In this article I am going to explain the basic fundamentals of a not-so-hard shadetree mechanic head conversion on a 4.2L 258ci engine block. As I'm sure any Jeeper knows, these are the engines that mainly came in the CJs and early YJs. After several months of research, I came upon some discoveries about putting a 4.0L head on a 4.2L block. Apparently the block on a 4.2L and 4.0L are very similar except the 4.2L has a longer stroke and a few design differences. After I sent several e-mails trying to find out more information about this conversion, I was informed that this conversion is possible and can provide a 40HP gain. That's right, 40HP! I was a little surprised myself. Not only does this conversion add more HP, but I have read that people have experienced a substantial increase in gas mileage; approx. 17-18%.

I began searching for a 4.0L head and found just what I was looking for at Koller Dodge (check their website for more details). They provided a remanufactured head, completely rebuilt and basically new. From here there are a couple of retro-fit modifications needed to make this work right. Don't worry, they don't require any difficult procedures or special tools. Below is a picture of my new 4.0L head upon arrival via UPS.

PARTS LIST:

REMOVAL OF OLD 4.2L HEAD:

This part was a dream come true. I have wanted to remove the old head and intake system for as long as I've owned the Jeep. I started by removing the air cleaner, valve cover, power steering pump, radiator hoses, etc. NOTE: I didn't remove the Carter carb and intake yet because I had other plans involved with the intake system. (Check next months issue for more details) Anyway, after removing the rocker-retaining bolts and removing all of the rocker arms and rods, I then removed the head bolts. Now the old 4.2L head is ready for removal. The pictures below show the head removal process.

INSPECTION AND CLEANING:

After the 4.2L head, intake, and carb was removed, I was really surprised to see how clean the cylinder walls and pistons were. This engine currently has 98,000 miles on it and appears to be in really good condition. I was afraid that I would discover some problems upon removing the head like excessive carbon build-up or scratched cylinder walls. I guess it makes sense since the engine never burned oil. Well anyway, I cleaned whatever I could while the head was off. I scraped off the entire surface before installing the new head.

INSTALLATION: PART 1:

The first step is to prepare the head for installation. After you've obtained all the parts from the parts list, you will need to perform the following task. In order for the 4.0L head to work on the 4.2L block, I had to fill in a couple of water jackets in the 4.0L head. They are the small triangular water jackets on the same side as the intake. These must be filled because on the 4.2L block these water jackets don't exist. I made a couple of calls and came to the conclusion that the best way to fill these holes   is to use a high temp epoxy putty. I bought two tubes of QuikSteel. This is a 500 degree max temp super strength epoxy putty found at most auto parts stores.

Since the holes in the head expand inside it makes it much easier if you use foam-packing peanuts to fill in the holes. I used one packing peanut for each hole. This makes applying the epoxy much easier. Don't worry, the foam peanut will dissolve. After filling in the holes, make sure there aren't any burs or pieces of epoxy sticking up above the head's surface. I used some fine sandpaper to ensure the head would match perfectly to the head gasket. It's very important that the head is completely smooth to ensure no head leaks, compression loss, or blown head gaskets, etc. Below are some pictures of the holes filled in.

   

   

DIAGRAM 1.3

This diagram shows exactly which holes need to be filled on the new 4.0L head in order for the conversion to work. NOTE: It's very important that you plug only the holes that are shown in the diagram. If you accidentally plug additional holes in the head it could cause your engine to overheat or cause other problems. See diagram below for details.

INSTALLATION: PART 2:

After the preparation of the head is complete, you're ready for the installation of the new 4.0L head. I suggest having a friend help place the new head on top of the 4.2L block. The head alone weighs 77lbs and when you're trying to line up the head on the block while also trying to align the head gasket all at the same time, it would be very difficult as a one man job. I started by placing the new head gasket on the 4.2L block, then with the help of my friend Nate, we lowered the head down onto the block. It was surprising how well the head lines up.  It appeared to fit as perfect as the 4.2L head.

     

          

 

INSTALLATION: PART 3:

After placing the head onto the 4.2L block, it's time to mount it down. It's recommended that you use new head bolts because of accuracy, but the old head bolts will still work. For my application, I used the old head bolts. A new set of cylinder head bolts are $17.00 from Mopar Performance (Part #: 4529204). I was unable to find new head bolts in time for the installation. It's very important that you torque the head bolts down in order and to the right torque specifications.  I created a little diagram below to view. A similar diagram can be obtained in a Haynes or Chilton's repair manual.   The first round, you want to torque the head bolts down to 22lbs of pressure. (I recommend using a quality torque wrench for better accuracy). On the second round of tightening the head bolts, torque them to 45 lbs of pressure. On the last round, tighten all the head bolts to 110 lbs of pressure except head bolt #11, you must torque this bolt to 100 lbs of pressure. NOTE: Before installing the Number 11 head bolt, put some Loctite 592 sealant on the bolt. All these torque ratios aren't custom or created for this installation; these are basic head bolt tightening specs, and can be obtained in your Jeep repair manual as well. Click on Diagram 1.1 for printable size.

Diagram 1.1 Torque Sequence

 

INSTALLATION: PART 4:

The next thing to do is install all the rods and rockers. When doing so, you will want to set the engine at TDC (Top Dead Center). This means the number one piston must be at the top of the cylinder. To obtain this, you must move the harmonic damper until the mark is directly pointed at the 0 position on the timing settings. After the motor is verified to be at TDC, place the rods into position as you took them out. After placing all the rods back into position, mount the rockers back on as you took them off. When bolting the rockers down, it is very important that you don't under or over tighten them. The dealership recommended torque specs say to torque them to 19 lbs.

Now that the head is in position and mounted, you can place the valve cover on. Be sure to use a new cork valve cover gasket. I'm not sure of the torque specs for the valve cover, but it's specified in your Haynes repair manual. Check your Haynes or Chilton repair manual for exact specs. Below are some pictures of my Jeep with its new 4.0L head and valve cover mounted in position.

 

           

           

INSTALLATION: PART 5:

Now that the 4.0L head is mounted and ready, you're going to need a 4.0L header or exhaust manifold. For my application, I had a friend that had a spare 4.0L header from an 88' Jeep Cherokee lying around. Since my project is on a budget, I put this header on for now. I highly recommend using a Borla header. Be aware that the intake manifold and exhaust use a lot of the same mounting bolts. There is no need to customize anything, except you'll need to mount the intake manifold and exhaust at the same time. There is also a specific torque sequence and lb. amount for these bolts as well. I created another chart to specify these torque sequences. Torque the intake/exhaust manifold to 23 ft/lbs. (Click on Diagram 1.2 for printable size)

Diagram 1.2 Torque Sequence

   

INSTALLATION: PART 6:

After completing the installation of the new head, it's recommended that you use different spark plugs. For my Jeep, I bought Bosch Platinum platinum +4 plugs. They're a little more expensive than most and I'm not sure if they will even make a difference, but I figured I would give them a try. Torque the spark plugs to 27 ft/lbs.

INSTALLATION: PART 7:

From here, put your carb back onto the intake manifold including all the vacuum lines, fuel lines, etc as you took them off. Hopefully you marked all the hoses and lines so that they can easily be put back in their proper locations. If not, the vacuum diagrams can be obtained in the Chilton or Haynes repair manual. Everything should bolt right back into position except the rear power steering pump mounting bracket. This needed a little modification, which is pretty self-explanatory upon installation.

4.0L HEAD CONVERSION FINAL EVALUATION:

The overall conclusion of my 4.0L head conversion was definitely two thumbs up. The cost was fairly inexpensive compared to the amount of power gained. Although I've done minor engine repairs and modifications before, I have never done anything even remotely close to this and, to my surprise, it was pretty easy. The overall preparation, old head removal, and new head installation took about 5 - 6 hours. This may vary depending on the tools used. I can't say exactly my overall results of the power since I'm currently adding additional engine modifications. (See next months issue for more details). I can say that from speaking with fellow Jeepers on the Internet that have performed the same conversion the overall performance increase is substantial and well worth the time.

TO GET STARTED ON YOUR 4.0L HEAD CONVERSION, CONTACT KOLLER DODGE AND THEY CAN HOOK YOU UP WITH A REMANUFACTURED HEAD AND NECESSARY PARTS TO CONVERT YOUR JEEP. SEE INFORMATION BELOW FOR DETAILS.