The Making of a Cummins 6.7-liter Diesel Engine


Cummins builds diesel engines well beyond 70 liters, so anything below the Class 5 truck market is “light duty” to them. However, the current High Output and standard 6.7-liter ISB inline-six oil burners in Ram’s 2500/3500 heavy-duty pickups and 3500/4500/5500 chassis cabs are built to medium-duty specifications. They’re made at the Columbus Midrange Engine Plant (CMEP) just south of Cummins’ world headquarters in Columbus, Ind. We stopped by to see where this popular truck engine is built.

CMEP was built on more than 400 acres in 1971, and it originally built components such as pistons, connecting rods, pulleys, rocker housings and water pumps. It closed in 1988 to convert to engine production and reopened in 1991, and it has fed Dodge/Ram assembly lines ever since. CMEP has supplied other chassis manufacturers, but that production pales in comparison with the Dodge numbers, and the plant should build engine No. 2 million sometime soon. Total manufacturing and office space totals 587,904 square feet.

Located just off Interstate 65, CMEP is easy to find by road or even by air. The red expanse is the plant’s roof, which doubles as the 500-space parking lot. Since the roof expands and contracts up to 16 inches in temperature extremes, sealing it is a regular maintenance item.

1. When the 6.7 engine block arrives on the assembly side of the building, the freeze plugs and cam bearings are already installed.

This is the closest assembly plant to Cummins HQ, though there is a facility in Columbus that machines heavy-duty blocks and heads and will machine and assemble a new engine currently under development. A polite “no comment” regarding what that engine is.

During our visit, the plant was building about 420 6.7 engines a day on a full-speed first shift and a quarter-speed third shift. The plant can produce substantially more; in 2004, it built 167,622 engines.

CMEP employs about 520 people, most of them on the plant floor and the remainder in the cubes and glass offices. There’s a central courtyard, and from virtually anywhere inside — including from the paint booth — you can see out to the lawns or woods. Occasionally, a wild turkey or deer will scamper by.

The plant has the usual array of loading docks, lube tanks, cafeteria and an auditorium of glass on four sides. In one sizable glass enclosure is a server bank glittering like a chunk of lava, just like the WOPR computer from the movie “WarGames.”

2. The block is flipped onto a cart for bottom-end installation. Lifts are handy for 140-pound cranks.

Line employees rotate every hour, and everyone we saw wore a pedometer. Pass a certain threshold, and it’s good for a health-insurance discount the following year. The recreation area is less than 15 minutes away, and there’s even an employee-volunteer straw-bale garden that delivered more than 500 pounds of produce to local charities last year.

Engine production begins north of the central courtyard with machining activities on the block line. Our visit coincided with a large group of enthusiasts from the Turbo Diesel register, so we didn’t see it this time, but have in the past. Apart from the windows, it’s similar to other block machining facilities.

3. Camshafts are installed carefully by hand. With the engine inverted, you don’t have to secure the lifters.

4. This bank of robots fits rings and joins connecting rods to pistons.

5. A short block complete with seals, front plate and noise reduction.

6. The cylinder head with integrated minimal intake manifold is lifted into place. That makes it easier on the employees, and the head bolts never fall out.

7. We won’t tell you what kind of hat the front cover tech was wearing, only that we waited for him to take it off.

8. The red cast on this engine is not from a test. It’s the barcode reader for the injectors.

9. After the remaining valve train is installed, the wiring harness is next.

10. Along with the variable geometry turbocharger, output and emissions, the size of wiring harness represents the biggest change from the first BT5.9 engines. Other components such as the turbo and filter housing (not pictured) are plugged in as needed.

10A. The exhaust manifold, EGR and turbocharger are assembled separately, then joined to the engine.

11. This complete engine is en route from testing to painting. Each engine is started and briefly run (with fuel and oil, without coolant). There are myriad checkpoints along the line, and if an engine doesn’t pass one of them, it is pulled, sent to repair, set to spec, and then it rejoins the line.

12. Although the block arrives at assembly finished, the complete engine is masked off for the paint booth, where a sealer is applied.

13. This is not blue paint; it’s merely a coating formulated so it looks blue while it’s wet.

14. The drying oven. Note the blue has disappeared, and the engine appears clear-coated now.

15. We don’t know if management told everyone to be happy, but like everyone else, this post-paint team looks pleased.

16. From CMEP, the engines are trucked to Chicago, then loaded on trains bound for the Saltillo Ram assembly plant in Mexico.


Latest expert reviews