Jeep 4.0 Engines-OP: How to Rebuild and Modify (Workbench How-to)

Price: $39.95 - $33.33
(as of May 06, 2025 19:49:52 UTC – Details)

The venerable Jeep 4.0L in-line 6 engine has powered millions of Jeeps, including CJs, Wranglers, Cherokees, and Wagoneers. The 4.0 delivers adequate horsepower from the factory, but many off-road drivers want more horsepower and torque to conquer challenging terrain, which means these engines are often built and modified. The Jeep 4.0, or 242-ci, is affordable, abundant, exceptionally durable, and many consider it one of the best 4×4 off-road engines.

In this Workbench title, veteran author and Chrysler/Jeep engine expert Larry Shepard covers the rebuild of an entire engine in exceptional detail. He also delves into popular high-performance modifications and build-ups. Step-by-step photos and captions cover each crucial step of the engine disassembly. He shows the inspection of all critical parts, including block, heads, rotating assembly, intake, and exhaust. Critical machining processes are covered, including decking the block, line boring, and overboring the block. The book provides exceptional detail during the step-by-step assembly so your engine is strong and reliable. Installing a larger-displacement rotating assembly (or stroker package) is one of the most cost-effective ways to increase performance, and the author covers a stroker package installation in detail.

With millions of Jeep 4.0 engines in the marketplace (which are subjected to extreme use), many of these engines require a rebuild. In addition, many owners want to extract more torque and horsepower from their 4.0 engines so these engine are also modified. Until now, there has not been a complete and authoritative guide that covers the engine rebuild and build-up process from beginning to end. Jeep 4.0 Engines is the essential guide for an at-home mechanic to perform a professional-caliber rebuild or a high-performance build-up.

From the Publisher

The venerable Jeep 4.0-liter inline-6 engine has powered millions of Jeeps, including CJs, YJs, Wranglers, Cherokees, and Wagoneers. With millions of Jeep 4.0 engines in the marketplace (that are subjected to extreme use), many of these engines require a rebuild. In addition, many owners want to extract more torque and horsepower from their 4.0 engines so these engines are also modified. This complete and authoritative guide covers the engine rebuild and build-up process from beginning to end. Jeep 4.0 Engines is the essential guide for an at-home mechanic to perform a professional-caliber rebuild or a high-performance build-up.

Engine History

The Jeep Wrangler (and CJ and TJ) models and the Cherokee models have relatively short wheelbases, which yield short engine compartments. The inline-6 design tends to make for a long engine. In addition, all 1986 and newer 4.0 engines have high-tech emissions systems. All 4.0 engines also use multi-point fuel injection (MPI). This adds up to a very cramped and busy engine compartment.

Engine Removal

You need to disconnect the throttle linkage, wiring harness, hoses, and other miscellaneous parts, and then you can pull the engine. Once the engine has been pulled, the engine rebuilding truly begins.

Engine Disassembly

At engine disassembly, the intake manifold can be removed without taking the fuel rail off or the injectors out. Consider setting the manifold assembly aside until later. To remove the fuel rail from the intake manifold, gently rock the rail until all injectors are out of the intake manifold. Place one hand on each end of the fuel rail. Apply pressure in the same plane as the injector centerline.

Inspection

You need to look for telltale signs of problems and wear. Used engines don’t have pretty, shiny combustion chambers and valves but they can tell you a lot about the engine’s history and condition. It is good to look at all of these parts before you clean them too extensively.

Performance Crate Engines

The most popular crate engines are based on using the long-stroke crank (3.895 inches) in the 4.0 engine, which makes a 4.6 or 4.7 engine depending on the specific amount of over-bore used in the engine. Large-displacement crate engines are offered by Hesco, Titan Engines, Golen Engine Service, and others. Front hardware, such as the vibration dampener, front cover, and thermostat housing, is optional. In addition, the intake manifold, exhaust manifold, and valve cover may not be standard. This engine was built by Godfather Racing.

Parts Selection

All 4.0 engines used pressed pins in the pistons. Floating pins require pin locks on each end of the pin and the locks require that a groove be machined into each pin boss (shown). Many aftermarket pistons are machined with pin-lock grooves and if you use pressed pins you do not install the locks.

Building Stroker Engines

The large, round hole in the center is the bottom of the cylinder bore. No clearance notch is required for the 3.895-inch stroker crank. The wall of the crankcase is at the right and also does not need to be notched for this stroker crank. Strokers longer than 3.895-inches may require clearance notches in these areas.

Pre-Assembly

This is the cutter sitting on the pilot that has been inserted into the valveguide. The ball on the top with the two ears adapts to the head of the machine and allows it to lock in and drive the cutter. Except for the drive head, this cutter is ready to machine the exhaust valveseat.

Final Assembly

The oil pan gasket comes in four pieces: one for each end, one at the top, and one at the bottom. Match the shape to the bolt pattern. The rear seal is round and fits easily. The front one is much more difficult. Check the lower left corner just ahead of the bottom side gasket; add a dab of RTV. You need to spread RTV across the whole surface of the front cover to hold this gasket in place.

Publisher ‏ : ‎ CarTech; Illustrated edition (September 19, 2014)
Language ‏ : ‎ English
Paperback ‏ : ‎ 144 pages
ISBN-10 ‏ : ‎ 1613251386
ISBN-13 ‏ : ‎ 978-1613251386
Item Weight ‏ : ‎ 1.05 pounds
Dimensions ‏ : ‎ 8.5 x 0.38 x 11 inches