AMC Straight-6 engine

[Jimmyb]

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

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.

In compensation, this required maintenance is quite easy. Re-torquing the head and adjusting the valves typically takes under 45 minutes to complete, start to finish, and is done with only two open-end wrenches and a feeler gauge. Some skills are required, but it is not challenging, and adjusting the valves on a running engine (as is required) is today a rare pleasure.



Modern head gaskets usually come with a statement that "no re-torque or sealant is required". This "no re-torque" refers to the process when the early gaskets had to be retightened upon installation after the engine had been run for a short period at full operating temperature. This procedure was necessitated by the type of material used for the gaskets. This process was usually called "bedding in" the gasket. Today, all replacement 196 head gaskets are made of modern materials and do not need to be retightened after the initial installation. However, they still require re-torquing every 8,000–12,000 mi (13,000–19,000 km) or every other year as noted previously.
It is imperative to use a sealant on all 196 head gaskets. Long-term experience of owners of cars with the 196 engine is that the gaskets need an additional sealant regardless of the gasket manufacturers recommendation.

A brush-on shellac (such as "Indian Head" brand) or spray-on copper or aluminum sealer is all that is needed. Without the additional sealer, the head gasket will seep a small amount oil into the water jacket and down the sides of the engine. Nevertheless, there seems to be a small amount of seepage on the right side even with sealer that is normal for this engine. This is likely due to the number of head bolts (15 — four around each cylinder plus one extra) and just adequate sealing surfaces — at least .25 in (6.4 mm) wide in all areas, but not much more in most. On the L-head engines, the head also seals the intake tract on the right side of the engine.



The company designed an entirely new six-cylinder with a short-stroke and seven main bearing crankshaft for 1964. This design was produced, albeit in a modified form, up until 2006. The 232 cu in (3.8 L) "Torque Command" in-line 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. 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 1971, increasing it by 0.125 inches (3.2 mm) to allow the longer stroke of the 258. This alters pushrod length on all engines built after 1971. The 232 was continued on the taller deck block by using the previous crankshaft with the slightly longer 199 rod.