Rave Review for Komatsu's D51

Sept. 28, 2010

When Jim Schultheis shows up on a jobsite, chances are that the superintendent will shift people and machines around to get him on a grading tractor. After 40 years as a professional operator, he can competently run any machine you give him, but his reputation on a finishing dozer usually precedes him to the site.

"It must be in the genes," he says, "considering that both my father and uncle were finish hands."

Schultheis spends the construction season working as an operator, but spends the off-season as an instructor at the 125-acre training facility that Local 649 (International Union of Operating Engineers) maintains near Mapleton, Ill. (just west of Peoria). So when we asked Local 649's training director, John Salzer, if we could bring a new Komatsu D51PX-22 to the site and borrow an instructor for a Hands-On-Earthmoving evaluation, Schultheis drew the straw.

Komatsu's product manager for crawler dozers, Armando Najera, arranged to have the D51 shipped from Komatsu's Cartersville, Ga., demonstration facility. And on an unseasonably warm morning in late May, the Construction Equipment crew met up with Schultheis, Najera, and Komatsu product marketing manager, Bruce Boebel, for the evaluation.

D51 walk-around

First thing, Najera and Boebel gave us a tour of the new D51PX-22, which has a ready-to-work weight of 28,880 pounds and is the low-ground-pressure counterpart of the standard-track D51EX-22. These recently introduced 130-horsepower (net) machines, featuring a new Komatsu dual-path hydrostatic-drive system, are replacements for the D41P-6C and D41E-6C, which were rated at 110 net horsepower and used a Komatsu three-speed, planetary-type, powershift transmission.

"The D51 is designed to be very nimble and final-grading focused," said Najera, "but with the power and blade capacity to move dirt fast. You're not going to clear a shopping-mall site with this tractor, but you can still push a lot of dirt — and it might save bringing in a larger dozer on some sites."

The fresh engineering in the D51 makes it a considerably different tractor than either its D41 predecessor or its smaller hydrostatic-drive counterparts in the Komatsu line. For example, unlike the rigidly mounted undercarriages used on these machines, the D51 has oscillating track frames, employing an equalizer bar and pivot shafts, which are mounted forward of the final drives and absorb shock loads.

"Some users are of the opinion that oscillating track frames make grading more difficult," said Najera, "but Komatsu's extensive testing has shown little difference, compared to a rigid undercarriage."

Track assemblies for both D51 models (PX and EX) are identical, with seven rollers and 9 feet of track-on-ground. The only differences are track gauge (74 inches for the PX, versus 70 for the EX) and wider shoes (28 inches versus 20). Compared to its D41 predecessor, the new tractor is designed to provide 25 percent more undercarriage life, using thicker sprockets, larger-diameter bushings and longer links.

Since Schultheis had an hour or so on the previous day to get acquainted with the D51, he'd taken note of some of the new tractor's other design features. Among them were the shifted-forward operator's position and the uncommonly good view out the front window.

"This is the only tractor I've been on that lets you see the center of the blade," he said. "Usually, the hood is in the way. A new operator could learn faster on this machine, because of the visibility to the blade."

Najera explained that the operator's station is moved some 20 inches forward on the D51's new mainframe, in order to place it closer to the machine's center of gravity for improved balance. This position improves on the "back-of-the-bus" view afforded by some grading tractors, he said, and gives a more stable ride.

The good view that Schultheis mentioned results primarily from moving the D51's cooling package (radiator, oil cooler, charge-air cooler and fan) to the rear of the machine. With the engine compartment thus devoid of cooling components, the D51's nose can be dropped sharply to reveal more of the blade.

And still on the subject of visibility, Schultheis called our attention to another D51 feature that impressed him.

"The exhaust stack is placed so that the right windshield post hides it. That's good thinking, because you already have a blind spot with the post, so why create another with the stack?"

As we moved around the machine, Schultheis rapped the D51's hood and said that when he checked the machine's fluids upon its arrival, he'd been impressed with the sturdy construction of the hood and service door.

"It's 6-millimeter [1/4-inch] material," said Boebel. "We didn't want the distraction of a vibrating, noisy hood when an operator's concentrating on the grade."

This brought us to the newly designed, 11-foot-wide, six-way (power angle and tilt) blade, which the D51EX also can use as an alternate to its 10-foot-wide version. The new blades for the D51 incorporate added box-section reinforcement for increased strength. The D51 also uses a newly designed, cast-steel, inside-mounted C-frame, which connects to the blade via a bolt-on center ball incorporating a large surface area.

Last stop on the tour was the new cab, where Boebel gave Schultheis a run down on new features. In particular, Schultheis took note of the shape and texture of the joystick controllers — the left for steering and directional control, the right for blade control — saying that they fit his hands well, that they were neither too slick nor too sticky, and that the flare at the bottom of the levers was a natural support for the sides of his hands.

Boebel pointed out that in the left joystick are two buttons for "shifting" the transmission — actually for controlling the volume of oil flow through the hydrostatic system, and thus, regulating ground speed when the electronic throttle is turned up. This two-mode system, controlled by a selector switch on the dash, can program the buttons to increase or decrease ground speed in three distinct shifts, or in 20 seamless increments, the latter providing virtually infinite variation of speed up to the maximum.

In the dirt

In the first exercise with the D51, Schultheis started at the bottom corner of a 200-foot-long, 30-foot high berm of well-compacted sandy clay, then pushed large loads up and across the face in a sweeping arc to the far bottom corner, cutting perhaps 5 inches deep. After a number of such passes, we asked for his thoughts.

"It's got power. It carried a lot of dirt for a finish machine — you can see the good-sized windrow it left. I don't think most grading tractors this size would move as much. I turned with big loads to see if the engine would pull down or the tracks would slip, but neither happened. This is sandy material, and if the tracks are going to slip, they'll do it here."

He also was impressed with the D51's control features:

"I liked the transmission buttons. I preferred the mode that lets you dial in speeds, because you can set the exact speed you want, which was just short of second gear on the indicator for this application. And you don't feel the shifts; it's very smooth. I also liked the detent in the forward/reverse lever. If you have to hold a lever in forward or reverse against spring tension, it's hard on your wrist. Overall, it's a very controllable machine — the steering is smooth, and the blade hydraulics are quick, but that's okay — you just adapt."

In a second exercise, we asked Schultheis to take the D51 into an area where student dozer operators had created a washboard — to get his opinion on how the tractor would handle itself in rough-terrain grading. In two passes, he could transform a swath of ridges and dips into an acceptable grade, but he said he'd make a third pass on a real job site. He commented again on the D51's power and controllability, and noted that the machine provided a good ride in this bumpy material. Then he made an observation that we'd probably never have considered.

"The visibility from the cab is excellent, because whoever designed it realized that the flatter the doors, the better the view. The whole point of a grading tractor is seeing the work in front of you, but if the glass in the doors comes back from the windshield at too sharp an angle, you get a lot of distortion. You'll notice that a lot of finish hands will open the doors when getting close to grade — which defeats the whole idea of the cab to keep things quiet and clean."

We then asked if the set-forward operator's compartment affected his ability to judge the grade.

"I thought at first that it might. But like most operators on finishing tractors, I mostly feel what the machine is doing on the grade by what comes through the seat. This tractor still lets you sense that. A contractor once told me, 'Schultheis, your brains are in your [posterior region].' I said, 'thanks for the compliment.'"

Slot dozing was a third exercise, and the object here was to push as much dirt as possible. The D51's power was again at the top of the list for Schultheis, but he noted a couple of creature comforts as well.

"It impressed me with the amount of dirt it was rolling — and still no engine lug-down. It had the power to work at the speed I wanted. And the cab is very quiet — no need for earplugs. But that said, it lets you hear enough to know how the machine's performing. Good seat, too, plenty of adjustment, including the armrests. I'd say a lot of thought went into the design of this tractor."

Schultheis went on to do a bit of experimenting on his own with the D51, including building a V-ditch and taking it up and over a steep, steep spoil pile. We then asked him for his overall take on the new machine.

"I haven't been on a tractor this size that moved as much dirt. This machine is very friendly to run — someone's taken the time to design it from an operator's point of view."

Schultheis also put the D51 to work constructing a V-ditch and noted that the machine's quick hydraulic response is a plus in this application.
In the slot-dozing exercise, Schultheis was impressed with the D51's ability to keep a large load rolling.
Operator Jim Shultheis runs machines during the work season, then shares his expertise with up-and-coming operators at Local 649's training facility.
When you're in theseat, the D51's hood virtually disappears. Note the footpads adjacent to the monitor; the D51, with its low center of gravity, performs well on slope work.
The tractor's newly de-signed monitor provides fault codes to assist with diagnostics, and the center display indicates ground speed, with the "1/2/3" markings equating to gears in a conventional powershift. The D51 is equipped with Komatsu's remote monitoring system, Komtrax, which the buyer can use free of charge for five years.
The cooling package canbe swung up even if a rear-mounted attachment is used. The fan is reversible for cleaning the heat exchangers, and even though the system is designed to pull most of its cooling air through perforated panels at the rear of the machine, it does draw some air from the engine compartment for added cooling. Isolation-mounted steel tubing conveys coolant between the engine and the aluminum radiator.
When grading in rough terrain, Schultheis noted that the glass in the doors allowed a distortion-free view of the work area.
On a long push up and across a large berm, the Komatsu D51PX-22 handled big loads with no track-slip and no engine lug-down.
In downhill dozing, Schultheis said the D51 exhibited a flat-footed stability.
We're not sure, but we thinkthe Komatsu guys went a little pale when Schultheis took their tractor up and over this 30-plus-degree pile of loose spoil.
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