| February 01, 2010 |
How to inspect a used mid-size excavator
Pay particular attention to two key areas: undercarriages and hydraulics.
By Marcia Gruver
Thoroughly inspecting a used excavator takes between one and two hours, so go into it with clear objectives. Know exactly how you plan to use the machine – including application and whether it will be a primary or backup machine – and how much you’re willing to spend to get it in operating order.
To get an overview of what goes into this inspection, we talked with Howard Abell, former vice president of sales with Flagler Construction Equipment, a Volvo dealer in Orlando, Florida, and now president of Advantage Construction Equipment & Parts. Dennis McDavid, Flagler’s used equipment manager, assisted in the inspection. The model up for inspection came from Flagler’s rental fleet: a Volvo EC210C with 1,394 hours.
There are a few basic tools needed to inspect an excavator: a track measuring group (available from most equipment dealers), stop watch, 25-foot tape measure, magnetic dial indicator and a clipboard for recording measurements and observations. Some manufacturers have inspection checklists you can download from their websites or you can use the one we’ve attached to the digital version of this article. Write down the model and serial number, usually located in excavators near the floor on the outside right side of the cab. Note the number of hours.
Perhaps even more important than having the proper tools at the ready is choosing the right person to serve as your machine operator during the inspection. “You want to make sure the person you’re working with understands what you’re saying and what you want to do,” Abell says. If you’re working with an operator you haven’t worked with before, make sure he knows your hand signals. And be defensive. “Try not to put yourself in a position where if something happens, you’ll get hurt,” Abell says. “Steel doesn’t have much mercy.”
Before getting down to specifics, go on a walk-around to get a general impression of the machine’s wear. Look for cracks, especially on weld seams, although cracks can appear anywhere. Plating will tell you the previous owner has put a plate over a crack for reinforcement. Abell feels cracks and/or any resultant plating will tell you a machine has been improperly used. “Cracks decrease the value of the machine around 20 percent,” he says. While you always have to judge a machine based on how you plan to use it, Abell says he steers clear of small and mid-size excavators that have cracks.
Also look for any oil seepage in the boom and stick cylinders. If a cylinder is seeping and looks resealable, calculate $2,500 per cylinder to fix the problem. In this initial walk around, note if there are any torn hydraulic lines and if all the brackets are in place.
Sheet metal damage, while usually not a major cost item, still needs to be factored in. Cab cosmetics and functionality should be noted. How worn is the seat? Are all gauges working? Is there any missing or broken glass?
Take advantage of the computer diagnostics in today’s machines. Note any error codes. And if it’s a low-hour machine, pay a manufacturer’s dealer to run a complete diagnostic/history report, downloaded from the machine’s computer. (See sidebar below.)
Look under the lower housing to see if oil is dripping underneath. Since excavators are primarily hydraulic machines, a hydraulic leak could signal a major problem. While a leak could just mean a relatively inexpensive seal replacement, if oil is leaking out of the hydraulic pump you might have to replace the pump, which would cost around $12,000 to $15,000.
Now that you’ve gotten an overview of the machine, it’s time to get specific with the undercarriage: tracks, drive sprocket, idlers and rollers. Although some contend they can visually determine how much wear is on an undercarriage, Abell says the only way you can truly determine wear is to measure it.
But first, look at the rail pins and bushings. As the pins and bushings wear internally, each track segment lengthens and becomes looser. To take up the slack, the front idler is moved forward in a bracket on the rails between the idler and the rear drive sprocket. There will come a point, however, when no further adjustments can be made. Some excavator owners will then make the bad decision of taking a link out. While this makes the track look tighter, it also creates a tremendous amount of internal wear. You can count the links and compare them with how many are supposed to be there, but Abell says the best way to see if an undercarriage is worn out is to measure it using a track measuring group, which costs about $250 and is available from most dealers. Here’s an overview of the key undercarriage measurements:
Grousers: Take the depth gauge from the track measuring group (it looks like a flat bar), and lay it across the pad, then set the rod on the gauge to the depth of the grouser. Use the ruler in the track measuring group to determine how deep the rod is set. Compare the measurement to the manufacturer’s “new” and “limited use” numbers, as published in the machine’s service manual (an OEM dealer can also give you these numbers). How close your measurement is to either one of those numbers will help you determine grouser wear.
Rails: Using a measuring tape, measure from the outside of one pin to the outside of another pin five pins way. Once again, compare it the manufacturer’s published “new” and “limited use” numbers to determine what percentage of use remains.
Links: One wear point is the flat area on the links that run over the rollers and idlers. Put the depth gauge from the measurement group against the bottom of the link and then position the rod from the gauge so it hits the bottom of the pad. Measure the depth of the rod and then compare against the manufacturer’s numbers.
Carrier rollers tread diameter (top rollers): Taking the caliper from the track measuring group, work it over the roller’s outer diameter. Bring it out and measure the distance between the two prongs of the caliper. Again, compare your measurement with the new/limited use scale.
Guide rollers tread diameter (bottom rollers): Reposition the machine so that the track you’re measuring is lifted off the ground. Guide rollers are measured the same way as carrier rollers. Be sure to measure each roller independently, taking care with the front roller and back roller, both of which experience more wear.
Sprockets: This is a more subjective observation. If the sprockets are pointed it’s a sign they are worn. Some manufacturers have a see-through sprocket gauge included in its track measuring group that visually lets you know how much wear is left.
Bushings: Measure with calipers and calculate the wear from the manufacturer’s chart.
Use your individual component measurements and observations to determine a wear calculation for the entire undercarriage. If the entire undercarriage needs to be replaced on a machine this size, it will run around $12,000.
Examine the machine for wear on all the pins and bushings throughout the linkage on the boom, having the operator work from a side loading position using a cycle that first puts down pressure on the bucket and then releases it. Each time the operator cycles the machine, check for any movement in the bushings. Look at each bushing independently. Abell first checks the bucket pins and bushings, instructing the operator to take the bucket completely off the ground.
“Loose pins and bushings are a key sign of how the machine has been treated,” Abell says. “It also tells me that they maybe didn’t properly grease the machine.
For a 20-metric-ton machine such as the one we’re inspecting, you should virtually have no movement in the swing bearing. “If you can see any movement in a swing bearing on a machine this size, it’s probably too much,” Abell says.
Beyond the visual inspection, use a magnetic dial indicator to take a measurement at four quarter turn positions; an average of these four measurements will tell you what kind of shape the machine’s swing bearing is in. “Without this measurement, you’re guessing at the amount of wear in the swing bearing and this is a costly repair item,” Abell says.
Since excavators are hydraulic-centric machines, checking out the hydraulic pressure and flow is critical. Using a stop watch, time how long the machine takes to do several tasks. A couple of examples: test the boom cylinder speed by fully retracting the arm cylinder and fully extending the bucket cylinder, then raise and lower the boom, timing each up and down motion. To test the arm cylinder, with the bucket cylinder fully extended, time how long it takes to move the arm from the full-out position to the full-in position. Then time how long it takes to return to the full arm out position again. Do each test three times and average your numbers. Then compare your times with manufacturer published times.
To test the track running speed, tie a ribbon on one of the track shoes on the side being tested, jack up the track being tested, then time how long it takes to do three track rotations at maximum speed. Apply the test to both tracks, forward and reverse. Also tram the machine to make sure it trams in a straight line – if it trams one way or the other you could have a pump that’s getting weak.
Check for drifting – also called creeping – by raising the boom with a full load in the bucket, then turning the machine off. Wipe the oil off the boom cylinder rod and mark the measuring start point with a piece of tape.
After five minutes, measure again to see how much it has drifted down. (Remove the tape and clean carefully.) While a certain amount of drift is acceptable, excessive drift could be a sign of packing in the cylinder, or oil bypassing internally in the control valves or cylinder.
Toward the end of your inspection, after the machine’s been running a bit, take another walk around, opening up service doors, and looking underneath to check any leaks that appear after the machine’s been running awhile.
Also look at the swing gear box and motor, making sure the oil is clean on the dipstick and that no water is present. And check the engine dipsticks, looking at how black the oil is, which will tell you how long it’s been since it’s been changed. Check also for moisture and blow-by, which sometime you can feel coming out of the dipstick compartment. EW
Editor’s note: This article is intended as a checklist of considerations when buying a used excavator, not as an all-inclusive used equipment buying guide.
Get the printout
Computer diagnostics on machines produced in the past five years or so can give you a wealth of information. For example, by using Volvo’s MATRIS program on the EC210C used for this article, you could find out:
• 96 percent of the time the engine coolant temperature was between 167 and 208.4 degrees.
• 47 percent of the time the machine was operated in “heavy” mode.
• 33 percent of the time the engine idled three to 10 minutes before shutdown.
• Hydraulic oil temperatures ranged from 140 to 176 for 558.3 hours