Curbside Classic: The Cat 797 Mining Truck – I’ll See Your V12 and Raise You Twelve

Paul’s post on the GM “Twin Six” was fascinating to me.  While I’m sure I’ve seen mention of these, I really wasn’t aware of them in any detail and his brief overview expanded my awareness to yet another GM innovation that for one reason or another never really caught on.

That got me thinking about another engine manufacturer that created a powerplant by marrying a pair of its existing engines in order to fit a specific application. In 1998, Caterpillar introduced the largest “off highway” mining truck the world had seen to that point–the 797–which was powered by mating two V12 Cat 3512 HD engines together to create the 7,147 cubic inch V24 3524B HD quad-turbo intercooled diesel engine, capable of around 3,550 HP and 12,000 lb.-ft. of torque at an easy-going 1,750 rpm. Fuel economy is a bit less than a Prius (or even the Peterbilt 218 Paul recently posted) at 0.3 mpg.

The 797 was unique in that Caterpillar decided to stay with a fully mechanical drivetrain as opposed to the diesel-electric drivetrains more common on trucks of that size. It has a seven-speed planetary gear transmission, all controlled by numerous on-board computers. The truck itself was also the first to be completely designed on computer.

The current 797F model, introduced in 2008, is powered by a Cat 175-20 twenty cylinder engine (single block) of 175 Liter displacement, which is rated at 4,000 HP. This enables the truck to carry a load of about 400 short tons (equivalent to about 120 Ford Excursions) at a top speed of around 42 mph (loaded). With a 44/56 weight distribution, a gross weight of well over a million pounds and a live rear axle, you won’t be running it through the slaloms. 0-30 times of about 27 seconds won’t win any points at the drag strip, either.

It’s hard to comprehend the scale of these trucks. For example, you’ll need a really big “four-way” wrench to change a tire on the 797. Each 12′-10″ tall wheel is attached by 47 lug nuts, each torqued to 2,300 lb.-ft. Six Michelin tires are required per truck and they’re the largest tires made on the planet–59/80R63 is the size if you need to order a set at Sam’s, and they’ll run you about $42,500 each (as of 2009).

The 3524B (and current C-175-20) engines are manufactured at Caterpillar’s Lafayette, Indiana engine plant and then shipped via flatbed semi to Decatur, Illinois for installation in the frame. The final assembly of the 797 is done at or near the customer’s site, and requires numerous semi loads to deliver. A team of seven mechanics will spend about twenty days working 24-7 to weld the dump body together and assemble the truck.

A new 797F will run you about $5,000,000, and can be completely rebuilt several times over its typical twenty year life. I was in Canada a few years ago at an Oil Sands mining site, which had about 100 trucks in operation at that time. Except for maintenance, these trucks are kept running 24/7 (time = money), and if you shut one down outside the shop in the winter, you’re not going to get it started again until spring!

To my knowledge, no-one has ever wrapped a beautifully streamlined aluminum body around the 3524B engine (Jay Leno, call your office!). But if you’re one of those “Men Who Has Everything And Just Needs Something to Carry It In,” I suspect the 797 will fit the bill perfectly.