The AMC straight-6 engine is a family of inline 6-cylinder engines that were produced by American Motors Corporation and used in AMC passenger cars and Jeep vehicles from 1964 through 2006. Production continued by Chrysler after it acquired the American Motors Corporation in 1987.
The initial I6 engine design was a legacy model originally 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 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.
196
American Motors' first straight-six engine was the 196 cubic inch () 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. This engine was introduced in the 1941 Nash Ambassador 600 model. The intake and exhaust manifolds were integrated into the cylinder block casting to reduce both weight and cost. It had four main bearings, unlike the 7-main-bearing 234 flathead engine it replaced. The new flathead design had a smaller displacement, and was initially rated at . The engine combined with the new Ambassador's advanced "unitized" construction design provided better than . Using the same bore, this engine was enlarged 1950 to for the Nash Statesman, and finally to by using different strokes, an unusual practice given that changing forging is more expensive than changing the block casting.
This engine was redesigned as an OHV for the 1956 model year. The flathead version was discontinued during 1956 and 1957, but reemerged in 1958 as the economy engine for the "new" Rambler American and was available through 1965. 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). This was changed for 1957 with the water pump mounted on the front of the engine above the timing chain. When the flathead model was reintroduced it also received a new water pump. Featuring high-quality parts such as forged crankshafts and connecting rods, these engines earned a reputation for 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 Motors introduced a die-cast aluminum block version of the OHV engine in 1961. It was produced through 1964. 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) are of similar design, 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.
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 and to re-torque them every . With modern head gaskets this service interval can be extended to re-torque the bolts every , or every other year. The cause of the headbolts 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 in height during normal operation, this loosens the bolts over time and eventually will cause the seal between the head and block to fail. 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.
232
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 inline six was AMC's first modern six-cylinder engine.