AMC Straight-6 engine

The American Motors Corporation (AMC) straight-6 family of engines was used by a number of AMC and Jeep vehicles from 1964 through 2006.

195.6
American Motors' first straight-six engine was the 195.6 cu in (3.2 L). It was produced from 1958 through 1965 in both overhead valve (OHV) and flathead (L-head) side-valve versions.

Sometimes referred to as the 196 engine, this engine was originally designed by Nash in the 1930s as a flathead, and redesigned as an OHV engine in 1956. The flathead version was discontinued for 1956–1957, but reemerged in 1958 as the economy engine for the "new" Rambler American. When the engine was changed to an OHV configuration the water pump was moved from the left side of the engine (driven by a shaft extending from the back of the generator) to the front above the timing chain. When the flathead model was reintroduced it also received the new water pump. Equipped with such high quality parts as forged crankshafts and connecting rods, these engines earned a reputation for remarkable durability. The flathead, however, was prone to the typical flathead problem of overheating under sustained heavy load. This was from the hot exhaust traveling through the cylinder block to the exhaust manifold.

American Motor introduced an aluminum block version of the OHV 195.6 cu in (3.2 L) engine in 1961. It was produced through 1964. This engine used cast iron cylinder liners and a cast iron head. The head is slightly wider on the right side than the cast iron block head. The heads will physically interchange, but the head designed for the cast iron block will need material added to its right side to properly seal on an aluminum block.

The 196 OHV requires more periodic maintenance than newer model engines. The head bolts must be re-torqued (retightening process) regularly. Factory service manuals recommend that head bolt torque be checked every 4,000 mi (6,400 km) and to re-torque them every 8,000 mi (13,000 km). With modern head gaskets this service interval can be extended to re-torque the bolts every 12,000 mi (19,000 km), or every other year. The exact cause of the headbolts loosening over time is unknown, but it is believed that thermal expansion and contraction of the block, head, and bolts eventually causes the seal between the head and block to loosen. This maintenance is imperative to prevent the engine from running hot (the first sign of a blown head gasket) and thus warping or cracking the head. The cast iron liners in the aluminum block version can also shift if the head bolts are not properly torqued and the engine is run hot. If this process is not followed, then repairs will be necessary and replacement heads and aluminum blocks for these engines are now more difficult to find

The modern era I-6
The company designed an entirely new six-cylinder with a short stroke and seven main bearing crankshaft for 1964. This design was produced in various forms through 2006. The 232 cu in (3.8 L) "Torque Command" inline six was AMC's first modern six cylinder engine.[1]

To commemorate the engine's May 1964 introduction, 2,520 "Typhoon" cars were made on the Rambler Classic hardtop body.[2] Each featured the 145 hp (108 kW) 8.5:1 compression ratio engine, Solar Yellow body paint, a Classic Black roof, and a distinctive "Typhoon" script in place of the usual "Classic" name. All other AMC options (except engine options) were available.[3]

The new engine replaced the Nash 195.6 cu in (3.2 L) OHV I6 in the Classic and Ambassador for the 1965 model year (this was also the first use of a six in the Ambassador since 1956).

In 1966, a 199 cu in (3.3 L) version finally replaced the aging 195.6 cu in (3.2 L) OHV and L-head engines. Road tests by Consumer Reports described the new powerplant as "a very smooth and quiet engine, which should give good performance."[4]

Both the 199 and 232 featured a 3.75 in (95 mm) bore, and either a 3.0 in (76 mm) or 3.5 in (89 mm) stroke. The 199 was discontinued in 1970; the 232 was offered alongside the 258 cu in (4.2 L) (made by using a 3.895 in (98.9 mm) stroke crankshaft and slightly taller block) during the 1970s, but was discontinued in 1979. Increasingly stringent emission control regulations continued to decrease the engine's power output, making the smaller version inadequate as increasingly stringent safety regulations also made vehicles heavier.

199
The 199 cu in (198.8 cuin / 3,258 cc) 199 was produced from 1965-1970.

Applications:
 * Rambler Classic (1965–66, fleet cars only)
 * Rambler American/AMC Rambler (1965–69)
 * AMC Hornet (1970)
 * AMC Gremlin (1970)

232
The 232 cu in (3.8 L) (231.9 cu in / 3,801 cc) 232 was produced from 1964 to 1979. The 232 was the base six-cylinder engine on many models through 1979, and even towards the end of its usage was considered reasonably modern in design.[5]

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 1971-1975 Jeep CJ-5.[6] Air conditioning was available only with the older 196 engine in the American, because there wasn't space for it with the longer 232.[6]

Through the 1970 model year, the 232 shared a deck height with the 199 cu in (3.3 L) engines. Starting in 1971, AMC raised the deck height to produce the 258, and the 232 adopted the 199's longer connecting rods. Bore and stroke remained the same.

In 1972, the bell housing bolt pattern changed to match the larger version used on the V8 engines.[6]

Changes for the 1976 model year included fuel economy improvements that also reduced emissions and reduced warmup time.[7] This was accomplished by reshaped carburetor air passages that pushed the fuel efficiency of a 232-equipped AMC Gremlin to 30 mpg-US (7.8 L/100 km; 36 mpg-imp) as tested by the United States Environmental Protection Agency, compared to 24 mpg-US (9.8 L/100 km; 29 mpg-imp) in 1975.[7]

Applications:
 * Rambler Classic (1964–1966)
 * Rambler American/AMC Rambler (1964–1969)
 * Rambler/AMC Marlin (1965–1967)
 * Rambler/AMC Ambassador (1965–1970)
 * Rambler/AMC Rebel (1967–70)
 * AMC Javelin (1968–74)
 * AMC Hornet (1970–77)
 * AMC Gremlin (1970–78)
 * AMC Matador (1971–74)
 * AMC Pacer (1975–79)
 * AMC Concord (1978–79)
 * AMC Spirit (1979)
 * Jeep CJ (1972–79)
 * Jeep Cherokee (1974–79)
 * Jeep Wagoneer (1965–1971)
 * Jeep J series trucks (1965–1970)
 * Jeep Commando (1972–1973) (1976 in Spain)
 * International Harvester Scout (1969–1971)

252
The 252 cu in (4.1 L) engine was produced by AMC's Mexican subsidiary Vehiculos Automotores Mexicanos (VAM) beginning in 1969 and was dropped in 1972, replaced with AMC's 258 for the 1973 model year and later models. This was similar to a 232 in stroke with a larger 3.91 in (99 mm) bore, for an actual displacement of 252.15 cu in (4,132.0 cc). Output for 1972 Rambler American Rally model:
 * Horsepower 170 hp @ 4600 rpm
 * Torque 240 lb-ft @ 2300 rpm

Engine dimensions:
 * Compression ratio 9.5:1 (standard model was 8.5:1)
 * Intake valve diameter 2.020 in
 * Exhaust valve diameter 1.6755 in
 * Pushrod length 5.875 in
 * Deck height 9,424 in
 * Bore 3.910 in
 * Stroke 3.50 in

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

258
The 258 cu in (4.2 L) was produced from 1971-1990. It featured an undersquare 3.75 in (95 mm) bore and 3.895 in (98.9 mm) stroke; it was otherwise similar to the 199 and 232. This engine is considered reliable, inexpensive, and torquey."[9] 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. Applications:
 * AMC Hornet/Concord/Spirit/Eagle (1971–1988)
 * AMC Pacer (1975–1980)
 * AMC Matador (1971–1978)
 * AMC Gremlin and Spirit (1971–1983)
 * International Harvester Scout and Light Duty trucks (1972–1974)
 * Jeep CJ (1972–1986)
 * Jeep Cherokee and Wagoneer (1972–1986)
 * Jeep J series trucks (1971–1988)
 * Jeep Wrangler (1987–1990)
 * Jeep Commando (1972–1973)

282
The 282 cu in (4.6 L) engine was produced by AMC's Mexican subsidiary Vehiculos Automotores Mexicanos (VAM) beginning in 1971 through 1986. This was similar to a 258 in stroke, cast with a larger 3.917 in (99.5 mm) bore, 0.16" larger than the 258, giving 281.7 cu in (4,616 cc).[10]

Output for 1977-78 models (gross):
 * Horsepower 200 hp @ 4400 rpm
 * Torque 280 lb-ft @ 2200 rpm
 * Compression ratio 8:1

Output for 1979-81 Standard models (net):
 * Horsepower 132 lb @ 3800 rpm
 * Torque 216 lb-ft @ 2200 rpm
 * Compression ratio 8:1

Output for 1979 American 06-S and 1980-81 Rally GT models (net):
 * Horsepower 172 hp @ 4200 rpm
 * Torque 225 lb-ft @ 2600 rpm
 * Compression ratio 8.5:1

Output for 1982-83 models (net):
 * Horsepower 129 hp @ 4000 rpm
 * Torque 218 lb-ft @ 1800 rpm
 * Compression ratio 8.5:1

Engine dimensions:
 * Intake valve diameter 2.020 in
 * Exhaust valve diameter 1.6755 in
 * Pushrod length 5.875 in
 * Deck height 9.424 in
 * Bore 3.917 in
 * Stroke 3.895 in

Applications:
 * VAM Pacer and Pacer X (U.S. equivalent - AMC Pacer base and X coupe)
 * VAM Rally AMX, Rally SST, and Rally GT (U.S. equivalent - AMC Spirit GT and Limited coupe)
 * VAM American GFS, American ECD, American DL, and American Rally (U.S. equivalent - AMC Hornet D/L and X plus AMC Concord D/L and Limited)
 * VAM American Rally AMX (U.S. equivalent - AMC Concord AMX hatchback)
 * VAM Classic AMX and Classic Brougham (U.S. equivalent - AMC Matador X and Brougham coupe plus 1972 AMC Matador hardtop)
 * VAM Classic DPL (U.S. equivalent - AMC Matador Sedan)
 * VAM Javelin from 1971 through 1973 (U.S. equivalent - AMC Javelin)
 * VAM Lerma

4.0
The 242 cu in (4 L) engine introduced in 1987 was an evolution of the 258.[11] It had the same 3.895 in (98.9 mm) bore as the 2.5 with a longer 3.414 in (86.7 mm) stroke giving it a displacement of 241.6 cu in (3,959 cc).[12]

The 4.0 is one of AMC's best-known engines.[13] 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 is regarded as one of the best 4x4 off-road engines,[14] and it is known to be able to go more than 300,000 miles (480,000 km) without rebuilding.[15] There are many aftermarket parts available.[citation needed]

The first 4.0 engines in 1987 had a RENIX (Renault/Bendix) engine management system considered quite advanced for their time.[9] A knock sensor allowed the ECU to control spark advance in response to fuel octane and engine load. Unfortunately, there are few scan tools capable of interfacing with the system to pull diagnostics codes. RENIX systems also have no permanent memory for diagnostics codes thus making the diagnosis of intermittent problems more difficult.[16]

The 1987 RENIX 4.0 made 173 hp (129 kW) and 220 lb·ft (300 N·m). In 1988, the 4.0 received higher flowing fuel injectors, raising output to 177 hp (132 kW) and 224 lb·ft (304 N·m)—more power than some configurations of the Ford 302, Chevrolet 305, and Chrysler 318 8-cylinder engines, and more than any of the Japanese 6-cylinder truck engines, but with comparable or superior fuel economy.[17]

In 1991, Chrysler redesigned the RENIX engine control computer and raised the intake ports approximately .125 in (3.2 mm) 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 once again replaced with higher flowing units. The camshaft profile was also changed. The net result was an engine that made 190 hp (140 kW) and 225 lb·ft (305 N·m). Badging on most Jeeps equipped with this engine read "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.[citation needed]

Small 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, which had been used intermittently in prior years and on other Chrysler truck and SUV engines[which?]. 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 lower flowing, more emissions-friendly design.[citation needed] This head was designated as "0331" in the casting number. These heads are prone to cracking and causing coolant to contaminate the oil, resulting in catastrophic engine failure.[citation needed] Also new for the 2000 model year, was the distributorless, coil on plug ignition system.[citation needed]

Output as of 2004 was 190 hp (142 kW) at 4600 rpm with 230 lb·ft (310 N·m) at 3000 rpm.

The 4.0 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. The 4.0 engine was also made in China, where a slightly modified version of the XJ Jeep Cherokee with 2.5 and 4.0 engines were produced alongside the Chinese-produced WJ Grand Cherokee since 2006.

This engine was used in the following vehicles:
 * 1987–2001 Jeep Cherokee
 * 1993–2004 Jeep Grand Cherokee
 * 1987–1990 Jeep Wagoneer
 * 1987–1992 Jeep Comanche
 * 1991–2006 Jeep Wrangler

Connecting Rod lengths
1964-71:
 * 199 CID (3.3 L) - 6.125 im
 * 232 CID (3.8 L) - 5.875 in

1972-2006:
 * 232 CID (3.8 L) - 6.125 in
 * 242 CID (4.0 L) - 6.125 in
 * 258 CID (4.2 L) - 5.875 in

The displacement differs between 1990–1995 and 1996-2006 engines by 2 cubic inches. Both had a bore of 3.88 in (99 mm), while the stroke decreased slightly from 3.44 inches (87.38 mm) on the earlier engine to 3.41 inches (86.61 mm) on 1996 and later engines. The displacement of both engines still rounds to 4.0 litres (3999.83 cc v. 3964.95 cc).