At 100,000+ miles the 4.0 in my ‘88 Cherokee is still running strong. Yea, I have had the standard attrition of any 100,000 mile engine of alternator, water pump, A/C clutch and such, but overall the motor is very solid. If I were a bettin man, I would imagine I have another good 60 to 80,000 miles before needing to do a head job or cylinder work. But, you know, there’s always that possibility that I could have some major internal failure sooner. And I sure would like to eke out a little bit more horsepower, and 100k is 100k.

Ah heck, if I get a builder now and spend some time, instead of having to do it at the last minute, I just might be able to cut cost and build a real power house. OK, enough rationalization! Just had to get that out of the way up front. The concept here is to do just that, cut cost and still build a real performer out of a 4.0. By planning ahead and spending time doing each item correctly, and as many as possible yourself, it is possible to build a high performance engine at a relative low cost. Now, lets talk relative low cost.

As the old racing adage goes “How fast you want to go is directly proportionate to how much you want to spend”. I have always subscribed to this line of thinking. Where I hope to cut cost are in areas that I can do myself, and avoid paying someone else for, and in researching my best cost vs. performance improvements to be implemented.

This series of articles will chronicle that attempt. Let me say up front that although I have spent many years working on and around engines, even swapped a few out. Aside from the occasional head removal I have never broken an engine totally down and started from scratch, well OK except for a lawn mower or two that I never intended to put back together again anyhow! This will be a learning experience for me as well as a great chance to get ahead of the game on preparation for my inevitable need for a new engine in the future.

I hope you will all hang in there with me over the coming months. Remember, I’m a working stiff like the rest of you. Unless I get real lucky and find a sponsor, I will have to end up paying for all of this myself. I imagine, just like everyone else, money and time will get in the way as I go along, but I will try to have some form of update in each issue along with pictures and sidebars.

So if were all ready, here we go!

Engine History & Specifications

First and foremost, we need to understand the history behind the 4.0 and some of the model variables that need to be taken into account. To my wife’s great agitation, I can not start a project of any magnitude without learning everything I can about what I’m doing. Therefore, I have at least one book on each and every major project I ever started. My book shelves look like a Time Life series reject, because I only get the books I need.

So I went two routes here, first I ordered “Jeep Engines, Speed Secrets & Racing Modifications for Jeep-Built 4,6 & V-8 Engines” from Mopar. This is a great reference book! It is also advisable to have a good Chilton or Haynes service manual handy and I will probably also order the Chrysler engine manual. I also started contacting companies that specialize in Jeep engine performance modifications, and learned some of the variables with these motors. My biggest hindrance has been and will be that I am starting this project with V8 power building preconceptions, and those don’t always transfer to other cylinder configurations.

There were two iterations of the 4 liter engine, the 4.0 and the 4.2. Both are cast iron in-line 6 cylinder engines. The 4.0 has a displacement of 243 cubic inches and the 4.2 a displacement of either 232 or 258 cubic inches. I will be focusing on the 4.0, but there are only small differences between the 243, 232 and 258.

4.0 Engine Specifications

First of all, in ’91 the head and intake were redesigned to flow better. There is about a 15-20 hp difference in the new design. Unfortunately the wiring harness was also completely changed at this time. The big positive here, if I were to upgrade to the newer head and intake design, is a big decrease in under hood wiring and hoses. It seems that many of the emission control items were integrated into the new design, negating the need for all the hoses and wires.

I looked into the possibility of doing the rewiring, but soon discovered that it was way over my head. There is a local shop that specialized in Jeep engine conversions. They had done this type of conversion and would provide the rewiring for a reasonable $500. I would also have to get a ‘91+ computer, another $500, and I would not be able to reuse many of my existing external components, like the intake manifold and such. After contemplating this type of work, and a minimum $1000 to $1500 investment, for a 15-20 hp gain, I decided to stick with my pre ’91 design.

The second major change is in the ’96 model. The webbing on the block was reinforced. This made for a stronger block and truer cylinder walls. Evidently, earlier 4.0 blocks had a tendency to warp or torque slightly causing some knocking. Again unfortunately, the ’96 block is not compatible with much of what I have in my engine compartment, and I would be back to the ‘91+ electrical problems, so its out.

This left me with an original pre ’91 block and head combo. Since I now knew what to look for, I needed to know how to look for it. I needed to check the engine build date code machined on the right side of the block between the number 2 & 3 cylinders. This code is just below the spark plug holes is laid out like this:

401MX12

• 4 = Year (1994)
• 01 = Month (January)
• MX = Engine Type/Fuel System/Compression Ratio (MX is a 243 CID, multi-port fuel injection system with 8.8:1 ratio
• 12 = Day of month of engine build

• P = One or more connecting rods bearing journals
• M = All crankshaft main bearing journals
• PM = All crankshaft main bearing journals and one or more connecting rod journal

• B = All cylinder bores
• C = all camshaft bearing bores

Now knowing what I was looking for and how to look for it, its time to start checking into possible sources for my rebuilder.

Project 4.0, Buy & Check

I approached the next phase of this project with two things in mind. Buy low, Build high! What I mean by this is try to find the best deal that I could find on a rebuildable engine and build spend the saved money on high quality parts. Secondly, I will detail the areas of concern as they relate to basic preparation of the block and head for our upcoming build. What items should be checked, and what checks should be performed and what tolerances we should be looking for.

Buying a Rebuilder Trying to keep to the Buy Low concept of rebuildable engine buying can be a "Damned if you do, and Damned if you don’t" type of deal. Your "Damned if you do", if you get a lemon. Your "Damned if you don’t", if you pay for rebuilt parts you will eventually discard.

Here’s what I mean by this statement. I could go out and get a deal on a junkyard block and head, or I could get a rebuilt engine from an engine shop. The junkyard route is the toss of a coin as far as the possibility of getting a lemon. Although, most reputable yards now give a short term warranty. The engine shop offers more of a guarantee on the quality of the block and head but the trade off is ending up with factory pistons, rods, rockers, and lifters and run of the mill, mill work. I really wanted to build Project 4.0 with the best available parts I could afford. So I was really leaning toward finding a rebuildable engine rather than a prepared engine.

To be fair, I gave both paths a shot. I called to get pricing from numerous local junk yards and an equivalent number of engine shops. I’ll get to prices in a moment, but the first thing I found is that 4.0’s are just too reliable! No one had one in stock. From the sound of most of the people I talked to, they thought the likelihood of me finding one to rebuild was on their “slim to none” scale. Interestingly enough I found out that the engine shops worked on the same scale, since they normally wanted a core to sell me an engine. No excess cores, no available engines. Also, without core the price soared! I started getting discouraged before I had even gotten a chance to start. I went ahead and had them give me a non-core, or without exchange, cost for the engine.

Clean and Check

OK, I had my base engine, now what. First of all, I wanted to get both the block and head totally broken down and take the parts I was to keep and have them cleaned and checked. I may be particular, but if I can, I always like working on something that’s fairly clean. Some would say to wait until having the mill work done to have the parts vatted, or cleaned, but I wanted to take a good look at everything without a mile of grease and rust in the way. The argument here is that after vatting the parts will start to rust again. My planned cure to this was to cover everything after vatting with WD-40.

Since I didn’t have an engine stand that was first on the agenda. I looked around town for a good deal and ended up with one from a local discount parts house for $60.00. It actually was pretty well made for being this cheap. I loaded the block onto it and removed the pistons, rods, lifters, crank, bearings and cam. The only thing on the head was the valve springs and valves. A valve spring compressor runs about $25. After some checking I found that it was cheaper to just have the machine shop remove them when I took it in to be vatted. They would put the new ones on when I had the valve job done, so the compressor was not really needed.

The only note I feel compelled to make here is in relation to the crank clearances and piston deck height. In reading the Mopar Jeep Engine Secrets book they mentioned how important it was to check and record piston deck height and crank clearances. Mainly the deck height is important as it has direct influence on compression ratio. I did not do this because I was not planning to reuse the pistons and planned to have the crank turned. My reasoning here, right or wrong, is that the new piston deck height and the turned crank clearances would not be even remotely close to the original clearances. I guess time will tell if I boned up here!

At this point I had every thing out of or off the block and head except for the freeze plugs and screw in plugs. I tried to remove these my self, but could not get them to budge. The prescribed method on a freeze plug is to use a dent puller, didn’t work. On the screw in plugs the idea is use of a allen wrench, didn’t work either. Again, discretion is the better part of valor. I decided to let the machine shop remove them for a minimal charge, actually I don’t think I was charged for this.

I dropped of the head, block and crank at the machine shop with the express instructions to vat them all and check all of the tolerances. What I was looking for was how much I needed to bore the block, how much the crank would need to be turned and was the head true and millable. I also wanted them to check for any cracks or other unseen problems.

A local shop, near my home, happened to have a good reputation for this type of work. It took them a few days, due to other work, to get my parts vatted and checked. What I ended up with was, the block needed to be bored 30 over and the head needed a valve job but looked good overall. The crank was another story. It was going to need a 10/20 or possibly a 20/20 turn, which is not good. What this means is that the crank bearing journals would have to be turned 10 to 20, 1000’s of an inch. The first number refers to the main bearing journals and the second to the rod bearing journals. My understanding is that a 10/10 or 10/20 is not too bad and would just require oversized bearings. This goes up from there and bearings are made for even higher grinds. But for a performance applications a 20/20 grind would be pushing it, and my crank was iffy on this point.

Therefore, I had to come up with either a new or better crank for my application. Total cost for vatting, valve spring/valve removal, freeze/screw in plug removal and check out was $60.45. Already I was getting into the “Damned if you do” part of my equation. If you get your rebuilder from either a salvage yard with a warranty or a motor shop you can simply take the crank back to be replaced. But, since I had gotten a deal on mine, I was not inclined to gripe about it. What I did do is go back to where I got it to see if they had a line on another one that I could get. The fact that I kinda know the guy from other Jeep discussions helped here. He checked with a number of his sources and I should know this week if he has a replacement for me.

Now that I know what needs to be done, I want to plan for the parts that will go into the build and start the honing process. I will probably make a parts manufacturer selection prior to honing to ensure proper fit. With the valves and springs this will be a necessity. Here are some other basic preparation items, taken from the Mopar Jeep Engine Speed Secrets book, that also need to be addressed at this time.

• Probably a good idea to get new head bolts. Screw them into the block without the head. Inspect the rows of bolts to ensure that none are bent, none of the holes are drilled at an angle or are too shallow and record the thread engagement.
• Main bearing bores should be checked for both specified diameter and alignment with each other.
• Ensure all dowel pins used for alignment are the proper height and are locate the head properly. This is best done after the head is milled and without the gasket in place.
• Rear main bearing oil seal machined grove should be roughed slightly with a center punch.
• Make sure all oil holes are clear and clean.
• Wash the block out thoroughly with solvent and use bottle brushes to clean out all bolt holes , oil passages, ect.
• Using a fine stone, deburr any rough edges or burrs from casting.
• Go over ever part inch by inch and make sure that all contaminants are gone and there are no metal shards from the honing process.

Basically this is the time to get everything clean and straight. The basic building block that the Mopar book stresses over and over is that you have to start with a clean and straight environment. Its the only way to make horsepower.

One last issue here. If you plan to go ahead and get the mill work done at this time it is important that you use a Mopar honing plate. Check with the machine shop to make sure that they plan to use a honing plate for the 4.0 or spend the $50 to get your own and make sure that they use it. The bore needs to be straight and the best way to ensure this is to use a honing plate. If all the bores are not straight you will not be able to make maximum horsepower and piston slap could be more probable.

In the next issue I will put the engine plan together. What I will be looking for is to make the most horsepower with the least expense both in cost and driveability. Until then, I?ll get to cleaning!

Project Plan

Research

The hardest part, as I have found, of this entire project has been finding solid information on 4.0 builds. As far as I could find, there are only a handful of people who really know how to build a 4.0. As sure as I make this statement and publish this, I will get 50 E-mail's from knowledgeable Jeep builders. Be that as it may, my search for knowledge has been frustrating. Luckily through this process I struck up a conversation with Terry Craig, who proved a wealth of information on 4.0's. Thus, a relationship was born and now Terry will be a regular writer, starting off with a split of this project into two. Terry will build a wild version, while I build a milder version of the 4.0.

Another problem is the small number of companies who build aftermarket performance engine parts for the Jeep. Basically, I found three. Mopar Performance, HESCO and Clifford. Of these I have contacted Mopar, and gotten no response yet , and HESCO. I expect to contact Clifford in the next week or so. I also talked to numerous Jeep builders and other ex-Chrysler tech's and engineers to gain as much information as I could before settling on a plan. The most frustrating wall that I have run up against is either people's lack of information, their unwillingness to divulge what are obviously closely held speed secrets, or abject rejection. Interestingly enough I have had more people tell me that its a waste of time to try to build a 4.0 than I have had give any constructive information. "Go stock" seems to be the call of the day. Probably this has more to do with emission issues as with anything else. I truly believe that many builders have gotten shy to doing this type of work due to the hassles that can come about from high performance builds.

It is true that you must approach building a performance 4.0 differently than a V8. The same rules don't apply. Probably the single largest factor that denotes this difference is that almost to a man I was lead away from a cam change. The staple of a basic performance build with almost any V8 is a hotter cam. Not so with the 4.0. Problems with vacuum pressure and fuel mixture seem to be possible with cam changes in the 4.0. I did get a tidbit of information about the possibility of the new TJ cam producing a bit more HP and torque. I am still researching this though, and will report on it as soon as I have solid information.

Oddly enough both my and Terry's research, although performed separately, ended up at the same source. Bennie Fulps at HESCO. HESCO is probably best known for their supercharger for the 4.0, but they also offer other performance products for the 4.0. This said, now is probably the best point to split to our dual builds. I will only add that my other main source of information and design help came from Bill at Custom Jeep of Dallas. Bill is an ex-Chrysler engineer and consummate Jeep builder. I have seen some really wild stuff come out of his shop. He will put just about anything in any Jeep. Right now he has a CJ sitting in his shop with a 454 stuffed in it, and a Willis wagon with a new 4.0 installed. I even saw a 6 wheel CJ he built for a customer. He has been my sounding board, along with Terry and Bennie on this part of the project.

The Plan's

Although my and Terry's project plans are very simular, I belived it would be best to present them seperately. This will give you the chance to get two views of how to approach, plan for and execute a build. It will also cut the size of this page considerably, so that it is should be easier to load and browse. Additionally, to make it easier for us to keep these seperate, even though it may actually be accurate, I have labeled my project "Project 4.5" and Terry's "Project 4.7". So, without further adue;