AMC Jeep 4.2L L6 Remanufactured Engine – 1981-1985

Description

High-nickel cast iron block architecture absorbs extreme combustion pressure spikes while hypereutectic aluminum pistons resist thermal expansion during grueling commercial transport operations in the AMC Jeep 258 Lightweight Remanufactured Engine engineered for 1981 to 1985 Jeep CJ-7, Scrambler, and Wagoneer commercial fleet vehicles. This lightweight-crankshaft 12-valve OHV inline-six platform restores high fuel economy and dependable trail crawling.

Cast from high-nickel gray cast iron, this revised 258 block incorporates a lightweight 46-pound nodular iron crankshaft and seven main bearing bulkheads that halt bottom-end deflection. A micro-polished crankshaft turns within tri-metal bearings, linked to forged steel connecting rods and graphite-coated hypereutectic aluminum pistons. Decks receive an Ra 35 finish for composite gasket sealing over diamond plateau honed bores. Dry mass measures 440 lbs with a 5.0-quart capacity stamped steel oil pan.

Key Features of AMC Jeep 258 Lightweight

Rural utility fleet managers buy AMC Jeep 258 Lightweight remanufactured engine packages to keep four-wheel-drive service trucks and park haulers operating on schedule. Every remanufactured long block undergoes vacuum decay testing to guarantee total fluid circuit separation before crate departure.

• Lightweight nodular iron crankshaft reduces rotating mass to improve engine acceleration and fuel efficiency
• In-block hydraulic flat-tappet camshaft profiles maximize low-end pulling torque across slow crawl speeds
• 0.0012 to 0.0020 inch main bearing clearances maintain solid hydrodynamic lubrication film strength
• Cast iron cylinder heads feature induction-hardened exhaust valve seats for unleaded fuel durability
• High-flow internal gear-type oil pumps channel pressurized lubricant to overhead pushrods and rocker arms
• Induction-hardened valve seats prevent valve face recession during continuous commercial fleet operation
• Precision rotating package balancing protects AMC Jeep 258 Lightweight driveline parts from vibration

AMC 258 Lightweight Operational Limits

Operating lubricant pressure produces 15 to 20 PSI during warm idle and expands to 40 through 55 PSI at 2000 RPM cruising speeds. Thermostats regulate internal coolant fluid movement between 180°F and 195°F to stabilize combustion heat transfer. This 4.2-liter pushrod inline-six generates 115 horsepower at 3200 RPM and 210 lb-ft continuous torque at 1800 RPM with a 9.2:1 compression ratio. Cylinder cranking pressure measures between 145 and 160 PSI across all six chambers. The cooling system rejects 2550 BTU per minute during uphill pulling.

AMC 258 Lightweight Crankshaft Alignment

A round 6-bolt rear crankshaft flange mounts flush to factory manual transmission flywheels or TorqueFlite automatic driveplates. Measured crankshaft thrust endplay checks out between 0.0030 and 0.0070 inches. The 1.250-inch front crankshaft snout features a single keyway to position the timing crank gear and harmonic balancer, holding true accessory drive serpentine belt pulley alignment.

AMC 258 Lightweight Fleet Protocols

Technicians must prime the internal oil passages using an external priming tool inserted through the distributor hole before initial startup. Use high-zinc 10W-30 mineral motor oil during initial cam break-in to protect flat-tappet lifters. This cast iron engine is not engineered for turbocharging, nitrous injection, or competitive rock-bouncing.

• Check crankcase oil level and coolant tank fluid volume each shift before vehicle dispatch
• Drain break-in motor oil and install fresh oil filter after 500 initial road miles
• Perform routine oil and filter changes every 3000 miles during commercial transit cycles

AMC 258 Lightweight Warranty Details

Commercial fleet purchasers receive a 3-Year / 100,000-Mile commercial fleet warranty covering structural casting and internal moving components. The heavy-duty wood crate contains one remanufactured long block engine, a complete engine install gasket set, spark plug well seals, front timing cover seals, dyno test documentation, and priming instructions.