AMC Straight-6 engine

The AMC straight-6 engine is a family of straight-six engines produced by American Motors Corporation (AMC) and used in passenger cars and Jeep vehicles from 1964 through 2006. Production continued after Chrysler acquired AMC in 1987.

American Motors' first inline-six engine was a legacy model initially designed by Nash Motors; it was discontinued in 1965. A completely new design was introduced by AMC in 1964. The engine evolved in several displacements and underwent upgrades. Vehículos Automotores Mexicanos (VAM) also manufactured this family of six-cylinder engines, including a version available only in Mexico.

A new 4.0 L engine was introduced by AMC in 1986 and became the final version of AMC inline sixes. It is regarded as one of the best 4x4 and off-road engines. This engine was produced by Chrysler through 2006.

Among "classic American engines, the AMC straight-six stands as a testament to smart engineering and enduring performance".

Predecessors

The straight-six engine lineage at AMC goes back to Nash Motors. An economy-focused engine debuted in the 1941 Nash Ambassador 600 model. Its initial displacement of was subsequently increased to and finally to in 1952.

After Nash merged with Hudson to form AMC in 1954, efforts continued to enhance performance and meet evolving market demands. The engine's architecture underwent a significant transformation for the 1956 model year, transitioning from a flathead (L-head) side-valve configuration to an overhead valve (OHV) design. This modernization aimed to improve engine efficiency and power output. The flathead version was reintroduced in 1958, serving as the base economy engine for the newly launched Rambler American compact car. This dual-engine strategy persisted until 1965, catering to performance-oriented and economy-minded consumers.

To reduce vehicle weight and enhance fuel efficiency, AMC introduced a die-cast aluminum block version of the OHV engine in 1961. This innovative approach resulted in a significant weight reduction, with the aluminum engine weighing , compared to its cast-iron counterpart's . This aluminum engine was produced through 1964, showcasing AMC's engineering prowess and willingness to experiment with advanced materials.

While not known for high performance, this engine was known for reliability. This engine was also used in marine applications.

Modern Era

American Motors introduced a groundbreaking inline-six engine in 1964. It featured a short-stroke design and a robust seven-main bearing crankshaft with an overall design to provide good torque at low RPMs. This engine, a testament to AMC's engineering, enjoyed a remarkable production run that continued under AMC and Vehículos Automotores Mexicanos (VAM) as well as by Chrysler until 2006. Its enduring legacy and reputation as a reliable and rugged engine, particularly in off-road applications, has solidified its position as superior to Chrysler's Slant-6.

Initially marketed as the "Torque Command" engine, the inline-six represented AMC's first genuinely modern six-cylinder engine. Road tests conducted by ''Consumer Reports'' lauded the engine as "a very smooth and quiet engine, which should give good performance."

To commemorate the engine's launch in May 1964, AMC produced 2,520 special "Typhoon" editions based on the Rambler Classic two-door hardtop. These distinctive vehicles featured the 8.5:1 compression ratio engine, a striking Solar Yellow exterior with a Classic Black roof, and "Typhoon" badging in place of the standard "Classic" script. Notably, all other Rambler Classic options, except alternative engine choices, were available on the Typhoon edition.

For the 1965 model year, the 232 engine superseded the aging Nash OHV inline-six in the Classic and Ambassador models. This marked the return of a six-cylinder engine in the Ambassador line since 1956, reflecting AMC's commitment to offering a wider range of powertrain options.

In 1966, AMC expanded its six-cylinder lineup by introducing the version of the 232 engine. This smaller variant replaced the OHV and L-head engines across AMC's passenger car lineup.

Both the 199 and 232 engines shared a bore, differing only in stroke: for the 199 and for the 232. The 199 engine was discontinued in 1970, while the 232 continued production alongside the larger engine, which the increase in displacement was achieved by employing a stroke crankshaft and a slightly taller engine block.

More stringent emission control regulations, coupled with the growing weight of vehicles due to safety mandates, led to a gradual decline in engine power output, ultimately resulting in the discontinuation of the 232 in 1979.

199

The engine was produced from 1965 through 1970.

Navarro Indy

Barney Navarro selected the 199 AMC engine to power a race car for the Indianapolis 500. Navarro had previously applied turbocharging to a variety of engines that led to the 199 engine's Indy-related application "based on a Stone-Age-strong Nash 6."

This engine had not been used in an IndyCar. However, Navarro selected it "due both to its strong bottom end and thick cylinder walls." For the first Indy attempt, Navarro designed a fuel-injection system, a unique head, and a single turbo to achieve at 6000 rpm. This was with the stock block featuring seven main bearings and large journal sizes, while the second block was drilled for four-bolt caps. Successive engines incorporated double turbochargers to produce .

Navarro fielded a 1964 Watson car with the AMC 199 engine for three years at the Indianapolis 500. However, the #50 Navarro-Rambler never qualified due to problems with drivers and with the suspension of the cars. The car was also entered at the 1971 IndyCar "Rafaela 300" season opener in Argentina. This was the car's fourth actual race start, and it began at 19 on the starting grid. Dave Strickland drove it for 45 laps. This car was then driven by Les Scott in practice for the 1971 Indy 500 race. The following year, another attempt to qualify was with Leon Sirois as the driver.

An auction was held on 14 July 2005, to clear the remaining contents of the Navarro Engineering shop in Los Angeles. A private collector purchased a complete Navarro engine for $15,000.

* Rambler Classic (1965–1966, fleet cars only)
* Rambler American/AMC Rambler (1965–1969)
* AMC Hornet (1970)
* AMC Gremlin (1970)
* VAM Rambler American (mid 1965–1969) U.S. equivalent — AMC Rambler American and AMC Rambler sedans
* VAM Camioneta Rambler American (mid 1965–1967) U.S. equivalent — AMC Rambler American wagon

232

The engine was produced from 1964 until 1979. The 232 was the base six-cylinder engine on many models through 1979, and even towards the end of its usage, it was considered reasonably modern in design.

After its midyear 1964 introduction in the "Typhoon" two-door hardtop as part of the mid-sized Rambler Classic line, the 232 engine was adapted to fit into the smaller 1965 Rambler American by using a special short water pump, an adaptive piece also used in the 1971 through 1975 Jeep CJ-5. Air conditioning was available only with the older 196 engine in the American models because there was not enough space for the compressor with the longer 232.

Through the 1970 model year, the 232 shared a deck height with the engines. Starting in 1971, AMC raised the deck height to produce the 258, and the 232 adopted the 199's longer connecting rods and shared deck height with the 258. Bore and stroke remained the same.

In 1972, the bell housing bolt pattern changed to match the larger version used on the V8 engines.

Changes for the 1976 model year included fuel economy improvements that reduced emissions and warmup time. This was accomplished by reshaped carburetor air passages that pushed the fuel efficiency of a 232-equipped AMC Gremlin to as tested by the United States Environmental Protection Agency, compared to in 1975.

*Rambler Classic (1964–1966)
* Rambler American/AMC Rambler (1964–1969)
* Rambler/AMC Marlin (1965–1967)
* Rambler/AMC Ambassador (1965–1970)
* Rambler/AMC Rebel (1967–1970)
*AMC Javelin (1968–1974)
* AMC Hornet (1970–1977)
*AMC Gremlin (1970–1978)
*AMC Matador (1971–1974)
*AMC Pacer (1975–1979)
* AMC Concord (1978–1979)
* AMC Spirit (1979)
*Jeep CJ (1972–1979)
*Jeep Cherokee (1974–1979)
*Jeep Wagoneer (1965–1971)
* Jeep J-Series (1965–1970)
* Jeep Commando (1972–1973) (1976 in Spain)
*International Scout (1969–1971)
* International Light Line pickups/Travelall (1968–1971)
*VAM Rambler American Hardtop (1965) U.S. equivalent AMC Rambler American 440H hardtop
*VAM Rambler American Rally (1969–1971) U.S. equivalent 1969 AMC Rambler Rogue sedan instead of hardtop and 1970–1971 Hornet X
*VAM Rambler American (1968–1972) U.S. equivalent AMC Rambler American sedans and AMC Hornet sedans
*VAM Camioneta Rambler American (1968–1972) U.S. equivalent AMC Rambler American wagon and AMC Hornet Sportabout
*VAM Rambler Classic 660 (1965) U.S. equivalent AMC Rambler Classic
*VAM Rambler Classic 770 (1966–1969) U.S. equivalent 1966 AMC Rambler Classic sedans plus AMC Rebel four door sedan
*VAM Rambler Classic SST (1967–1969) U.S. equivalent AMC Rebel hardtop
*VAM Javelin (1968–1969) U.S. equivalent AMC Javelin
*VAM Gremlin (1974–1976) U.S. equivalent AMC Gremlin

252

The engine was produced by AMC's Mexican subsidiary Vehículos Automotores Mexicanos (VAM) beginning in 1969 and was dropped after 1972, replaced with AMC's 258 for the 1973 model year onward. This was similar to a 232 in stroke with a larger bore, for an actual displacement of . It was produced in VAM's Lerma, Estado de México engine plant.

Output for 1972 Rambler American Rally model ( gross):
*Horsepower at 4600 rpm
*Torque at 2300 rpm

Engine dimensions:
*Compression ratio 9.5:1
*Intake valve diameter
*Exhaust valve diameter
*Connecting Rod length
*Deck height
*Bore
*Stroke

*VAM Javelin (1969–1970) U.S. equivalent — AMC Javelin
*VAM Rambler Classic SST (1969–1971) U.S. equivalent — AMC Rebel hardtop and AMC Matador hardtop
*VAM Rambler Classic 770 (1970) U.S. equivalent — AMC Rebel sedan
*VAM Rambler Classic DPL (1971) U.S. equivalent — AMC Matador sedan
*VAM Rambler American Rally (1972) U.S. equivalent — AMC Hornet Rallye X

258

The was produced from 1971 through 1990. It featured an undersquare bore and stroke; it was otherwise similar to the 199 and 232 (Note: Starting in the mid-1970s the 258's bore and stroke was changed to a bore over a 3.75" stroke. This allowed one block to be used for both the 232 and 258 and the same crankshaft blank could be milled to the two different strokes).

This engine is considered reliable, inexpensive, and torquey. Later 258 models (starting with the 1980 model year for California AMC Concords and Spirits, 1981 for California Jeeps, California Eagles, and 49-state Concord and Spirits, as well as in 1982 for 49-state Eagles and all other applications) are equipped with AMC Computerized Engine Control (CEC) system. For 1981, as part of a weight reduction program (aluminum intake manifold, plastic rocker arm cover), the crankshaft was changed from a twelve counterweight design to four, saving approximately .

This engine also found use in farm/industrial applications such as the International Harvester 4000 swather.

* AMC Hornet/ Concord/Eagle (1971–1988)
*AMC Pacer (1975–1980)
*AMC Matador (1971–1978)
*AMC Gremlin and Spirit (1971–1983)
*International Scout and Light Line trucks (1972–1980)
*Jeep CJ (1972–1986)
*Jeep Cherokee and Wagoneer (1972–1986)
* Jeep J-Series (1971–1988)
*Jeep Wrangler (1987–1990)
* Jeep Commando (1972–1973)
*VAM Rambler American (1973–1974) U.S. equivalent — AMC Hornet sedans
*VAM Rambler American Rally (1973–1974) U.S. equivalent — AMC Hornet X sedan instead of a hatchback
*VAM Camioneta Rambler American (1973–1974) U.S. equivalent — AMC Hornet Sportabout
*VAM American (1975–1983) U.S. equivalent — AMC Hornet sedan base model and AMC Concord sedan base model
*VAM American Rally (1975) U.S. equivalent — AMC Hornet X sedan instead of a hatchback
*VAM Camioneta American (1975–1983) U.S. equivalent — AMC Hornet Sportabout and Concord base model wagon
*VAM American ECD (1975–1979) U.S. equivalent — AMC Hornet DL two and four-door sedans and AMC Concord DL/Limited four-door sedan
*VAM Gremlin X (1976–1982) U.S. equivalent — AMC Gremlin X and AMC Spirit sedan X model equivalent
*VAM Gremlin (1977–1983) U.S. equivalent — AMC Gremlin and AMC Spirit sedan base model

282

The engine was produced by AMC's Mexican subsidiary Vehículos Automotores Mexicanos (VAM) beginning in 1971 through 1986. This was similar to a 258 in stroke, cast with a larger bore, larger than the 258, making . All VAM 282s from 1971 through 1978 were still advertised with an output measured using the gross rating system that was last used under AMC in 1971. The 1979 through 1983 engines were measured under the new net rating system. All units were produced in VAM's engine plant located in Lerma, Estado de México.

The 282, which had a larger bore, is considered the ancestor of the  L stroker engine, where it is common for the engine rebuilder to use an AMC 258 crankshaft in a Jeep 4.0 cylinder block – a 4.5 uses the stock AMC 258 connecting rods (with stock or .020 overbore using aftermarket pistons). In contrast, the 4.6, 4.7, and 5.0 strokers use the 258 cranks, but retain the 4.0 connecting rods.

Output for 1971–1973 models (gross):
* Horsepower at 4400 rpm
* Torque at 2200 rpm
* Compression ratio 9.5:1

Output for 1974 models (gross):
* Horsepower at 4400 rpm
* Torque at 2200 rpm
* Compression ratio 8.5:1

Output for 1975–1976 models (gross):
* Horsepower at 4400 rpm
* Torque at 2200 rpm
* Compression ratio 7.7:1

Output for 1977–1978 models (gross):
* Horsepower at 4400 rpm
* Torque at 2200 rpm
* Compression ratio 8.0:1

Output for 1979–1981 Standard models (net):
* Horsepower at 3800 rpm
* Torque at 2200 rpm
* Compression ratio 8.0:1

Output for 1979 American 06/S and 1980–81 Rally GT models (net):
* Horsepower at 4200 rpm
* Torque at 2600 rpm
* Compression ratio 8.5:1

Output for 1982–1983 models (net):
* Horsepower at 4000 rpm
* Torque at 1800 rpm
* Compression ratio 8.5:1

Engine dimensions:
* Intake valve diameter
* Exhaust valve diameter
* Connecting rod length
* Deck height
* Bore
* Stroke

*VAM Javelin (1971–1973) U.S. equivalent — AMC Javelin
*VAM Classic DPL (1972–1976) U.S. equivalent — AMC Matador Sedan
*VAM Classic Brougham (1972, 1974–1976) U.S. equivalent — 1972 AMC Matador hardtop and AMC Matador Brougham coupe
*VAM Classic AMX (1974–1976) U.S. equivalent — AMC Matador X coupe
*VAM Pacer (1976–1979) U.S. equivalent — AMC Pacer coupe
*VAM Pacer X (1979) U.S. equivalent — AMC Pacer X coupe
*VAM American Rally (1976–1977) U.S. equivalent — AMC Hornet X sedan instead of hatchback
*VAM American Rally AMX (1978–1979) U.S. equivalent — AMC Concord AMX hatchback
*VAM American GFS (1977–1982) U.S. equivalent — AMC Hornet DL two-door sedan plus AMC Concord DL and Limited two-door sedans
*VAM Camioneta American Automática (1977–1978) U.S. equivalent — AMC Hornet DL wagon and AMC Concord DL wagon, both with automatic transmission
*VAM Camioneta American DL (1979–1983) U.S. equivalent — AMC Concord DL and Limited wagons
*VAM American 06/S (1979) U.S. equivalent AMC Concord two-door sedan, high-performance limited edition
*VAM American ECD (1980–1982) U.S. equivalent — AMC Concord DL and Limited four-door sedans
*VAM Rally AMX (1980–1983) U.S. equivalent — AMC Spirit GT coupe, standard version
*VAM Rally GT (1980–1981) U.S. equivalent — AMC Spirit GT coupe, high-performance version
*VAM Rally SST (1981) U.S. equivalent — AMC Spirit Limited coupe
* VAM Lerma (1981–1982)
*VAM Jeep Wagoneer (1972–1983) U.S. equivalent — AMC Jeep Wagoneer
*Renault/VAM Jeep Grand Wagoneer from 1984 through 1986 (U.S. equivalent — Jeep Grand Wagoneer)

4.0

American Motors began developing the engine in 1984 and it was completed in just 26 months using many off-the-shelf components while featuring, among others, additional strength, improved combustion chamber, port setup, and cam profile. The total weight of the new engine was , only one pound more than the 258 six despite its heavier-duty components and parts. The cast aluminum valve cover featured 15 bolts, the industry's most, to achieve a positive seal.

The new engine, which was introduced in 1986 for the 1987 model year, was a further evolution of AMC's 258 six. It had a bore and a stroke giving it a displacement of . Connecting rod length was 6.125 inches — similar to the discontinued 199 which was phased out in 1970.

The 4.0 L is one of AMC's best-known engines. It was one of four AMC engines kept in production when Chrysler bought AMC in 1987. Chrysler engineers continued to refine the engine to reduce noise, vibration, and harshness. The last in the line of the AMC inline sixes, the 4.0 L is regarded as one of the best Chrysler 4x4 off-road engines. A ''Motor Trend'' long-term test of a 1997 Cherokee XJ noted "this long-lived OHV powerplant has a reputation for getting people where they need to go" as well as "much love expressed by owners for the torquey 4.0-liter/190-horsepower inline six." The engine is known for longevity, and can sometimes go more than without rebuilding. The vibration dampener (harmonic balancer) usually gives out after 300,000 miles, where it is common for the rubber insulation to deteriorate where a service replacement is warranted. Described "as reliable as a block of wood" by ''Popular Mechanics'' and ranked first among "the ten best car engines they stopped making in the past 20 years," the 4.0 L should run 200,000 miles before a rebuild is even expected and it is also able to "suffer running conditions that'd kill most motors." It is rated by SlashGear's "most reliable inline six-cylinder engines ever". The 4.0 "has a very good reputation for dependability and durability. It's generally considered indestructible."

When introduced, the block-mounted oil filter check valve was eliminated on the 4.0 (along with the 2.5 and 4.2 L engines manufactured after September 1986) when AMC engineers standardized their oil filters. The pre-1987 engines had an oil filter adapter with 3/4 (cylinder block end) and 13/16 threads (which used a GM oil filter common to Buick, Oldsmobile, Pontiac, and Cadillac V8 engines). In contrast, the 1987 through 2006 engines were initially fitted with a metric thread filter (later revised in 1991 for the common 3/4 threaded Mopar and Ford V8 oil filter; the oil filter adapter was redesigned where the oil filter is positioned 90 degrees offset adjacent to the starter motor — a Ford V8 oil filter can be used in place of the short filter increasing oiling capacity).

The first 4.0 L engines in 1987 had a Renix (Renault/ Bendix) engine management system considered quite advanced for their time. A knock sensor allowed the ECU to control spark advance in response to fuel octane and engine load. Unfortunately, few scan tools can interface with the system to pull diagnostics codes. RENIX systems also have no permanent memory for diagnostics codes, thus making diagnosing intermittent problems more difficult.

The 1987 Renix 4.0 L was rated at and . In 1988, the 4.0 received higher flowing fuel injectors, raising output to and — more power than some configurations of the Ford 302, Chevrolet 305, and Chrysler 318 V8 engines, and more than any of the Japanese 6-cylinder truck engines, but with comparable or superior fuel economy.

In 1991, a Chrysler multi-port fuel injection system replaced the RENIX system, and the intake ports were raised approximately for a better entry radius. Chrysler also enlarged the throttle body and redesigned the intake and exhaust manifolds for more efficiency, and the fuel injectors were replaced with higher flow units. The camshaft timing was also changed. The net result was an engine that made and . Badging on most Jeeps equipped with this engine reads "4.0 Litre HIGH OUTPUT." The new cam profile combined with altered computer programming eliminated the need for an EGR valve and knock sensor, but made the engine more sensitive to alterations, especially where emissions are concerned. The OEM fuel injectors used with the Mopar MPI system (manufactured by Siemens) have been known to leak fuel especially with OBD-II where plugged catalytic converters are common which usually throws a P0420 code.

Minor changes were made to the cylinder head for the 1995 model year. In 1996, the engine block was redesigned for greater strength. The new block had more webbing and a stud girdle for added rigidity of the crankshaft main bearings. Engines installed in 1999 Grand Cherokees carried the " PowerTech" name that had been used intermittently in prior years and on other Chrysler truck and SUV engines. The name was subsequently passed on to 4.0s in the other Jeep models that used the engine, the Cherokee and Wrangler. The cylinder head was again changed for the 2000 model year to a more emissions-friendly design. This head was designated as "0331" in the casting number. Early 0331 heads are prone to cracking, causing coolant to contaminate the oil, which can lead to catastrophic engine failure. The head cracks in the center between #3 and #4 cylinders. The crack is usually discernible with the valve cover removed as a "milky" tan line. This condition is usually discovered before a catastrophic engine failure, but can lead there if not corrected promptly. The casting was fixed in mid to late 2001, but the same casting number was retained. The "fixed" heads have "TUPY" cast in the center where the cracks used to occur. Also new for the 2000 model year, was the distributor-less, coil on plug ignition system. Option code: ERH.

Output:
:* 1987–1990: at 4500 rpm and at 2500 rpm
:* 1991–1995: at 4750 rpm and at 4000 rpm
:* 1996–2001: at 4600 rpm and at 3000 rpm
:* 2001–2006: at 4600 rpm and at 3200 rpm

The 4.0 L engine was discontinued at the end of the 2006 model year, replaced in the redesigned 2007 JK Jeep Wrangler by Chrysler's 3.8 L OHV V6, which originated in the company's minivans.

*1987–2001 Jeep Cherokee
*1993–2004 Jeep Grand Cherokee
*1987–1990 Jeep Wagoneer
*1987–1992 Jeep Comanche
*1991–2006 Jeep Wrangler

Connecting rod lengths

1964–1970:
* —
* —
* —

1971–2006:
* —
* —
* —
* —
*The displacement differs between 1990–1995 and 1996–2006 versions of the 4.0 L engines by around . Both had a bore of , but the stroke decreased slightly from on the earlier engine to on 1996 and later engines. The small stroke change of was accomplished by moving the piston pin and changing the crankshaft stroke; the rod length did not change.

The deck height of the AMC six-cylinder block was increased by (half the rod length difference) in 1971 to allow for the longer stroke required for the 258. There are only two deck heights. Tall deck is . Short should be . Tall is from 1974 through 1976 AMC factory service manuals; before 1974, deck height was not printed. Deck height changed slightly over the years 1977–1982 service manuals state , the 1993 Jeep factory manual states . Deck heights may have changed to accommodate slightly different compression ratios over the years.

The 1971 and older blocks use a "small" bell housing bolt pattern exclusive to AMC and small Nash sixes. In 1972, the bell housing bolt pattern was changed to match the AMC V8s. Its final use was in 2006 when the 4.0 L was phased out. Four bolts on the cylinder block are matched to the transmission bell housing where an adapter plate serves as a dust cover — two additional bolt holes on the transmission bellhousing used on the AMC V8 are used to secure the dust cover. The 1971 model year 258 uses the "small" pattern, the only version of the 258 to do so.

See also

*AMC straight-4 engine
*AMC V8 engine
*List of AMC engines
* AMC and Jeep transmissions
* List of Chrysler engines

References

*

External links

AMC Rambler Club
encourages and promotes the preservation, restoration, and collection of automobiles produced by American Motors Corporation, as well as collecting information and printed matter relating to these cars

American Motors Owners Association
aiding and encouraging the use, enjoyment, preservation, and restoration of vehicles built by American Motors Corporation between 1954 and 1988 model years

{{American Motors

AMC engines
Chrysler engines
Straight-six engines
Jeep engines
Products introduced in 1964