The Difference Between a Good Used Excavator and an Expensive One Is Often Just a Few Cylinder Checks

Inspecting Hydraulic Cylinders on a Used Excavator: What to Look For

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I remember watching a contractor buy a used excavator a few years back. He checked the engine, looked at the tracks, fired it up, moved the boom and bucket a couple times, and handed over a bank check. Two weeks later, he was on the phone with a hydraulic shop getting a quote to repack the boom cylinder. That machine ended up costing him an extra three grand before it ever dug a real trench. The thing is, he could have caught the problem in about ten minutes if he knew what to look for.

When you're looking at a used excavator, the hydraulic cylinders tell you more about the machine's real condition than almost anything else. Engine hours can be rolled back. Undercarriage parts get replaced. Paint gets freshened up. But cylinders? They show every bit of wear and abuse the machine has seen. And unlike a worn track shoe, cylinder problems don't always show up as leaks right away. Sometimes they just drift a little. Sometimes they only act up when the oil gets hot. You have to dig a little.

Start with the rods. Walk around the machine before you even start the engine. Every cylinder rod should have smooth, shiny chrome. Run your hand along each rod if you can. You're feeling for nicks, scratches, or rough spots. A small scratch near the wiper seal might not leak today, but it will start cutting that seal the moment the cylinder cycles. Once that seal fails, dirt gets into the cylinder, and then the rod wears faster, and pretty soon you're not looking at a simple seal kit anymore. You're looking at a full rebuild with a new rod or rechroming. That gets expensive fast.

Also look at the rod surface near the gland when the cylinder is fully extended. Pitting there tells you the machine sat outside for long periods without being used. Rust forms, pits develop, and every time that rod moves, those pits scrape against the seal. That machine has probably been sitting for months, which means other seals in the system might have dried out too.

Now look at the cylinder tubes. Dents are a big deal. A dent might not leak, but it can push the tube wall inward enough that the piston seals hit a deformed surface every time they pass that spot. Those seals wear unevenly and fail early. I've taken apart cylinders where the piston had actually gouged the inside of the tube because the dent was deep enough to reduce the clearance. That's not a reseal job. That's a new cylinder tube or an entirely new cylinder.

Check the welds where the cylinder mounts attach to the machine. Hairline cracks around the pin connections are common on high-hour machines. A small crack you can see with a good flashlight might be weldable. But if you see old weld buildup and grinding marks, someone has already fixed that crack before. That tells you the machine has seen heavy shock loading. That same shock loading might have stressed other parts you can't easily inspect.

Once you finish the visual check, start the engine. Let the hydraulic oil warm up completely. Cold oil is thick and will hide internal leaks that become obvious when the oil is hot. I usually run the machine for a good ten or fifteen minutes, cycling everything gently, before I do any serious testing. You can tell the oil is warm enough when the hydraulic tank feels hot to the touch.

Cycle each cylinder through its full range of motion several times. Watch the speed. A cylinder that moves slower than the others might have a bent rod or a damaged piston. Listen for odd noises. A grinding sound usually means contamination inside the cylinder. A squeal can mean a relief valve is opening because something is binding. A knocking might be a loose piston nut. Any of these means the cylinder needs to come apart.

The drift test is the most useful thing you can do. Park the machine on level ground. Extend the boom and stick so the bucket sits flat, then lift the tracks just barely off the ground. Shut the engine off. Mark the cylinder rod positions with a piece of tape or just remember where they are. Wait five minutes. Come back and look. If the tracks are back on the ground, you have internal leakage. A little drift is normal on older machines. But if the machine settles more than a couple inches in five minutes, those cylinders are worn.

While the machine is running, look at each cylinder gland. A little film of oil around the wiper seal is normal on a machine with some hours. A drip is not. And if you see oil running down the outside of the tube, that seal is completely gone. Some sellers will wipe the cylinders clean before you arrive. That's why you run the machine for a while before checking. A fresh clean spot on an otherwise dirty cylinder tells you someone was hiding something.

Take your time with this inspection. Most cylinder problems aren't hidden. They're right there in plain sight. You just have to look.