Six Cylinder 4.2 Liter Jeep engine Specs

Six Cylinder 4.2 Liter Jeep engine Specs

All Jeeps with the 4.2Liter engine
Published by TerryMason
11-19-2005

Six Cylinder 4.2 Liter Jeep engine Specs

The popular AMC 258 inline 6 4.2L engine was introduced back in 1971, and was used in various pickups and Wagoneers. In 1972 the engine was avaliable in Jeep CJs, and eventually made it's was into Wrangler YJs until it was phased out. This engine produced gobs of torque, was reliable, and inexpensive.

The carburetor (Carter BBD) that was chosed for this system, and it soon became very unpopular. It used a pulse air system that was a mess of air hoses.

#1 (permalink)

By TerryMason on 01-27-2008, 10:53 AM

Six Cylinder 4.2 Liter Jeep engine Specs - Technical specs

Displacement	256 cubic inches	Click below to see the Vacuum curve
Cylinder numbers (front to rear)	1-2-3-4-5-6
Firing order	1-5-3-6-2-4
Spark Plug gap	0.033 to 0.038
Ignition timing	9 to 11 degrees
Idle speed (auto)	600 +/- 70 rpm
(manual)	680 +/- 70 rpm
Engine oil	API SE of SF
- Oil capacity	6qts
Automatic Transmission Fluid	Mercon ATF
- ATF Capacity	4qts

Engine	Transmission	Initial Timing at Curb Idle (Vacuum Hose Disconnected)		Curb Idle Speed RPM
Engine	Transmission	Set To	Acceptable Range	Set To	Acceptable Range
258 1 Barrel carb	Manual	3° (49)	1° 5°	850 (49)	750 950
		10° (Alt)	8° 12°	600 (Alt)	500 700
		8° (Cal)	6° 10°	850 (Cal)	750 950
	Automatic	8° (49)	6° 10°	550 (49)	450 650
		10° (Alt)	8° 12°	550 (Alt)	450 650
		8° (Cal)	6° 10°	550 (Cal)	450 650
258 2 Barrel carb	Manual	6°	4° 8°	650	550 750
258 2 Barrel carb	Automatic	6°	4° 8°	550	450 650

#2 (permalink)

By ricroz on 12-06-2009, 09:31 AM

Re: Six Cylinder 4.2 Liter Jeep engine Specs

Coverted my 1986 AMC Eagle to Howell TBI fuel injection last year. Ended up with a much better running engine and a garbage can full of useless hoses and emmisions control junk. I understand AMC was about to move all it's cars to FI when the company folded in 88.

#3 (permalink)

By carnuck on 12-06-2009, 10:23 AM

Re: Six Cylinder 4.2 Liter Jeep engine Specs

They had TBI in '86 (My Comanche 2.5L has it) and were about to put it into the Eagle SX4s but when Chrysler took over, they nixed the idea and designated the AMC version of the Eagle to the trash pile, then sold the name to Eagle Mitsubishi a couple years later.

The AMC 6 cyls had 2 different bell patterns that changed in '72 to match the AMC V8s. Prior to that they had their own small pattern and '71 is the only year for 258s with the small pattern (they lived on in Industrial use and Postal trucks a few years more)

In '71 the block was made taller for a longer stroke. The 258 is the early 232 with a longer stroke. The '71 up 232 is a 199 with longer stroke. They did the same thing with the V8 motors.
343 became 360, 290 became 304 and 390 came out, they modified the block (extra webbing and beefing up) to make the 401.

The 258 had 2 other relatives besides the 232. In Mexico they had a 282 and a 262 made by making the bore larger (new block)

#4 (permalink)

By DIRTY-CJ on 01-12-2010, 10:43 PM

Re: Six Cylinder 4.2 Liter Jeep engine Specs

Yuk! I have the 258 I-6... I went witrh the offenhauser intake mani, Holly truck avenger (I jetted it down to about 270) pacesetter headers with magna flo exhaust. It now runs like a raped ape I love it!