How to Identify a Mercury Flathead

by Floyd Drake III

Named after its flat cylinder heads, Ford Flathead V-8 engines, developed in 1930 to 1931, were manufactured from 1932 to 1954, and although there were five different Flathead sizes, Mercury vehicles were only equipped with the 239 cubic-inch engine from 1939 to 1948, and the 255 cubic-inch motor from 1949 to 1954. Except for 1946 to 1948, when both brands used the 239, Ford always used the smaller engine size. Identification of Mercury Flatheads requires locating the engine code, which determines the date of manufacture.

Step 1

Locate the engine number. The Flathead's serial number is located on the transmission flange at the rear of the engine block. Look at the top of the bellhousing. From 1938 to 1948, the bellhousing was cast as part of the engine block, and is part of the engine block. The serial number is two to four positions, and may have both letters and numbers. An example, "91A" identifies the motor as a 1931 85-horsepower Flathead.

Step 2

Find the engine serial number on 1949 to 1954 Flatheads. These Flatheads have detachable bellhousings, with the serial number located on a flat surface near the intake manifold gasket face. Look towards the rear of the block on the passenger's side. According to the Flathead Fords and Nostalgia Drag Racing website, the serial number is three to four positions and includes both letters and numbers. Decode the letters according to this key: M=0, G=1, B=2, L=3, A=4, C=5, K=6, H=7, T=8, R=9, S=10, E=11, F=12. The code "B25L" was manufactured on February 25, 1953.

Step 3

Reference the Flathead serial number to Van Pelt Sales' Early Ford Serial Numbers chart (see Resources). This listing identifies the serial numbers for Ford, Lincoln and Mercury Flathead engines in a year-to-year format.

Step 4

Differentiate a Mercury Flathead from a Ford Flathead visually. According to Van Pelt Sales, the only visual method of differentiating Mercury and Ford Flatheads is to look at the front counterweght of the crankshaft. Mercury crankshafts have a longer stroke and are identified by a dimple on the top of the crankshaft counterweight.

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