later Briggs engines had ID numbers stamped into the blower housing, on the carb side near the top outside edge.
The ID tag is the easiest way to identify a vintage Briggs engine.
Missing Identification Tag
When you encounter an old engine with no ID tag or numbers on the housing, the next steps are checking if the block is aluminum or iron, and by counting the cylinder head bolts. To determine if an engine block is aluminum or cast iron, see if a magnet will stick to it.
Typically, aluminum engines will have ID numbers stamped into the blower housing.
How Can I Tell It's The Original Blower Housing?
A blower housing with decals and ID can easily be swapped from one engine to another, so you don't really know what you have until you remove the housing and the cylinder head. Measuring the bore and stroke of the engine is the best way to tell what engine you have.
If you're not certain it's the original cover, you won't really know what you have until you measure the engine bore and stroke. Opening up the motor helps solve other mysteries, too, like if an overhaul or modifications have been done.
Identifying Cast-Iron Briggs Engines
- 6 head bolts - cast-iron models N, 5, 6, and 8
- 7 head bolts - cast-iron models 9, 14, and 19
- 9 head bolts - cast-iron models 23, 230000, 240000, 300000, and 320000
Identifying Aluminum Block Briggs Motors
- 7 head bolts - aluminum models 15 cubic-inches or less
- 8 head bolts - aluminum models 17, 19, 22, and 25 cubic-inches
This old Briggs motor is cast-iron and has 6 head bolts, so it's either a model N, 5, 6, or 8. To help narrow that down, I measured the cylinder bore and stroke. The piston bore was 2-1/4 (2.25) inches and the stroke length was 2 inches.
Briggs & Stratton With 2" Bore
- 2.00" Bore x 1.5" Stroke - Model Series 5 (1950-1957)
- 2.00" Bore x 1.5" Stroke - Model Series 5S (1949-1957)
- 2.00" Bore x 2.00" Stroke - Model Series N (1940-1954)
- 2.00" Bore x 2.00" Stroke - Model Series 6 (1952-1957)
- Above w/aluminum block - Model Series 6B (1953-1958)
- Above with suction-style carburetor - Model Series 6BS
- 2.00" Bore x 2.00" Stroke - Model Series 6H (1950-1956)
- 2.00" Bore x 2.00" Stroke - Model Series 6S (1949-1957)
What The Numbers And Letters Mean
- model number (5 or 6) is c.i. displacement
- the letter "S" is for suction carburetor
- the letter "B" is for aluminum block
- the letter "H" is for horizontal crankshaft
Briggs & Stratton With 2-1/4" Bore
- 2.25" Bore x 2.00" Stroke - Model Series 8 (old) (1949-1953)
- 2.25" Bore x 2.00" Stroke - Model Series 8 (new) (1952-1957)
- 2.25" Bore x 2.00" Stroke - Model Series 9 (old) (1948 - ? )
- 2.25" Bore x 2.25" Stroke - Model Series FI (1927-1933)
After measuring a 2-1/4" bore with a 2" stroke and having a 6-bolt head, this engine is either a Briggs model 8 or model 9. The horizontal-split cast iron block and aluminum base helped me determine that this engine was a new style 8 series.
Briggs 5S vs 6S
Briggs 5S (five-S) and 6S (six-S) engines are fairly common. The main difference between the two is the length of the piston stroke (1.50" vs 2.00"). These engines were found primarily on lawn and garden equipment, but also on vintage scooters and minibikes. A 6B-S looks identical to a 6S, but it has a cast aluminum block instead of cast iron.
Read: Briggs & Stratton 5S Engine
Briggs & Stratton 60000 Series
In 1957, the 5-series engines were discontinued, and the 6-series were replaced with the "60000" series, which had a different bore and different stroke.
- 2.31" Bore x 1.50" Stroke - Model Series 60000 (early)
- 2.38" Bore x 1.50" Stroke - Model Series 60000 (late)
Briggs & Stratton 80000 Series
- 2.38" Bore x 1.75" Stroke - Model Series 80000
- Other models in this series include 81000, 82000, and 83000
Most vintage Briggs motors built before 1965 will have a date code stamped on the flywheel and/or magneto plate. The last two digits of the year are shown in one casting, followed by a letter representing the month. The months are coded in letters; for example, A = January, B = February, etc.
Briggs & Stratton With 2-1/2" And Larger Bores
Briggs & Stratton PB Series
- 2.50" Bore x 2.50" Stroke - Model Series PB (1923 to 1935)
Briggs & Stratton 90000 Series
- 2.56" Bore x 1.75" Stroke - Model Series 90000
Briggs & Stratton 100000 Series
- 2.50" Bore x 2.12" Stroke - Model Series 100000 and 100900
Briggs & Stratton 100700 Series
- 2.56" Bore x 1.94" Stroke - Model Series 100700
Briggs W Series Engines
Primarily designed to power washing machines, the WM motor was produced from 1936 to 1941. The visual identifier is the spark plug; it mounts horizontally into the cylinder head. Other versions of this motor were the WMI and WMG.
An improved version of the WM, the WMB and WI engines, were produced from 1938-1957. These motors have the spark plug mounted vertically in the cylinder head.
Round vs Flat Air Cleaner
Another age identifier is the engine air filter. Early Briggs engines had a round oil-bath filter secured by a wing nut on top of the carburetor. The bottom of the canister gets filled with oil.
The oil-bath filters were phased out in the mid 1960s, and replaced by the flat, kidney-shaped gas tank shown here.
Briggs Stratton Logo
Throughout it's history, Briggs & Stratton had a variety of logos with different shapes and colors. The first gold logo was used from 1948 to 1963. Early examples had a brass ID tag on the blower housing and an external crankcase breather.
Appearing on the original gold logo decal is the name "Briggs & Stratton" with "Milwaukee, Wis., U.S.A." below it. The middle of the decal has the words "4 CYCLE" on the top mast and the words "GASOLINE ENGINE" with "MADE IN U.S.A." on the bottom mast.
A second gold logo was seen from 1963 through 1976.
Although similar to the early logo, the wording was arranged differently. The name BRIGGS & STRATTON was written in a new logo type, and engine horsepower rating was included above the gold logo. The city of location was in the middle as before, but the patent numbers were eliminated.
Some Briggs engines produced in the seventies were factory fitted with the earlier logo, so there are exceptions to the early/late logos.
Mid 70's and Up
The red, white and black Briggs & Stratton logo began in 1976 and is in use to the present day. The logo hasn't changed much since, although the wording on the top and bottom sections of the mast were removed in 1985.
Although it's been 20+ years since production ended, these little motors are still very popular.
The 5-horsepower Briggs flathead is so popular that there are racing classes based on that engine.