Fieldside Classic: Hesston 6400 Windrower – The Slant Six Dons Work Clothes

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The old saying “Make hay while the sun shines” simply means taking advantage of good conditions to ensure a quality harvest. It only takes a little rain to reduce the feed value of hay, so one keeps a sharp eye on the weather forecast before cutting. Here in the Middle West, it takes from 2-5 days of dry weather to properly cure the hay before baling. To improve my haying capabilities, I purchased a (very) used Hesston 6400 Windrower a couple of years ago. It replaced an ancient and finicky sickle-bar mower, and I was pleasantly surprised to find it powered by the venerable Chrysler Slant Six industrial engine…

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The Chrysler Slant Six had its genesis along with the development of the 1960 Plymouth Valiant when, in 1957, Project A901 was initiated. The project’s aim was the development of a compact car to battle imports that were starting to gain traction in the U.S. auto market. Internally, the car was called ‘Falcon’ (until Ford introduced their car by the same name), and the early engineering direction for its layout involved using a rear-mounted, four-cylinder engine tilted to fit below the rear parcel shelf. The four proved to lack low-end torque, which led to the addition of two cylinders to produce the familiar configuration we know today. When word leaked that Chevrolet had rolled a Corvair in early testing, Chrysler abandoned the rear-engine configuration altogether and returned to a traditional front-engine, rear-drive setup.

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Willem Weertman was the principal designer of the Slant Six, and in an interview with allpar.com, he indicated that the engine was essentially a clean-sheet design that owed little to the previous L-head Chrysler sixes that had been in production since 1929. Chrysler flatheads were last used in automotive applications in 1959 Plymouth and Dodge cars, and in 1968 Dodge M37 military trucks. Production for industrial engine applications continued as late as 1972.

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What made these old engines so desirable for so long was their incredible low-end torque. The 265.5 cu. in. (4.35-liters) six used in cars made 218 ft/lbs of torque at only 1,600 rpm—which made it ideal for industrial uses. By the late-’50s, the L-heads, which were available in a range of displacements up to 413 cu.in. (6.77-liters), were considered thoroughly obsolete. As Weertman and his engineering team worked on a new-overhead valve engine design, he noted, “Making it an extremely compact and lightweight six gave us plenty of challenges, and we were pleased with the way it came out.”

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Tilting the engine 30 degrees in order to fit under the Valiant’s hood provided the opportunity to use longer and more efficient intake and exhaust runners, as well as the happy side benefit of better access to engine accessories, including even those on the underside of the engine. It also moved the center of gravity a bit lower, which helps improve vehicle handling.

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The Slant Six would prove to be a very versatile and durable engine platform, one that responded enthusiastically to such performance upgrades as the Hyperpak setup (seen above) that made 196 hp. The current Bonneville speed record for a Slant Six, set in 1965, stands at a shade over 142 mph. Aluminum-block versions were produced from 1961-1963, and prototype turbo and diesel variants were developed as well. At the other end of the spectrum, tuned for economy in a light car like the 1976 Plymouth “Feather Duster,” the Slant Six could deliver up to 30 mpg on the highway. These engines have been known to run 500,000 miles or more before needing an overhaul. Weertman clearly knocked it out of the park with the Slant Six, and later he’d repeat that success with the development of the 3.3-liter V6 introduced in 1990.

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But enough about development history. Due to the engine’s fat torque curve, it was only natural for Chrysler to “make hay” and offer the new Slant Six for use in any number of industrial, truck and marine applications. Heavy-duty engines typically had a forged crank, double-row timing chain and chrome plated upper piston rings. Depending on their application, industrial engines might also have had polyacrylic valve stem seals, positive valve rotators, stellite-faced exhaust valves and a high-volume oil pump.

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We’ve already covered the Cortez motorhome, and the following are a few other examples of non-automotive Slant Six applications:

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How about a nice, tidy marine installation?

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Or a clean-looking electric power generator set?

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A Slant Six has been faithfully driving this pump for a number of years.

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Many an aircraft tug was powered by the engine…

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And it also found a happy home in various forklifts.

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And finally, the engine’s durability and power properties made it a natural for ag applications. Hesston is well known for haying equipment, and produced the 6400 from the late 1960s through the early 1980s. (Mine is mid-late 1970s vintage.) Essentially, the tractor is a super-sized zero-turn mower. The Slant Six drives two hydraulic pumps through a series of sheaves and belts while the main drive wheels do all the moving and turning—the rear wheels are free-castoring.

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The business end of the Hesston has a large takeup reel that rotates to sweep the hay into the cutter bar. This oscillating bar has numerous knives, or sickle sections–triangular, serrated blades working against fixed guards to cut the hay (or any critters that don’t move away fast enough—I occasionally find portions of snakes, frogs and other field animals poking out of hay bales). The belt drive allows for some give in the system in case you hit a rock or other obstacle.

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Here’s the view from the driver’s seat. The cutting head is 10′-5″ wide (3.2m), and an auger pulls the cut hay into the center of the machine where hard rubber rollers crush (‘condition’) the hay before dropping it out the back into windrows. The crushed stems of the plants lets them dry out (cure) faster, which can shave one or two days off the drying time versus non-conditioned hay.

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Unfortunately, the Hesston’s controls are somewhat “user hostile”. Pushing the steering wheel forward or backward produces the movement you’d expect. Turning the wheel steers the tractor by altering the relative speed and direction of the drive wheels, which makes the unit highly maneuverable. This works pretty well, until you try it while backing up—everything then goes backward from what you expect! I’ve come very close to putting the back end through the barn wall more than once.

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And speaking of the back end, let’s have a closer look at that Slant Six… Yep, as is typical, the exhaust manifold is cracked, and the previous owner “farmerized” a quick field repair it both it and the rotted out exhaust pipe (which I have since replaced). Given that I hay only about 12 acres, the engine accumulates a mere 20-25 hours of running time annually. At that rate, I suspect it won’t need an overhaul for at least another decade.

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Well, it looks like now the hay is cured, and doesn’t even need raking! Time to go bale. Anyone want to help?