The AMC straight-6 engine is a family of straight-six engines that were produced by American Motors Corporation (AMC), and used in AMC passenger cars and Jeep vehicles from 1964 through 2006. Production continued after Chrysler acquired AMC in 1987.
AMC Straight-6 engine | |
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Overview | |
Manufacturer | American Motors Corporation |
Production | 1952–2006 |
Layout | |
Configuration | Naturally aspirated Straight-6 |
Displacement | 195.6 cu in (3.2 L) 199 cu in (3.3 L) 232 cu in (3.8 L) 242 cu in (4.0 L) 252 cu in (4.1 L) 258 cu in (4.2 L) 282 cu in (4.6 L) |
Cylinder bore | 3+3⁄4 in (95.3 mm) 3.875 in (98.4 mm) 3.91 in (99.3 mm) 3.917 in (99.5 mm) |
Piston stroke | 3 in (76.2 mm) 3.414 in (86.7 mm) 3.4375 in (87.31 mm) 3+1⁄2 in (88.9 mm) 3.895 in (98.9 mm) |
Cylinder block material | Cast-iron head = Cast-iron valvetrain = OHV 2 valves x cyl. |
Compression ratio | 7.7:1, 8.0:1, 8.5:1, 9.5:1 |
Combustion | |
Fuel system | Carburetor Multi-port fuel injection |
Management | AMC CEC Renix or Mopar (manufactured by Siemens) |
Fuel type | Gasoline |
Cooling system | Water-cooled |
Output | |
Power output | 129–200 hp (96–149 kW; 131–203 PS) |
Torque output | 216–280 lb⋅ft (293–380 N⋅m) |
Dimensions | |
Dry weight | 483 lb (219 kg) (4.0 L engine) |
The initial I6 engine design was a legacy model initially designed by Nash Motors and was discontinued in 1964.
A completely new design was introduced by AMC in 1964. The engine evolved in several displacements and underwent upgrades. This family of I6 engines was also manufactured by Vehículos Automotores Mexicanos and included 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.
American Motors' first straight-six engine was the 196 cubic inch (195.6 cu in (3.2 L)) produced from 1952 through 1965, initially as a flathead (L-head) side-valve, and later an overhead valve (OHV) version.
The 196 was originally designed to be an economy engine by Nash Motors, the company that merged with Hudson to form AMC in 1954.[1] This engine was introduced in the 1941 Nash Ambassador 600 model.[2][3] The intake and exhaust manifolds were integrated into the cylinder block casting to reduce both weight and cost.[2] It had four main bearings, unlike the 7-main-bearing 234 flathead engine it replaced. The new flathead design had a smaller displacement, 172.6 cu in (2.8 L) and was initially rated at 75 hp (56 kW; 76 PS).[2] The engine combined with the new Ambassador's advanced "unitized" construction design provided better than 25 mpg‑US (9.4 L/100 km; 30 mpg‑imp).[4] Using the same 3.125 in (79.4 mm) bore, this engine was enlarged in 1950 to 184 cu in (3.0 L) for the Nash Statesman, and ultimately to 195.6 cu in (3.2 L) by using different strokes, an unusual practice given that changing forging is more expensive than changing the block casting.[5]
This engine was redesigned as an OHV for the 1956 model year.[5] The flathead version was discontinued between 1956 and 1957, but reemerged in 1958 as the economy engine for the "new" Rambler American and was available through 1965.[5] The new OHV configuration for 1956 continued with the water pump mounted on the left side of the engine (driven by a shaft extending from the back of the generator).[5] This was changed for 1957 with the water pump mounted on the front of the engine above the timing chain.[5] When the flathead model was reintroduced, it received a new water pump. Featuring high-quality parts such as forged crankshafts and connecting rods, these engines earned a reputation for durability. However, the flathead was prone to the typical problem of overheating under sustained heavy loads. The excessive heating was caused by the hot exhaust going through the cylinder block to the exhaust manifold.
American Motors introduced a die-cast aluminum block version of the OHV 195.6 cu in (3.2 L) engine in 1961. It was produced through 1964.[6] This engine used cast-iron cylinder liners and a cast-iron head. The cylinder heads for the two types of block (aluminum and cast iron) have similar designs but are not interchangeable. The cylinder head for the aluminum block is roughly 1/8" wider than that for the cast-iron block and uses a slightly different head bolt pattern.[7]
The 196 OHV requires more periodic maintenance than newer-model engines. The head bolts must be re-torqued (retightening process) regularly.[8] 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). Modern head gaskets can extend this service interval to re-torque the bolts every 12,000 mi (19,000 km), or every other year. The cause of the head bolts loosening over time is believed to be thermal expansion and contraction of the head due to the rather heavy design. The head expands and contracts by as much as 0.02 in (0.51 mm) in height during normal operation; this loosens the bolts over time and eventually will cause the seal between the head and block to fail.[9] This maintenance is also imperative to prevent the engine from overheating (the first sign of a blown head gasket) and 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 allowed to overheat. Good replacement heads and aluminum blocks for these engines are now difficult to find.[10]
American Motors designed a new six-cylinder with a short stroke and seven main bearing crankshaft that was introduced in 1964. This engine design was produced by AMC and VAM in various forms as well as Chrysler through 2006.
The 232 cu in (3.8 L) inline six was AMC's first modern six-cylinder engine.[11] Road tests by Consumer Reports described the new powerplant as "a very smooth and quiet engine, which should give good performance."[12]
To commemorate the engine's May 1964 launch, a total of 2,520 "Typhoon" versions were made based on the Rambler Classic hardtop body.[13] The two-door hardtops featured the 145 hp (108 kW; 147 PS) 8.5:1 compression ratio engine, Solar Yellow body paint, a Classic Black roof paint, and a distinctive "Typhoon" script in place of the usual "Classic" name. All other AMC options (except engine options) were available.[14]
For the 1965 model year, the new 232 engine replaced the Nash 195.6 cu in (3.2 L) OHV I6 in the Classic and Ambassador models. This was also the first availability of a six in the Ambassador line since 1956.
In 1966, a 199 cu in (3.3 L) version of the 232 replaced the OHV and L-head 195.6 cu in (3.2 L) engines in AMC cars.
Both the 199 and 232 featured a 3+3⁄4 in (95.3 mm) bore, and either a 3 in (76.2 mm) or 3+1⁄2 in (88.9 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.
The 199 cu in (3.3 L) engine was produced from 1965 through 1970.
The 199 AMC engine was selected by Barney Navarro to power a race car for the Indianapolis 500. Navarro applied turbocharging to a variety of engines that led to the Indy-related application "based on a Stone-Age-strong Nash 6."[15]
This engine had never before used in an IndyCar, but Navarro selected it "due both to its strong bottom end and thick cylinder walls."[16] For the first Indy attempt, Navarro designed fuel-injection system and a single turbo for the engine that produced 550 hp (410 kW; 558 PS) at 6000 rpm. This was a dead-stock block with seven main bearings and large journal sizes to which Navarro modified the head while the second block was drilled for four-bolt caps.[17] Successive engines incorporated double turbochargers to produce 640–700 hp (477–522 kW; 649–710 PS).[18][19]
Navarro fielded a 1964 Watson car with the AMC 199 engine for three years at the Indianapolis 500 race.[20] However, the #50 Navarro-Rambler never qualified due to problems with drivers and with the suspensions of the cars.[16][21] The car was entered at the 28 February 1971 IndyCar "Rafaela 300" season opener in Argentina. This was its fourth actual race start at 19 on the starting grid and driven by Dave Strickland for 45 laps.[22] This car was then driven by Les Scott in practice for 1971 Indy 500 race.[23] The next year, another attempt to qualify was with Leon Sirois as the driver.[23]
On 14 July 2005, the remaining contents of Navarro Engineering in Los Angeles were auctioned.[24] The Navarro's 700 hp (522 kW; 710 PS) 199 cu in (3.3 L) engine was purchased by a private collector for $15,000.[24]
The 232 cu in (3.8 L) 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.[25]
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.[26] 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.[26]
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 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.[26]
Changes for the 1976 model year included fuel economy improvements that reduced emissions and warmup time.[27] 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.[27]
The 252 cu in (4.1 L) 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 3.91 in (99.3 mm) bore, for an actual displacement of 252.15 cu in (4.1 L). It was produced in VAM's Lerma, Estado de México engine plant.
Output for 1972 Rambler American Rally model (gross):
Engine dimensions:
The 258 cu in (4.2 L) was produced from 1971 through 1990. It featured an undersquare 3.75 in (95.3 mm) bore and 3.895 in (98.9 mm) 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 97mm 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.[29] 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 20 pounds (9.1 kg).
This engine also found use in farm/industrial applications such as the International Harvester 4000 swather.
The 282 cu in (4.6 L) 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 3.917 in (99.5 mm) bore, 0.16 in (4.1 mm) larger than the 258, making 281.7 cu in (4.6 L).[30] 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):
Output for 1974 models (gross):
Output for 1975–1976 models (gross):
Output for 1977–1978 models (gross):
Output for 1979–1981 Standard models (net):
Output for 1979 American 06/S and 1980–81 Rally GT models (net):
Output for 1982–1983 models (net):
Engine dimensions:
The 242 cu in (4.0 L) engine was developed by AMC in just 26 months using many off-the-shelf components while featuring, among others, additional strength, improved combustion chamber, port setup, and cam profile.[31] The total weight of the new engine was 483 pounds (219 kg), only one pound more than the 258 six despite its heavier components and parts.[31] The cast aluminum valve cover featured 15 bolts, the industry's most, to achieve a positive seal.[31]
The new engine, which was introduced in 1986 for the 1987 model year, was a further evolution of AMC's 258 six.[32][33] It had a 3.875 in (98.4 mm) bore and a 3.414 in (86.7 mm) stroke giving it a displacement of 241.6 cu in (4.0 L).[34] 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.[35] 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.[36] 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."[37] The engine is known for longevity, and can sometimes go more than 300,000 miles (482,803 km) without rebuilding.[38][39] 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."[40]
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 20 mm (0.79 in) 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.[29] 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.[41]
The 1987 Renix 4.0 L was rated at 173 hp (129 kW; 175 PS) and 220 lb⋅ft (298 N⋅m). In 1988, the 4.0 received higher flowing fuel injectors, raising output to 177 hp (132 kW; 179 PS) and 224 lb⋅ft (304 N⋅m) — 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.[41]
In 1991, a Chrysler multi-port fuel injection system replaced the RENIX system, and the intake ports were raised approximately 1⁄8 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 replaced with higher flow units. The camshaft timing was also changed. The net result was an engine that made 190 hp (142 kW; 193 PS) and 225 lb⋅ft (305 N⋅m). 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.[citation needed] 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.[citation needed] 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.[42] Also new for the 2000 model year, was the distributor-less, coil on plug ignition system.[43] Option code: ERH.
Output:[44]
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.
1964–1970:
1971–2006:
The deck height of the AMC six-cylinder block was increased by 1⁄8 in (3.2 mm) (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 9.528–9.534 in (242.0–242.2 mm). Short should be 9.278–9.284 in (235.7–235.8 mm). 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 9.487–9.493 in (241.0–241.1 mm), the 1993 Jeep factory manual states 9.429–9.435 in (239.5–239.6 mm). Deck heights may have changed to accommodate slightly different compression ratios over the years.[45]
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.
bore x stroke = 3.875 x 3.414 inches