Excerpts from Robert C. Ackerson's book: The 50 year History of the Jeep

ISBN: 0-85429-533-x

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pages 262ff: The Cherokee/Wagoneers: 1984-1988

GENERAL

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It was evident, just by a brief review of American Motors' 1984 Annual Report that new era for Jeep had begun in 1984.

...

Work on these new Jeeps began in min-1979 and represented an investment in excess of $250 million in tooling and equipment...

...a new "UniFrame" body design in which a full-length boxed steel frame member was welded to the floor panel of its unitized body structure. This provided both a relatively light construction weight and an extremely rigid body as well as an optimum level of interior space utilization.

...The result was impressive. Motor Trend, September, 1983 concluded, "the Cherokee handles with much greater agility and stability than you expect from a 4wd truck, for it rides with astonishing smoothness for what is a relatively lightweight vehicle."

...Standard was Command-Trac... part-time...New Process 207, all-aluminum two piece casing. ... Select-Trac, in addition to its viscous-clutch and limited slip center differential (a New Process 229 model) was also fitted with a differential lock in Low Range for added durability. It was suitable for full-time 4wd operation under all traction and road conditions. The transfer cases for Selec-Trac and Command Trac had the same 2.62:1 Low and 1.0:1 High Range ratios.

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ENGINE:

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Quite literally powering this banner Jeep year was the first 4-cylinder engine ever designed by American Motors. While not related in any way to the original L-head Go-Devil and F-Head Hurricane engines this in-line, overhead 4 cylinder was their worthy successor.

American Motors devoted three years to its development and, noted Roy Lunn, "unlike most engines available today [it] was not designed for passenger cars and then adapted for trucks. We specifically developed it with our Jeep vehicles and Eagle in mind. That's the reason that performance and durability were of such prime consideration from the very beginning."

Although some of components were interchangeable between the AMC 258 cubic inch 6-cylinder and the new engine, the 4-cylinder was not (john's note: note the NOT) a cut down version of the big six. Noted Roy Lunn, "There is some common competency, but the 4-cylinder includes many unique items such as its own electronics systems. It also has a shorter stroke and larger bore. The valves are larger and the pistons are new."

Compared to the 258 engine's 3.75 inch bore and 3.9 inch stroke the four's respective dimensions were 3.875 and 3.188 inches for a displacement of 150.4 cu in or 2.465 liters. Commenting... Roy Lunn recalled:" We wanted as much displacement- for power and torque - as possible within the confines of bore centers of the tooling. The only parameter we could influence substantially was stroke. So we picked the largest bore and stroke in order to get 2.5 Liters."

The crankshaft was supported in five main bearings, hydraulic lifters were operated by an overhead valve arrangement and both the cylinder head and block were constructed of cast iron. The pistons were manufactured from Autothermic aluminum with steel struts. A relatively high, 9.2:1, compression ratio was attained by use of a double-quench combustion chamber. When fitted with base accessories the engine's dry weight was 315 pounds.

When options such as air conditioning and power steering were used a serpentine belt system replaced a V-belt arrangement. In that form the engine weighed 341 lbs.

(skipping a bunch of stuff)

... Manufacturing of AMC's 2.5 liter engine took place at its Kenosha, Wisconsin facility where the 6-cylinder and V-8 engines were also built. Maximum output was 195,000 units annually.

All models were available with an optional (priced at $305) 173.2 cu in 60 degree V-6 engine supplied by Chevrolet. (john's note: and that $305 would be paid again and again in repairs. The resale value of XJ's with this motor is significantly lower than models with the later in line 6. I've dumped EVERY XJ I had with a V-6 within about 3 months...)

(lots more cool stuff in this book I don't feel like typing...)

(I also noticed that the early little wagoneers did not have the spider eyes (4 headlights) until 1986...)

(In 1986, the 4wd, 4dr cherokee based at $11,320, the wagoneer at $13,630, and the wgnr limited $18,600)

............

By the mid-eighties it was apparent that the age of high performance was alive and well in the US.....

But even long-time AMC fans weren't ready for what AMC had in store for the 1987 Cherokee, Wagoneer and

Comanche models.... It was, therefore, with justification, that AMC, on 8 September, 1986 announced: "With the introduction of its new electronically fuel-injected, 4.0liter 6-cylinder engine ... American Motors is poised to deliver the most potent 1-2 power 'punch' in the light truck industry in 1987."

The superiority of this engine over its competition was so overwhelming that Chris P. Theodore, AMC director of engineering predicted that "Every aspect of this engine is so appealing, we expect Cherokee, Wagoneer and Comanche buyers will choose this option overwhelmingly..."

The specifics of the new AMC engine were dazzling: a displacement of 242 cubic inches (larger than any other 1987 light truck 6-cylinder engine) and peak outputs of 173 horsepower at 4500 rpm and 200 lb ft of torque at 2500 rpm. This translated into a zero to 60 mph time of less than 10 seconds and increase in ...maximum towing capacity to 5000 lbs....

At first glance, the new engine outwardly resembled the older carbureted 258 cu in (4.2L) 6-cylinder (it will be recalled that the I-4 engine and the 258 cid 6-cylinder had common bore centers, valve locations and general front arrangements). In reality, therefore, a closer relation was the fuel injected I-4 introduced in 1986 since it utilized most of that engine's design and performance features. For example, the complete combustion chamber from the cylinder head to the piston cavity, as well as the bore center were transferred from the I-4 to the 4.0 L 6-cylinder. In addition, the intake and exhaust port shapes from the 4-cylinder were utilized. AMC engine engineers also selected the block height of the two engines so that a common rod, piston pin and piston compression height could be interchanged between the two engines. Other parts shared included rod bearings, main bearings, oil pump, piston ring set, pistons, head bolts, rod cap bolts, main bearing caps, valve stem seals, spring retainers, keepers, rocker arms, pivots and fasteners and the hydraulic valve lifters.

The 4.0 liter engine's cast iron cylinder block was similar to that of the 4.2L engine which had a thin wall casting except for an increased bore diameter, longitudinal stiffening ribs, the addition of tin for improved wear and some minor boss revisions for external attachments.

A major contribution to the new engine's high power output was it's increased valve area as compared to the I-4. It's intake valve diameter was 1.91 inches instead of 1.79 inches. The exhaust valve diameter was increased from 1.41 inches to 1.5 inches. In combination with high-flow intake ports these changes provided substantially higher air capacity. The cylinder head continued to be cast iron but it now had a cast aluminum cover. The head gasket was upgraded from embossed steel to a composition with tin-plated steel fire rings. Although the cam had a common profile with the 4-cylinder engine, it had increased lift and extended duration that resulted in a high volumetric efficiency at high rpm. Other details changes included an alloy sintered iron cam sprocket set and roller chain, and tri-metal (copper, lead plus overplate) instead of bi-metal connecting rod bearing. The bore and stroke of the 4 L engine were 3.875 and 3.44 inches respectively.