In 1987 AMC introduced the 4.0-liter six-cylinder engine into its Jeep vehicles. The engine was designed to replace the 4.2-liter six-cylinder engine. The 4.0-liter engine is found in AMC's, and later Chrysler's, Jeep Cherokee, Wrangler and Wagoneer. The oldest of these engines are reaching 24 years of age, so home mechanics may need to overhaul them to extend their service life. Many companies provide aftermarket parts for Jeeps that use this engine.
Remove the valve cover. Using the socket wrench, remove the valve cover to expose the valve train.
Remove the rocker arm bolts. Using the socket wrench, remove the bolts and remove the rocker arms and pivots from the cylinder head studs. Label and store each rocker arm, pivots and bolts separately. They must be re-installed in their original locations.
Remove the lifters. Use the spring compressor to compress a spring enough to use the needle nose pliers to remove the spring keeper. Slowly release the pressure on the spring and remove the retainer, spring and spring seat. Keep the lifter set from each cylinder and valve labeled and stored separately.
Remove the valves. Pull each valve from the cylinder head and remove the oil seal from the guide. Inspect the valves, valve stems and rocker arm tips for wear. Use the digital caliper to check the lifter springs for sagging. Use the Jeep's service manual for the correct spring length specification.
