AMC Straight-6 engine

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

  • For an outline of all engines used by AMC see
Main article: AMC Engines

Contents

[edit] 195.6

AMC's first straight-6 was the 195.6 in³ (3.2 L). It was produced from 1958 through 1965 in both overhead valve (OHV) and "flathead" 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 and 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, from the hot exhaust traveling through the cylinder block to the exhaust manifold.

AMC introduced an aluminum block version of the OHV 195.6 in³ (3.2 L) engine in 1961. It was produced through 1964. This engine used cast iron cylinder liners and a cast iron head.

[edit] The modern era I-6

Engine bay of a 1968 Rambler American
Engine bay of a 1968 Rambler American

The company designed an entirely new six cylinder for 1964, and was produced, albeit in a modified form, up until 2006.

First produced in 1964 and introduced as an option in the Classic and Ambassador in the middle of the 1964 model year, the 232 in³ (3.8 L) "Typhoon" inline-6 was AMC's first modern 6-cylinder engine. It replaced the Nash 196 in³ (3.2 L) OHV I-6 in the Classic and Ambassador in 1965 (the first use of a six in the Ambassador since 1956). In 1966 a 199 in³ (3.3 L) version finally replaced the aging 196 in³ (3.2 L) OHV and L-head engines. To commemorate the engine's May 1964 introduction, 2,520 "Typhoon" cars were made on the Classic hardtop body. Each featured the new 232 six, 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.

Both the 199 and 232 featured a 3.75 in (95 mm) bore, and either a 3.0 in (76.2 mm) or 3.5 in (88.9 mm) stroke. The 199 was discontinued in 1970; the 232 was offered alongside the 258 (made by using a 3.9 in (99 mm) stroke crankshaft in the existing block) during the 1970s, but was discontinued in 1979. Increasing emissions controls continued to rob the engine of power, making the smaller version inadequate as safety regulations also added weight to the vehicles it was required to push around.

AMC changed the deck height of the six in 71, increasing it 1/8″ to make the 258. This alters pushrod length on all engines built after 71, and 71 model year engines may be of either deck height.

[edit] 199

The 199 in³ (3.3 L) 199 was produced from 1965 through 1970.

Applications:

[edit] 232

The 232 in³ (3.8 L) 232 was produced from 1964 through 1979.

Applications:

[edit] 258

Engine bay of a 1980 AMC Spirit AMX with numerous emissions controls
Engine bay of a 1980 AMC Spirit AMX with numerous emissions controls

The 258 in³ (4.2 L) inline-6 was produced from 1971 until 1990. It featured an undersquare 3.75 in (95 mm) bore and 3.90 in (99 mm) stroke; it was otherwise identical to the 199 and 232. Later 258 models (starting with the 1980 model year for California AMCs, 1981 for California Jeeps and 1982 for all other applications) are equipped with AMC's CEC system.

Applications:

[edit] 4.0

Engine bay of a 1993 Jeep Grand Cherokee with 4.0 L
Engine bay of a 1993 Jeep Grand Cherokee with 4.0 L

The 4.0 L (242 in³; 3956 cc) straight-6 was an evolution of the 258 and 2.5 and appeared in 1987. It had the same 3.88 in (98.4 mm) bore as the 2.5 with a longer 3.41 in (86.7 mm) stroke. The 4.0 was discontinued at the end of the 2006 model year as the redesigned Jeep Wrangler uses Chrysler's 3.8 L OHV V6.

The first 4.0 engines in 1987 had RENIX (Renault/Bendix) engine control systems, which were quite advanced for their time, but are now handicapped because there are very few scan tools which can be "plugged in" to a RENIX system for diagnosis. The Renix also used a very advanced engine knocking sensor, which allowed the computer to know if detonation was occurring, thus allowing the computer to make the appropriate changes to prevent this.

The 1987 RENIX 4.0 made 173 hp (129 kW) and 220 lb-ft (298 N·m) of torque. In 1988 the 4.0 received higher flowing fuel injectors, taking output to 177 hp (132 kW) and 224 lb-ft (304 N·m) respectively.

In 1991 Chrysler Corporation, then the owners of the Jeep brand, redesigned the RENIX engine control computer and raised the intake ports approximately 1/8″ 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 of all these changes was an engine that made 190 hp (142 kW) and 225 lb-ft (305 N·m) of torque. Badging on 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 make the engine more sensitive to alterations, especially where emissions are concerned.

Small changes were made to the cylinder head for the 1995 model year. In 1996, the engine block was redesigned, and a new strengthened unit was then used. The new block made use of more webbing cast into the block, and a stud girdle for added rigidity of the crankshaft main bearings. The cylinder head was also again changed around 1998 to a lower flowing, but more emissions friendly, design. Engines installed in 1999 Grand Cherokees carried the Power Tech name, which was subsequently passed on to 4.0s in all Jeep models.

The 4.0 engine was in production in North America until 2006, when the Jeep Wrangler TJ was replaced by the new JK design that uses Chrysler's OHV 3.8 L V6. It is foreseeable that this engine may be made for many more years in the People's Republic of China, where a slightly modified version of the XJ Jeep Cherokee with 2.5 and 4.0 engines are still being produced.

Output as of 2004 was 190 hp (142 kW) at 4600 rpm with 230 lb-ft (312 N·m) of torque at 3000 rpm.

This engine is considered one of the best offroad engines ever made. The extreme low end torque is ideal for trailing and rock crawling. The only downfall to the engine is the low power output for mudding applications but this can be fixed with various aftermarket options including a supercharger for the engine. Interchangeability within the late AMC/Jeep engine family is superb. The better flowing 4.0 L heads can easily be modified to fit earlier engines right along with the fuel injection system. The longer stroke 258 crankshaft and rods will drop right in the slightly larger bore 4.0 L block, easily creating an even higher torque 4.5 L engine with the stock bore (4.6 L bored 0.030″ over, and 4.7 L with a 0.060″ overbore). Blocks should be sonic checked for adequate cylinder wall thickness before boring 0.060″ over.

This engine was used in the following vehicles:

[edit] Rod Lengths

1964-71:

  • 199 (3.3L) - 6.125"
  • 232 (3.8L) - 5.875"

1972-06:

  • 232 (3.8L) - 6.125"
  • 242 (4.0L) - 6.125"
  • 258 (4.2L) - 5.875"

[edit] See also


American Motors Corporation
1954-1987

Historic:
Rambler: Ambassador by Rambler | American | Classic | Marlin | Rambler Six | Rambler Rebel
AMC: Ambassador | AMX | Concord | Eagle | Gremlin | Hornet | Javelin | Marlin | Matador | Mighty Mite | Metropolitan | Pacer | Rebel | Spirit
Renault: LeCar | Alliance | Encore | Fuego | Medallion | Premier
AMC & Rambler Concept Cars: Rambler Tarpon | AMC Cavalier | AMC AMX-GT | Amitron | Electron
Affiliated with: American Motors Corporation | AM General | Chrysler | Hudson | Jeep | Kelvinator | Nash Motors | Nash-Kelvinator | Rambler | Renault | Australian Motor Industries | Vehiculos Automotores Mexicanos
People Roy Abernethy | A.E. Barit | Roy D. Chapin Jr. | George W. Romney | Richard A. Teague | George W. Mason | Gerald C. Meyers | Edmund E. Anderson | François Castaing | Robert B. Evans | Richard E. Cross
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