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Mopar Engine Rebuild - The Small-Block Mopar Part I

Posted in How To on February 6, 2007 Comment (0)
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Photographers: Tim Jenkins

Project Grand Caddy has been around for well over two years now and has been a great daily driver and mild trail vehicle. Last June, the ZJ took a turn for the worse: It found itself a nice little hole in a river along the bank. Needless to say, the engine hydro-locked and bent the number eight rod.

The vehicle up until that point had been very dependable, even though the engine's odometer read 166,000. The motor was strong, offering plenty of power and torque with a slight push of the accelerator pedal. It didn't burn oil, nor did it smoke. The aforementioned unfortunate incident gave us the opportunity to play with one of our favorite contraptions, a well-rebuilt Mopar 5.2L Magnum small-block (318 ci).

The Mopar small-block has been around for a very long time. In 1964, it started life as a 273ci Mopar LA engine. Production of this engine lasted until 1992. The newer Magnum 5.2L small-block is basically an updated version of the LA engine and was produced from 1992 to 2001. A 5.9L version of the Magnum engine was produced from 1993 to 2003. The two share similar parts: In most cases, what fits on the LA engine will more than likely fit on the Magnum engine. Both Magnum engines found their way into the Jeep Grand Cherokee ZJ.

Unfortunately, we just don't have room in the magazine to give you a complete, step-by-step build of the engine. Instead, we will highlight the engine's high-quality Clevite components, performance options, important steps in the build process, and why the engine was built the way it was. If you're looking for complete, in-depth, small-block Mopar building, we highly recommend How to Rebuild Your Mopar Magnum V8 as reviewed in this month's Media Review department.

There are three companies that played a very important role in the build of this engine. Tim Jenkins at DOA Racing has been building top-shelf performance and race engines for many, many years. Tim directed all the machining and built the engine - we have the highest regard for Tim's engine-building abilities. Clevite Engine Parts is one of the world's largest manufacturers of engine parts. Clevite supplied some of the finest engine components available for this build. Don-A-Vee Chrysler and Jeep in Placentia, California, completed the installation of the new engine. Don-A-Vee has not only been selling Jeeps for the last 25 years, the company has been instrumental in Jeep enthusiast development. The dealership originally forged ahead to be one of the first in completing performance engine swaps on Jeep vehicles and has worked closely with Chrysler on Jeep development.

It would have been very easy to go all out and build our Grand's engine with the performance of a fighter jet (joke). The Mopar small-blocks are an excellent base to build a high-performance engine with 800-plus horsepower. Right off the bat, the engine is a little larger than most other small-blocks. The dimensions of the engine's crankcase offer more room for modifications. The block is a perfect match for stroker performance kits.

This vehicle is driven on a daily basis and used for extended travel, so gas mileage was a major factor in the build. The Grand Cherokee doesn't get that great of mileage as it is, so any performance modifications, such as a souped-up cam and higher compression, would have reduced fuel economy even more.

Tim found us a good, low-mileage engine core for a great price. The engine was thoroughly cleaned and then shipped off to the machine shop. Tim is one of the most knowledgeable engine builders we know. If you are serious about having your Jeep engine built properly, he is available for 4.0L straight-six and Mopar V-8 builds.We turned to Clevite Engine Parts for all internal components and received top-of-the-line Clevite engine bearings, Perfect Circle piston rings, and Victor Reinz gaskets. We spoke with Director of Brand Development Bill McKnight who educated us on a lot of the research and development behind Clevite performance parts.

We explained that we wanted to complete a straight-up engine rebuild on our Grand Cherokee - we didn't want a high-performance gas guzzler. We wanted dependable, long-lasting parts able to withstand harsh driving conditions. What we received were a new roller cam and lifters, a high-volume oil pump, and all of the other parts, including pistons, timing chain and gears, and freeze plugs. All of these are high-end O.E. replacement parts. Clevite offers just about all engine components for domestic and foreign vehicles. Another thing that makes these components so attractive is the fact that none of them is made in China.

Bill took some time to point out some interesting features and considerations of particular importance to anyone wanting to boost performance or enhance durability during the rebuilding process.

For instance, the connecting rod bearings we received were Clevite's recently introduced TriArmor design, which incorporates an exclusive moly-graphite coating on top of a complete, otherwise-unmodified, Clevite 77 performance bearing. This coating is just 3/10,000 inch thick and comes out of Clevite's engine development program meeting the highest levels of performance demanded by NASCAR and other racing circuits. It is now offered for popular domestic and import engines. The specially coated bearings play an important role where the reciprocating action places the highest stresses on the bearings and crank journals, but also where main bearings' stresses tend to be particularly high.

This coating adds several benefits to Clevite's performance bearings. The exclusive moly-graphite coating is a super-slippery, state-of-the-art material that provides three key benefits. First, it offers protection to both the bearing and the crankshaft journal, especially during cold start-up when the protective film of oil has not fully developed. Second, with its greatly reduced coefficient of friction, this coating contributes to increased power and fuel efficiency. And finally, when this coating wears off after many miles of service, there's still a complete, unmodified, premium high-performance Clevite bearing underneath, ready to begin service all over again well into the new life of the rebuilt engine.

Machinists and engine builders will probably be asking, "But what about clearances to accommodate the added thickness of the coating?"

We were told that "with the coating just 3/10,000 inch thick on each bearing shell, the total reduction in assembled bearing diameter is 6/10,000 inch - 3/10,000 inch for each shell. At just over half a thousandth, this variance will often allow bearing clearances to stay within allowable tolerances."

However, for the engine builder who is obsessive about clearances, Clevite offers bearings for many engines in -0.0005 inch (half a thousandth extra clearance) so he can mix and match bearing shells to achieve the precise clearance he needs.

We also learned quite a bit more than we thought about piston rings. Compression rings were made of plain gray cast iron; however, engineers at Perfect Circle soon learned some pretty interesting things about the ring pack in automotive engines. One revelation was the fact that piston rings typically account for about half of all of the friction in an internal combustion engine, so rings have a major effect on the power and efficiency of an engine. Another was the fact that modern top rings often see temperatures close to 4,000 degrees F. Both these conditions indicate the need for a moly-coated top compression ring in a modern engine.

Clevite's engineers have also learned an even more revealing piece of information regarding piston ring performance. Typically, pistons have three rings - two top "compression" rings and a third, usually multipiece, "oil" ring. Through sophisticated testing, it was discovered that the roles of these three rings are not what they were previously thought to be. They learned that 90 percent of the role of the top ring is compression control, with 10 percent being oil control, and these percentages are reversed for the third, oil control ring.

As for ring design, many factors come into play. Ring coatings, base material (gray iron, ductile iron, or steel, for example), bevels, twist, clearances, even oil ring design, all contribute to performance and efficiency in many different types of engines. And remember, in an engine running at 6,000 rpm, each cylinder is seeing a combustion event 50 times a second! So, ring design is a very precise science and must be exactly right for a particular engine family.

Head gaskets are extremely critical in engine building and can vary in design and function. Many factors come into play in determining the optimum head gasket design for a given engine. Head and block materials, compression ratios, sealing widths, surface finishes, and even combustion chamber shape can play a role in the demands placed on head gaskets. We received Victor Reinz Nitroseal graphite-type head gaskets. This type of gasket consists of Teflon-coated graphite clinched to a perforated steel core with a stainless steel flange. The stainless steel flange resists damage from combustion gases and pressures, and the graphite facing results in more efficient heat dissipation in order to reduce the amount of heat transferred to the combustion seal.

In the next issue of 4WD&SU, we will discuss machining, balancing, and head porting, as well as tell you about some of the more important points of fine engine building.

Sources

DOA Racing
Mooresville, NC 28117
704-799-6261
http://www.doaracingengines.com

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