Komatsu PC138US-8 excavator

By: John Clark, Photography by: John Clark


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Zero swing excavators like Komatsu's PC138US-8 are becoming more popular as contractors and operators discover their versatility.

Komatsu PC138US-8 excavator
Komatsu PC138US-8 excavator is considerably more stable on non-zero swing machine when operating on steep slopes.
  • Operator-friendly cab
  • Smooth and fast hydraulics
  • Long list of standard features
  • Easy and quick servicing
  • Feels well balanced and stable

The Komatsu PC138US-8 is the latest excavator from Komatsu in the 13-tonne class, zero tail swing version. I have owned it since June 2007 when I bought it new, and have operated it for 3600 hours.

The decision to buy a Komatsu was based on price and specification. In New Zealand the PC138US-8 comes as standard with a dozer blade and a proper bolt-on cutting edge, and a rear view camera and GPS monitoring known as Komtrax. Also standard are factory fitted quick hitch piping, auxiliary lines for one-way flow and double acting hydraulic attachments. The standard factory cab is ROPS certified and has safety valves on the boom and dipper rams, which make it legal to use as a crane. All these features were extras on the other brands I looked at - which really push the price up.

Engine access

Engine access is straightforward and you can also check the swing box dipstick and filler point easily. Servicing is no harder than a non-zero tail swing digger.

Greasing the Komatsu is also quite simple; the PC138-8 handbook says you only have to grease it every 500 hours. Personally I think that's too long when it is being worked hard; I've found once a week is more than enough.

The computer checks the engine oil and water for you when you switch on the ignition.

In the cab

The sliding convex door is easier than the swing-open type used on most machines. Two grab rails give you easy access to the adjustable suspension seat.

Although there isn't much storage space, there's a cup holder, an ash tray, a pocket in the back of the seat and a magazine rack.

To the front is a large windscreen with Komatsu's unique wiper system, which is mounted on the cab's right-hand side rather than through the glass itself to increase visibility.

A lever positioned on the right-hand side of the seat is for blade control; in front of this is the monitor panel, which has a whole host of functions usually just showing water temp, hydraulic temp and fuel level along with the time working mode and tracking speed that you have selected. There are six more buttons at the base of this screen that switch on the rear view camera, a maintenance function and oil flow adjustments, to list just a few. Underneath this screen are more buttons to select windscreen wiper functions, tracking speed, automatic idle, warning buzzer stop, and working modes.

There are five working modes: power, economy, breaker, lifting and attachment. I tend to just use the attachment mode as this is the same as power mode; the only difference is the auxiliary lines work as well.

Performance and handling

Starting the PC138US-8 is the same as most machines except it has a warm up mode, which runs the engine above low idle until it reaches a safe operating temperature, then drops the revs back down again. Once everything is up to temperature and the throttle dial has been turned up I lower the safety bar and gently pull back on the hand levers, which are the ISO pattern, and the revs automatically cut in.

There is a 3m dipper arm on this digger, the extra bit of reach making all the difference for work like digging a pond.

The ground was very dry and the 1800mm wide Wedgelock tilt bucket was on for stripping topsoil. To start I used the digger in attachment mode as this delivers an extremely smooth power that is excellent for swinging a full bucket load at reach over the side. The machine feels well balanced while operating with a tilt bucket.

Once the soil is stripped I started to dig into the Moutere clay, positioning the PC138-8 with the dozer blade at the rear while still using the tilt bucket. I was able to peel a good load out each cycle and after a short time there was a big pile of clay set aside.

Swinging around to use the dozer blade, I lifted the boom up, pulled the dipper arm in and started to push. The dozer has a good shape for rolling material along; I pushed up through the clay pile in the low tracking speed without any problems. With the rear view camera I did not need to turn around to reverse back down, as I could see the back of the tracks and a good distance behind quite clearly.

I then switched to high-speed tracking and went for another push. As the blade started to roll clay forward the engine had a power boost that cut in and it just kept pushing. I then returned to digging and soon had the job done.

On another pipeline job I used my 1150mm wide wedgelock digging bucket and dug a trench for a 900mm concrete storm water pipe, lifting pipes and slotting them into position with ease.

I find the PC138US-8 much more stable than a non-zero swing machine on steep slopes, as it's heavier than its siblings and doesn't have a big back end hanging over the side of the tracks. You've also got a blade to use as an anchor.

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