Introduction:

1989,1999 by Hib Halverson, all rights reserved, no use without permission.

Amazingly, Chevrolet, which has produced tens of millions of rather low specific-output, (there were exceptions-consult your Red Bow-Tie encyclopedia under ZL1, LT1 or L88) cast iron, pushrod engines, suddenly gives us LT5: a design that was Formula 1 state-of-art only 10 years ago. What's more amazing...no, let's say "revolutionary"...is that while other OE's indeed build production DOHC, aluminum V8s; none have been done in the quantity Chevrolet has planned. Expectedly, the facility where LT5 goes together is a departure from the norm. Last December, when we toured the LT5 line at Mercury Marine's factory in Stillwater, Oklahoma, we...

"What!?" reader exclaims.

"Wait just a damn minute...Mercury Marine?"

But, it's true, it's true! At face value, this is almost humorous: a manufacturer that most identify with outboard motors building the most advanced production automobile engine this country has ever seen. Examined closely, however, one concludes Chevrolet/Mercury Marine is an excellent match.

Besides making outboards, Mercury Marine ,or "Mercruiser," as some say, is the largest maker of gasoline-burning marine powerplants for inboard and stern-drive (inboard/outboard) applications. Its V6s and V8s are based on Chevrolet engines. For years, a special division has built versions of these units for boat racing and other marine applications demanding very high, but very reliable power levels. Fact one: Mercury Marine builds high performance V8 engines in the quantities required by the Corvette ZR1 program and has an existing relationship with Chevrolet. Mercruiser's stern drives use die-cast aluminum parts and it builds a 3.7-liter four-cylinder that uses an aluminum cylinder block, one of the larger die-castings in the industry. Fact two: Mercury Marine is the world leader in the production of die-cast and other types of aluminum engine parts.

It follows that Chevrolet's exhaustive search for an organization suitable to build LT5 would lead them to the Mercury Marine division of the Brunswick Corporation in Stillwater, Oklahoma. Now, back to our story.

...could see this was no dingy engine plant. It was squeaky clean-with even cans labeled "LT5 Trash", destined for an LT5 landfill, perhaps? There was bright lighting, a low noise level and enthusiastic people serious about making engines. The 21,000 square-feet devoted to this task at Stillwater are divided into two parts: the machining area and the assembly line.

Upon entering the machining area, machinists will think they'd died and gone to heaven. All equipment is new and most is of the computer-numeric control (CNC) variety making for accelerated production rates and precise quality control (QC). The entire LT5 machining operation would take many pages to cover so we'll look at the craftsmanship in cylinder case and main bearing girdle. These parts form the LT5 bare block, are serialized during machining and are treated as a unit thereafter.

Most block work is done in Cincinnati Milacron T10 Manufacturing Cells. These are highly sophisticated, automated, CNC mills that automatically change their own tools. These units take the two raw castings and (take a deep breath) drill all bolt and dowel holes; bore the cylinder liner locations (with tooling that both surfaces the head decks and does the liner locations holding a depth tolerance of .0007 in....amazing!); cut all flat surfaces on both parts and drill all oil passages.

A separate machine line bores the main bearing locations. A straddle mill cuts the inside of the block for crankshaft counterweight clearance. That unit is equipped with polycrystalline-diamond cutting tools allowing a 6000 feet-per-minute feed rate…the operator had better pay attention because the work's speed across the mill can exceed 60 miles an hour. They don't take prisoners at this "machine shop", you see.

All this takes about 45 min. per set and is an incredibly precise activity. The line boring is done with diametrical accuracy of .0004 in.…that's four ten thousandths of an inch...astonishing when you consider the operation bores two dissimilar metals and is done in an automated, volume-based environment. The Manufacturing Cells' axis positioning accuracy (how precisely they place parts prior to each individual machining step) is .0004 in. within a cube 26 inches on a side. Each individual machining step repeats within .0001 in. Repeatability is a measurement of how accurately each machining step is completed on a continuing, per unit basis. The rest of LT5's aluminum pieces are finished with the same accuracy and efficiency. To keep track of all these teeny-weenie dimensions, Mercury Marine uses quite an array of QC procedures and equipment. It starts in the Metrology (science of measuring) Department. In this special temperature and humidity controlled area are two bench-mounted digital micrometers accurate to .000001 in. (1/1,000,000 in.) along with other specialized metrology equipment.All other micrometers, gages, torque wrenches and any other measuring devices used in LT5 production are periodically checked on this equipment.

On a regular basis, finished parts, primarily blocks or heads, are bolted on a Cordax RS50DCC direct-controlled coordinate measuring machine. Looking like something from the Star Wars prototype shop, it has a six-foot-square steel platform about two-feet above the floor. A "gantry" that traverses the platform holds a robotic arm that can move vertically. At the arm's end is a probe that rotates 360° horizontally and moves in a vertical arc of 105°. These movements allow the probe to reach any point on the part to be checked. The three-dimensional location of each point contacted by the probe is fed to a computer and compared to a "perfect model" stored in the computer's memory. In 45 minutes, the Cordax checks (or "qualifies" as machinists say) every dimension specified for inspection, 823 data points for a block. Done by hand, the task takes 60 man-hours.

Precision? You bet! Cordax accuracy on a single axis is .00015 in. and in three dimensions, within a cube of 30x40x48 in., is .0005 in. The machine automatically changes probes and sits on a "Barry Mount Vibration Isolation System" that is so stout, you can drop a cylinder block (an iron one, yet) on the floor next to the machine and the qualification process is unaffected. Don't think you get Cordax accuracy at K-Mart. The RS50DCC costs a cool quarter-million bucks. Quality control devices aren't limited to mic's and DCC machines, either. There are: real-time X-ray/video inspection units, fiber-optic borescopes, chemical and spectrographic analysis, stroboscopic engine balancing, fluorescent-dye leakage detection all backed by sharp-eyed workers who want each LT5 to be nothing short of excellent.

All this is only marginally effective without statistical process control (SPC) to tie it all together. Joe Carroll, General Manager for Quality Control at Mercury Marine, Stillwater, defined SPC as "...using statistics generated by the process to control the process and ensure its stability."

Every LT5 machining operation and quality control activity generates data that is fed to Stillwater's central SPC computer which produces comprehensive information used to monitor quality on a piece-by-piece basis. SPC detects unacceptable quality trends and helps Mercury Marine to solve problems before they have an effect on the process. This description is a bit simplistic for space reasons but there is no denying SPC's value. At the time of our tour, Mercruiser's LT5 operation had an average QC envelope 70% the size of the allowable tolerance. This means that although the main bearing bore diameter tolerance is .0004, in practice, Mercury Marine is holding it within .00028 in. Joe Carroll stated that Mercury Marine's goal with SPC is 30% of the allowable tolerance within six months of production start up.

LT5 assembly is a work station system and was operating under prototype conditions (one engine per day) during our visit. It will be capable of 25 units daily but initial demand will be less than that. The first two stations assemble the short block. The next few sub-assemble the heads. At mid-line, heads, valve train and cam covers are added to the engine. The last stations install ignition hardware, starter, alternator, induction system and other accessories. Then, the engine is hooked to a computer terminal where any electrical anomalies are instantly pinpointed. The final step in Mercury Marine's QC program occurs next: a 14 minute dynamometer test consisting of initial fire-up and break-in schedules followed by a full-throttle run to verify that each LT5 generates its rated power.

The most blatant difference between LT5 assembly and that of other U.S. engines is that excepting some cylinder head and engine balancing tasks; LT5 is done entirely by hand…like any racing engine should be. Consequently, people are more important to the success of the project than fancy machines or trick QC procedure.

Mercury Marine's LT5 workers are young and enthusiastic. Average age is 28.5 years, a phenomenal statistic considering at most engine plants that figure would be the average length of service! Forty-percent are women and a high percentage of the work force is college educated. That level of schooling is unusual in automotive assembly work and is due to the proximity of Oklahoma State University which also calls Stillwater home.

At Mercury Marine, you don't just lay your union card on the Personnel Director and say, "Hey, dude, like–ah–I wanna work on LT5s, okay." First off, there's no union and LT5 jobs go to folks with more smarts than has our imaginary applicant. Virtually all spots on the LT5 line are prestige items and go to people who already work at Stillwater. We met one worker who so badly craved an LT5 assembly slot, he took a two-fold drop in job title and a corresponding pay reduction to get it. Here's a bit more on a couple of the LT5'ers.

Linda Ousley assembles the intake plenum unit, installs it on the engine, attaches the throttle body assembly, torques all fasteners to specification then makes all associated hose and wire connections. This attractive, black-haired lady is in her late-20s, has been at Mercury Marine almost nine years and is one of many pleasant assembly folks we met. At the time of our visit, she'd been on project for two-weeks. Prior to that she worked the marine V6/V8 line. She described the prevailing assembly line attitude to us: "I'm proud to work on the motor," Linda said with emphasis such that, to her, LT5 is not just "a motor" but "The Motor."

Bill Kepple is one of two people doing the LT5 lower end. He installs the liners into the block, arguably the most critical job on the line. He assembles the rod/piston/ring units and installs them, too. Bill does this with all the care you'd see in any premium race engine facility. Bill, who's in his late-30s and has worked for Mercury Marine for 5 1/2 years, is a LT5 veteran having started on the project in February, 1988. Previous to that, he worked on the line that builds Mercury Marine's 3.7-liter four. Like Linda Ousley, he views his job as a choice occupation.

Qualifications and experience at Stillwater are the main factors determining whether or not one gets into this special department. Then, applicants must either have completed or be willing to take 40 hours of statistical process control classes. Those applying for positions in the machining side must also take an 80 hour CNC course. Everyone working the line must crosstrain for all other assembly tasks. In the words of Jim Cunningham, Mercury Marine's Project Manager for LT5, "...that way, every worker will be able to build the engine." This promotes knowledge of the product and of how individual assembly line operations interface with each other.

All should now understand why Chevrolet chose Mercury Marine to build the LT5 but what about why Chevrolet did not assemble the engine in-house. Even though innovation and quality in the American automobile industry have increased greatly of late, General Motors is a large bureaucracy that's somewhat inflexible and resistant to rapid change. It was known within the Corvette Group from the beginning of King-of-the-Hill that the engine, to be a success, would have to develop quickly and would require some schools of thought unobtainable within GM. As a subcontractor program, the manufacture of the LT5 has operated with certain philosophies, operating methods and fiscal procedures beyond the control of the crusading bean counters in Detroit. Terry Deer, Mercury Marine's Senior Buyer for LT5, tells us that when time came to line up vendors, Chevrolet instructed him to, "Go where you have to and find the best. We want a world class engine so find world class suppliers." Of course, the best pieces cost top dollar. To date, those running the King-block effort at Stillwater say that the Red Bow-tie guys have been more than willing to write the checks. How often have we seen that from an American OE? So, next time someone says that Mercury Marine builds nice little boat motors; tell them about LT5.