AMC Jeep 4.2L L6 Remanufactured Engine – 1975-1979

Description

Meet strict commercial utility fleet maintenance benchmarks with 460 lbs of precision-machined cast iron powertrain engineering that outputs dependable low-RPM pulling power and active thermal control throughout the AMC Jeep 258 Mid-Era Remanufactured Engine engineered for 1975 to 1979 Jeep CJ and Wagoneer commercial fleet vehicles. This 12-valve OHV inline-six platform restores high low-end crawl torque and dependable multi-shift service.

Cast from high-nickel gray cast iron, this mid-era 258 block incorporates seven main bearing bulkheads that halt crankshaft flexing under heavy low-RPM pulling loads. A precision-ground nodular iron crankshaft pairs with forged I-beam connecting rods and hypereutectic aluminum pistons with anti-friction skirt coatings. Decks receive an Ra 35 finish for composite head gasket sealing. Dry mass measures 455 lbs with a 5.0-quart capacity stamped steel oil pan.

Key Features of AMC Jeep 258 Mid-Era

Municipal fleet supervisors buy AMC Jeep 258 Mid-Era remanufactured engine packages to keep classic utility trucks and park service vehicles operating on schedule. Every remanufactured long block undergoes vacuum decay testing to guarantee total fluid circuit separation before crate departure.

• Cast iron cylinder heads feature induction-hardened exhaust valve seats for unleaded fuel durability
• In-block hydraulic flat-tappet camshaft profiles maximize low-end pulling torque across slow crawl speeds
• 0.0012 to 0.0022 inch main bearing clearances maintain solid hydrodynamic lubrication film strength
• Heavy-duty timing chain and sprocket sets synchronize camshaft rotation without timing jump risks
• 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 Mid-Era driveline parts from vibration

AMC 258 Mid-Era 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 110 horsepower at 3500 RPM and 195 lb-ft continuous torque at 2000 RPM with an 8.0:1 compression ratio. Cylinder cranking pressure measures between 140 and 155 PSI across all six chambers. The cooling system rejects 2500 BTU per minute during uphill pulling.

AMC 258 Mid-Era Crankshaft Alignment

A round 6-bolt rear crankshaft flange mounts flush to factory manual transmission flywheels or 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 V-belt pulley alignment.

AMC 258 Mid-Era 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 Mid-Era 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.