The AMC 4.2L engine was produced from 1971-1990 and is very similar to the rest of the lineup of AMC inline-6 cylinder engines. These engines are considered to be very reliable, cheap to make, and torquey. It is found in many AMC and Jeep vehicles throughout the years and also found it’s way into some farm vehicles.
The AMC Inline-6 engine dates back as far as 1952, but the more iconic design was developed and released in 1964. Since then, that 3.8L (232 cu in) inline six has been modified throughout the years until 2006, when development of the 4.0L Inline-6 engine came to an end in the Wrangler TJ.
The 4.2L was produced between 1971 and 1990. Just like the other engines in it’s lineup, it was considered reliable and inexpensive to repair. In 1981, the engine had some small changes including an aluminum intake manifold, plastic rocker arm cover, and the crankshaft was redesigned to only have four counterweights instead of twelve, reducing the weight.
This engine was used in a variety of vehicles throughout AMCs lineup – but here are some of the Jeeps you can find it in!
- 1972-1988 Jeep CJ
- 1972-1986 Jeep Cherokee SJ and Wagoneer
- 1971-1988 Jeep J-Series Truck
- 1987-1990 Jeep Wrangler
- 1972-1973 Jeep Commando
Oil Types and Capacities
| Viscosity | Above 32°F: 10W-30, 10W-40, 20W-40 Above 0°F: 10W-30, 10W-40 Below 0°F: 5W-30 |
| Capacity | 6 qts |
| Oil Filter | Mopar 33004195 WIX 51626 |
| Drain Plug Torque | 30ft-lbs |
| Years | HP | TQ |
|---|---|---|
| 1987-90 | 112hp @ 3200rpm | 210lb-ft @ 2000rpm |
| 1982-1986 | 115hp @ 3200rpm | 210lb-ft @ 1800rpm |
| 1979-1981 | 110hp @ 3500rpm | 195lb-ft @ 2000rpm |
| 1972-1978 | 110hp @ 3500rpm | 195lb-ft @ 2000rpm |
| 1971 | 150hp @ 3800rpm | 240lb-ft @ 1800rpm |
Common Problems
Lifter Tick
Lifter tick is a common issue on these engines. While essentially harmless, many people do not enjoy the sound of the top of the engine slightly ticking when running. Besides replacing rockers and lifters, the only solution I’ve seen to work is to use a zinc additive in your oil or switch to an oil type that includes higher levels of zinc. One of the most recommended oils to use in the 4.2L engine (and 2.5L & 4.0L for that matter) is the Shell Rotella Diesel Engine Oil. The oil works great in the engine and includes lots of Zinc. As a result, this engine oil usually reduces lifter tick.
Modification
The 4.2L engine is essentially a tractor engine, and wasn’t designed to be used for high horsepower or performance applications. This is further indicated by it’s low horsepower numbers, but high low-end torque. Typically, there is not much that can be modified on this engine to significantly increase performance.
This engine is used in another type of engine build though – the Stroker engine. Stroker engines are highly modified, high performance 4.0L engines. Typically, the modifications include using the crank or piston rods from the 4.2L engine.
To learn more about stroker engines, visit the stroker forums here.
