Flat Head Mopar Engines
The L-Head motor, or what is more commonly known as a Flathead, was the mainstay of most auto manufacturers before World War II. A flathead motor is just that - the head is a flat, cast piece of iron that is bolted down on top of the block. The valves and the entire valve train are in the block itself. The head is relieved to allow for compression and for valve clearance, but it contains no moving parts (except the thermostat). The head is partially hollow to allow coolant to pass through to assist in cooling the engine.
Virtually all early cars were flatheads, and the flathead stuck around for a long time, but few if any flathead motors had the staying power of the Chrysler Corporation's flathead 6. As late as 1972 [Keith Windsor], this engine was being produced for industrial uses such as stationary pumps, arc welders, forklifts, and farm equipment such as harvesters and combines. Because of this, parts are still available on the shelves of better auto parts stores. I have purchased water pumps, fuel pumps, and tune up parts off the shelf for my 1948.
The flathead, because of its design limitations, was destined for doom as the fabulous fifties began to roar [though it should be noted that it may have been the best design in its early days]. The public's desire for more power prompted Chrysler to produce the legendary Hemi in 1951. Chrysler was so proud of its new engine that the front of the hood of the V8 equipped cars had a large chrome 'V' to identify the engine to all the world. The Hemi powered Chrysler 300 in 1956 was the most powerful and fastest production car in America that year, averaging 139.9 mph at Daytona.
Ross Warnell wrote:
After World War II, the 251.6 and 265.4 cubic inch engines used in Dodge medium and heavy duty trucks were equipped with sodium cooled exhaust valves and stellite seats. The hollow exhaust valve stems were filled with metallic sodium metal which would liquefy at operating temperature and transmit the heat up the stem and through the valve guide to the water jacket.
Because of the long stroke, heaps of torque were available at low rpm. My dad ran them in his propane delivery trucks. These old engines were dogs on power but would run forever, especially when fueled with LPG. Getting one started on a zero degree morning in January was an exercise in patience.
Larger trucks used another family of in-line flathead six cylinder engines. There was a 331 cubic inch and a mammoth 413 cubic inch lugger was available in the T series and up. There may have been another engine in the 370 CID range, but I am not sure about that. The 331 was highly regarded in trucking circles as a durable, hard working engine. The 413 was equipped with two single barrel carburetors and had a very large appetite for gasoline. It was noted for twisting the drive sprocket off the end of the camshaft.
Jim Benjaminson wrote:
Chrysler's move into the 6-cylinder, low price field was so unprecedented that Automotive Industries magazine devoted many pages of their February 4, 1933 issue to the machinery installed in the Plymouth plant, machinery which would not only produce the 6-cylinder engine but would cut Chrysler's cost of producing those engines to a point to make it worth while in a low priced automobile. (What makes this truly amazing is the fact that it was done in the depths of the Depression - Walter Chrysler believed in keeping workers busy and paid. Indeed, that might be one of the greatest differences between Chrysler and Henry Ford, aside from Ford's raving anti-Semitism. - Webmaster)
The big news for the year 1933, of course, was the introduction of the Plymouth 6-cylinder engine. The valve-in-block engine displaced 189.8 cubic inches from a bore of 3 1/4" and a stroke of 4 1/8". With the standard compression ratio of 5.1 the engine, which retained the Silver Dome name, pumped out 70 horsepower at 3,600 rpm. With the optional aluminum "Red Head" the compression ratio jumped to 6.5 while the horsepower increased to 76.
The engine used a redesigned water pump for better cooling efficiency, aluminum alloy pistons and had a new first as it was fitted with insert bearings on the main and connecting rod bearings, as well as the first camshaft bearing. Power was transmitted from a 9" dry clutch plate through a three speed transmission with helical gears for smooth, quiet operation.
The new engine proved to be most reliable and an economical powerplant. The basic six remained in production from its introduction in October 1932 until the cessation of 1959 model production. At that time the Valiant (which would be the shortest wheelbase Plymouth built in Plymouth history since the PC) utilized the Slant Six. The old reliable flathead six kept many an old Plymouth on the road long after its original engine had been scrapped.-the later engines were bolt for bolt swaps into the early cars. (The engine received a fully jacketed water system in 1935 which meant moving the starter slightly outboard on the bell housing. For a later engine to be put into the '33 or '34 models the bell housing had to be changed but this was unnecessary from '35 on).
1953-1954 changes (Lanny Knutson)
Under the hood of the 1953 models was the same 117 cubic inch L-head six found in Plymouths since 1942. However, this years horsepower came at an exact 100, an increase of three, thanks to a 7.1 to 1 compression ratio (up from 7:1).
Introduced-mid-year, 1954, was a 110-horsepower "Powerflow Six", a 230 cubic inch unit formerly exclusive to Dodge. The appearance of the new automatic transmissions, plus the V8 fever spreading in the car-buying public, probably dictated the move to a larger engine.
Canadian-built 1953-54 Plymouths featured the usual variations, most notably the long-block six. Manual transmission cars came with the familiar 218 cubic inch motor. When Hy-Drive, and later, Powerflite, transmissions were ordered, a new 228 cubic inch engine (formerly exclusive to the Canadian-built, American-style Coronet) was installed.
The Last Mopar Flat Head Engines
In its last civilian year, the Dodge truck 230 engine made 120 horsepower at 3,600 rpm, and 202 lb-ft of torque at a low 1,600 rpm; the compression ratio was 7.9:1. Features included exhaust-valve seat inserts and chrome-plated top piston rings.Chrysler - 1954 - 264.5 cid
DeSoto - 1954 - 250.6 cid
Dodge - 1959 - 230 cid (Note: 1959 was the last year for use in civilian cars, but Dodge publicity materials note its use in 1960 trucks, and David Youse said it continued through 1968 for the military in the Dodge M37 3/4 ton cargo truck. "The engine was essentially identical to the civilian version except that it had a waterproof ignition system and provisions to seal the crankcase so that it could run completely submerged, with intake and exaust extentions.")
Dodge Truck - 1968 - 250.6 cid* (Note: Richard Davis noted that this engine was used in the 1961-68 WM300 Power Wagon. It had replaceable hardened exhaust valve seats, full flow filtering, and full pressure oiling. It had 115 net hp at 7:1 compression until 1966, and in 1967-68 it had 125 net hp at 8:1 compression.)
Plymouth - 1959 - 230.2 cid
What made the flathead so versatile was its dependability and torque. The largest flathead six Chrysler used in its automobiles was 265.5 cubic inches that produced 218 ft/lbs of torque at 1600 RPM. So, at just off idle, this engine produced maximum torque, making it ideal for industrial use.
In comparison, the last flathead 8 was used in 1950, with 323.5 cid and 270ft/lbs @ 1600 rpm. Although the 8 was more powerful, most people found the smooth power produced by the six was sufficient, and so a vast majority of older Chryslers found today are equipped with sixes. These figures are at the rated compression of between 7 and 7.5 to 1.
The flathead eight-cylinder engine was used in a large variety of vehicles. Because it was a straight-eight (not a V8) design, the revolutionary Airflow models had to be lengthened to accommodate it.
The flathead six in my 1948 Chrysler Windsor Club Coupe is a smooth, powerful, efficient powerplant. On the highway it regularly gets from 17-19 mpg at average speeds of near 60 mph. Not bad for a car that weighs over 3600 lb (shipping weight was stated as 3463 lb)! That 'little' six is capable of speeds in excess of 100 mph (I've had it up to 95)!
Technical data above taken from The Standard Catalog of Chrysler, John Lee, 1990; and from Motor's Auto Repair Manual, 17th Edition, 1954. Note: all Mopar flathead 6 engines have the firing order of 1-5-3-6-2-4
Photo of my 1948 Chrysler's 251 cid L-Head during installation, after an overhaul.
Important swap note (Rich Hall)
This concerns the Mopar flathead six page and the part about the later engines being a "bolt for bolt swap". You just have to remember to swap enough bolts! I put a 1959 Plymouth engine (the last of the breed) in my first car, a 1948 Plymouth, in about 1968. There were obvious parts you had to swap, like the carburetor, the water pump, crankshaft pulley and generator (wide vs. narrow belts 6 vs. 12 Volts), the oil pan (to fit a different car frame), and the starter motor (6 vs. 12 Volts again.) All went well with the installation until I pushed the starter button. Klunk!! After some cyphering, I determined there was a slight change in the number of teeth on the ring gear and the 6 Volt starter bendix would not mesh!! No problem to use the old flywheel, except that now the engine was in the car and the rental hoist had been returned. Changing the flywheel in the car was far harder than when it was out.
I learned a valuable lesson, though. I later put a 1958 Studebaker Lark engine in my second car, a 1951 Bullet Nose Champion and I counted teeth when the engine was out and darned if Studebaker had not done the same thing!!