The Making of a Cummins 6.7-liter Diesel Engine

A Tour of Cummins’ Midrange Engine Plant
By G.R. Whale for

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.


awesome!! oh yeah FIRST!!!

I'm sure everyone will be wondering what that new engine is.
My guess is it's going to be a V8.

How old are those castings for that block?

What hat was the front cover tech wearing?

A Caterpillar hat? Lol!

Is it a coincidence that PUTC is testing HD's and then posts a story on how the Cummins engine is made?

The upset winner of the 2011 HD shootout?

This is interesting -

Baby Cummins for the 1/2 ton?????????

Baseball cap - I'd guess Caterpillar as well.

For the Duramax and Powerstroke guys , If it needs more than six cylinders to be done it does not need to be done , the Cummins is a sweet engine .

Where is the 6.7L block cast? If not in the USA, then where?

What's so sweet about it? Upset winner? I highly doubt it and I still think it will finish last in the shootout. I am not slamming Dodge or Cummins. Don't have a problem with their new trucks or engines. The old cummins diesels were very loud and you always knew when a Dodge Cummins diesel was in the parking lot, taking off etc.

Sure, 800 foot pounds of torque ties ford for the most amount of torque in the class. 350 horsepower is the least amount of horsepower in the class. To top that off, it's how you get the power to the ground that really matters.

Ford and GM have just as nice or nicer looking factories where they build the powerstroke and the Duramax. I laugh at the pro Dodge people that think the cummins is the best engine ever made and will win this shootout. I guess it could happen but I will be very suprised if the cummins beats either one of the V8 Diesels in the shootout. I guess we will just have to wait until August to see who's the king of the diesels. My money is still on the Duramax and Allison transmission. Either way, I don't think there is a bad choice in the class. They are all very capable diesels and great trucks.

Ok, that was fricken cool.

shipped to mexico. LOL

I heard that the GM Sierra had a bad day at the shootout.

True or false?

People in the semi world know that a Cummins is not so great of an engine, but hey, for light duty pickups, it's okay, but still not the best choice.

Very cool post, Mike. Thanks. It gives me heart that some American workers still build a damn fine product.


I would rather have the truck built in mexico than send 1 cent to the UAW. Damn I love the free market.

"Which One-Ton Truck Will Survive the Heavy-Duty Hurt Locker"

This does not sound like a shoot out to me, this is a winner take all, no second place or third. We'll find out in about two weeks--a guess on my part.

Isn't the 6.7l an option on the ford f-650 and f-750

That must be one sturdy shelving unit that the engines are sitting on in the last picture considering each engine weighs a little over 1000 lbs.

@lou: doubt that, did the build on the the GMC V-6 look where it finished? No, really Mike, thanks for the story!

@Greg we liked the Cummins semis we had. Fine machines. We only have 1 Mack now, Mack motor. 1,240,000 miles and counting. Cummins makes a fine motor though.

does this mean dodge won, if they post on ford and gm engines later this could be a hint of who won

Awesome! I'd guess it'll be a 2013 model year release for the little 4 cylinder half ton diesel. Personally I wish it were slightly more than the 2.8L test vehicle's displacement. Here come the half ton diesels! :)

Those engine storage racks appear to be modular built and interconnecting. Each unit stores 2 engines. Pretty cool.

What are the odds that the "no comment" engine is the 2.8L I4 for Nissan?

I wonder if they're setting up manufacture for a US version of the ISF. The ISF comes in 2.8 and some sort of 3 liter size (I think 3.8 as well). The 3 liter size would be nice in the U.S.

Great story! Thanks G.R. Whale and

About the new engine

A V8 at around 5 -liters with CGI in the block would be a smash-hit

@Kurt your correct. Cummins is building "red engines"2.8 and 3.8 size in a new factory overseen by US Cummins enginers and technicians. These are being built for JAC and Foton Trucks in China. The Licenced cummins engines built by other Chinese producers are called "black engines" and are only for the Chinese market not export like JAC and Foton.


The guys I know with semi's love the Cummins..I know owners of KenWorth's,PeterBilt's,Freightliner's,Western Star's with Cummins and non Cummins,the guys who dont have the Cummins all wanted a Cummins in their next truck !! Usually the Cummins is the premium engine.

Guess its like trucks where I am from people in the Heavy Duty truck world know Cummins is the best Diesel engine by far,and wrapping it up with a Dodge RAM make's it better, so we buy them the most,as in Cananda Dodge RAM is the best selling heavy duty truck,and the 1500's are gaining each day !

My family owns a trucking company. We have Cummins and Catepillar engines. While they are both great engines, I have to say that the Cat has been a longer last engine. 1.3 million miles on a Cat B series engine and it only failed because the o-rings around the sleeves gave out.

awesome article to read mike, really enjoyed the story.

@Michigan Bob - Duramax is made by Isuzu.

Thanks Mike for the nice article as always. I'm a Ford guy but I have lots of respect for the Cummins engine. My father had a '91 2500 Ram and it had over 625K miles on it before it got smashed by a dump truck. The 12v 5.9 version had a mere 195hp but made good torque.


The Duramax diesel engine is produced by DMAX which is a result of a joint venture between Isuzu and General Motors Corporation. It is built in Moraine, Ohio. So to say that General Motors had nothing to do with the design of the Duramax is completely false. This is just an attempt to by ford or dodge lovers to discredit GM and say it had nothing to do with the design of the Duramax engine. They would have you believe that GM just buys the Duramax from Isuzu and that is furthest thing from the truth.

Nice try Jack, but I am not going to let you get away with your total distortion of the truth. What's next Jack, are you going to say GM didn't design the tires on their trucks???

Jack....GM bought out Isuzu last year, was 30% GM owned before that.
100% GM now.

Great engines but they do build bad ones from time to time. Last month while in Indiana, talked to four individuals with blown engines in their Dodges. Three out of four had less then 200,000 miles on them. I felt pretty good having 250,000 miles on my 8.1 gas engine.

We have been told by the GM fanbase that the DMax is so great because it is 10 years old. Therefore the Duramax diesel was made before GM fully owned the company and is still an Isuzu design.

Ford right now is only one to desin, develop and manufacture their own diesel in a clean sheet design.

Ram uses Cummins and GM relies on the old Isuzu design from 10 years ago.

GM's NEXT diesel engine may be a complete GM product if they decide to design it themselves. Until then....

GM doesn't design tires. They spec them and tire manufacturers bid on a production contract to provide tire quantities for a given price.

I recall GM did the same with the 6.6L dmax engine. GM didn't have modern light/med duty diesel engine design know-how and went to Isuzu with the engine specifications. The initial joint venture was 50-50 to manufacture and sell DMAX engines. It's different today (60-40). The 4.5L mini dmax was mostly GM designed for what little worth it's been on the shelf.

GM: 60% Isuzu 40% GM
Ram: 100% Cummins
Ford: 100% Ford

Ford right now is the only one to completely design, develop and manufacture their own design.

Ford is going kick butt in the shoout with their own clean sheet design.

Let it be written. It shall be done!

Hopefully Ford dials in the new diesel engine since it's been awhile since they produced the reliable 7.3L.

@Ken, the 4.5L Duramax wasn't done all by GM. It kind of was, but it was the larger version of the 2.9L V6 that GM produced as a joint venture with Italian manufacturer VM Motori. This engine also has a CGI block with reverse flow heads (something that GM fans think that GM invented, and Ford stole)

Now that CAT isnt making over the road engines anymore Cummins is the best way to go for heavy haul engines.

I think its a good sign that Fords 6.7 has been out almost a year and there havent been any widely reported or wide spread problems. Its still too soon to be sure, i doubt many trucks have 50,000k plus on them, but it looks better than their last two engines.

Ford's 7.3 and other engines were produced by Navistar (International Truck).

Ford's new diesel is the first diesel engine designed and built by Ford.

Censoring posts?

Why Mexico?

And when the 100% built by ford powerjoke doesn't win the shootout then what will ford fanatics excuses be??? All this talk about who builds what and what percentage is all designed to discredit the other guy.

In my humble opinion there isn't a better Diesel and Transmission combination in the business than the Durmax mated to the Allsion transmission.

I think all the new diesels and heavy duty trucks are all very capable and they will far exceed what the diesel engines of just 10 years ago. There is no longer a bad choice and the manufactures had to step up there game and meet the new emission standards. Good thing we have choices and not everyone drives the same thing.

The "excuse" if Ford loses will be 99.9% of travel is at a normal elevation. Ford does best at normal elevations so they have 99.9% of the US covered. The .1% that is at 9,000 to 11,000 GM can claim a moral victory for. Ford gets better fuel economy towing.

@David, When ford loses the shootout and it will lose the shootout, it will be at varying levels of elevation. Not just up a mountain so what will be your excuse when ford loses on normal elevation or should I say at sea level? is going to run the trucks at different elevations and ford will lose on all of them. Now what David?

Allison doesn't build the tranny.. gm still does.. and the fastest duramax runs a dodge 48re auto.

I'm excited to see how well the Ram does in the shootout.. I think it will do great in the hills and high elevation.

We'll see.

In the 2010 HD Shootout, at normal elevation, Ford won the 6% grade test with the Job #1 truck.

The Job #3 trucks were never tested at normal elevation.

Davis Dam is at normal to mid elevation and is a 5% average grade.

I think Ford will win Davis Dam. GM will win the Rockies. Ram will win nothing.

Yes, interesting in 2010 how GM had better unloaded fuel economy vs Ford and Ford had better towing fuel economy versus GM. Maybe because Ford didn't quite shine in the tow dept vs GM?

My 04.5 Cummins 2500 loves hills.. just saying..

@Jon and Ford Bob, thank you for the details. Michigan Bob and company readup.

GM diesel: Isuzu motor, Alison tranny, GM frame...
Nonetheless very good setup.

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