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Back in the April 2003 issue of Engine Builder information was provided about the proliferation that occurred on the engine blocksof 4.0L Jeeps starting in 1996 and continuing though the present.Sound familiar? Well, you may remember the reference made to Popeye andhis "Jeep" friends.

The 4.0L came on the scene in 1987 and is still being used, however2005 was the end of the journey in domestic production. This is an old schoolinline six with lots of torque and there are still many of them out onthe road. Plenty of opportunity for you to see them.

This time we are going to take a look at the cylinder heads for the4.0L Jeep. There are four of them and you really cannot swap themaround, so you had better know what you have and what fits where.

All years of 4.0L production used cast iron cylinder heads. In1987-1990 the cylinder head casting number is 2686. The fastest VIP(Visual Identification Point) on this head is the mostly rectangularshaped intake ports (see Photo 1) that have an abnormal looking reliefat the top for injector clearance. Note also that the intake ports arefacing each other on the front two and rear two cylinders but theexhaust do it on the center two. The exhaust ports are a rounded "D"shape.

The 1991-1995 head castings (c/n 7120 and 33007119) appear identical tothe 2686 until you get to the port side of the cylinder head. There,you’ll discover the VIP to be the intake port which now has muchsmaller relief for the fuel injector and the exhaust ports now looklike a squared off circle or a rounded off square depending on yourperception (see Photo 2).

From 1996-1999, the Jeep 4.0L used head casting 0630. This cylinderhead has two receiver holes for two dowel pins that were added to theblock for cylinder head alignment (see Photo 3). The intake ports werechanged once again, and there was a newly designed rocker cover andgasket on the scene, that will not retro back. Also, the move was madeto lighter pressure beehive-shaped valve springs and a differentprofile cam.

Note in Photo 4: the center exhaust ports on this head run off a commonport without a divider at the gasket surface. This is the quickest VIPof this head.

The 1999-2005 cylinder head has casting number 0331, and includes thesame two head dowel receiver holes. Surprise, surprise: the intakeports have changed once again. As seen in Photo 5 they havegone back to that small relief at the top type port again, and the exhaust ports are the smallest that they have ever been.The interior of these ports are very rough "as cast" and are very easyto recognize. However the VIP on this head is the spark plug side ofthe cylinder head where there are four new bosses to mount the coilpacks (Photo 6).

That should get you through the 4.0L Jeep heads and keep you out of the"do-over" column. Photo 1Photo 2Photo 3Photo 4Photo 5Photo 6

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Roy Berndt
Roy Berndt has decades of machine shop experience. He is the Program Manager for PROFormance Powertrain Products, a PER in Springfield, MO. You can reach Roy at [email protected]