5 Hidden Problems in Used Excavator Booms and Arms (And How to Detect Them)

A Field Guide to Not Buying a Banana-Shaped Disaster

Let’s talk about the unsung muscles of every excavator: the boom and the arm. They don’t spin like a final drive. They don’t roar like an engine. But if they snap, bend, or warp—your entire machine becomes an extremely expensive statue.

Buying a used excavator? Or just a used boom or stick? Good for you—saves cash and saves the planet. But let’s be clear: there are gremlins hiding inside some of those steel monsters. And unless you know where to look, you might end up with a hairline crack that turns into a horror show mid-job.

This guide will walk you through the five hidden issues we see most often in used booms and arms. It's part technical, part practical, and all brutally honest—just how we roll at Vikfin.

🚩 Problem 1: Hidden Cracks That Love to Multiply

You ever see an excavator start a job with a smile and finish with a limp? Cracks in the boom or arm are often to blame—and you won’t always see them with your naked eye.

Where They Hide:

• Along the weld seams, especially around high-stress zones

• At the base of the boom where it connects to the swing frame

• Around the bucket linkage area

• Inside box sections, especially if water or dirt got in

How to Detect Them:

• Visual inspection with a torch and mirror (not your phone light!)

• Magnetic particle testing (MT) – Reveals surface and near-surface cracks

• Dye penetrant testing (PT) – Great for finding cracks in welds

What It Means:

If you see even a small hairline fracture, it’s time to walk—or get ready for some serious repair work. A cracked boom is like a cracked femur: not something you want to find out about mid-squat.

⚙️ Problem 2: Weld Fatigue From a Hard Life

Every time a boom digs, lifts, or swings, it flexes a little. Over years—and sometimes abuse—that flex adds up. And eventually, welds start giving up on life.

Red Flags:

• Rewelded sections with questionable workmanship

• “Cold” welds that haven’t fused properly

• Rust lines around welds (means cracking beneath)

Pro Tip:

If a weld looks like a drunken snake with a hangover, it wasn’t done by a professional. At Vikfin, we inspect welds like exes check Instagram—with brutal scrutiny.

The Fix:

Some weld fatigue can be repaired, but it’s got to be done by someone who knows what they’re doing—and ideally followed up with a proper stress test or ultrasonic inspection.

🔩 Problem 3: Pin Hole Distortion

Here’s a biggie. Pins and bushings on the boom and arm should sit snug like a hand in a glove. But what if the glove’s been torn, stretched, or hammered into shape by Thor himself?

Causes of Pin Hole Damage:

• Overloading

• Poor bushing replacement jobs

• Long-term wear with no maintenance

• Poor greasing (yes, it matters!)

How to Spot It:

• Look for egg-shaped pin holes

• Measure internal diameters with calipers—don’t eyeball it

• Check for excessive play or movement at the joints

Danger Level:

High. A distorted pin hole leads to sloppy operation, misalignment, and ultimately—structural failure. You might as well swing your bucket with a wet noodle.

🪛 Problem 4: Internal Corrosion (The Rust You Can’t See)

If a boom or arm has been sitting outside in a rainy yard (hello, South Africa), water can seep into the box sections through worn seams, cracks, or neglected drain holes.

What happens next? Rust starts forming from the inside out.

Symptoms:

• Rust lines near seams

• Bulging or warped panels (rust expands metal)

• Drain holes blocked with gunk

• General “soggy” feel to the structure

How to Detect It:

• Tap the boom with a hammer—dull thuds = internal rust

• Look inside inspection ports (if available)

• Feel for soft spots or oil weeping where there shouldn’t be any

Verdict:

Minor rust is manageable. Internal rot? Run. That boom is one bucket drop away from going full “accordion mode.”

🔍 Problem 5: Misalignment or Warping

A boom or arm that’s even slightly bent is like a pool cue with a kink—looks fine until you try to do anything straight.

What Causes It:

• Heavy impact (like rolling off a lowbed or slamming into a truck)

• Lifting loads beyond spec

• Cheap or improper repairs (especially heat-straightening with no stress relief)

What to Look For:

• Visual alignment – Does the boom curve like a banana?

• Use a straight edge or laser level to detect subtle bends

• Check that both arm sides are the same length from pivot to end

Operator Feedback:

If operators say, “She digs a bit sideways,” believe them. You can’t recalibrate crooked steel.

🧠 How to Inspect Like a Pro (Even If You're Not One)

You don’t need an engineering degree—just a flashlight, a ladder, and a willingness to get dirty. Here’s a basic checklist to use every time you inspect a boom or stick:

🔎 Visual Inspection:

• Cracks, rust, repaint spots

• Weld consistency

• Obvious bends or twists

🔩 Pin Area Check:

• Play in joints

• Bushing condition

• Roundness of pin holes

🧪 Test Methods:

• Dye Pen or Magnetic Particle Test

• Tap test (sound changes in rusted areas)

• Internal scope camera if available

⚖️ Measurement Check:

• Measure pin center distances

• Compare sides for symmetry

• Inspect tilt and rotation angles (especially in linkage arms)

🛠️ Repair or Reject?

Let’s say you spot one of these issues. Do you run? Not always.

OK to Repair:

• Surface cracks, if welded properly

• Minor pin hole wear (can be line bored + sleeved)

• Rewelded seams, if done by pros and tested

Red Flag Territory:

• Multiple deep cracks

• Rust bubbles under paint

• Internal corrosion

• Obvious warping

At Vikfin, we don’t sell booms or arms with structural flaws. Every part is inspected and cleaned.

The Hidden Cost of a Bad Boom

You might think you’re saving money on a cheap used boom… until it cracks mid-job.

What That Costs You:

• Down time

• Emergency welders

• Damaged cylinders and hoses

• Operator injuries

• Lost contracts

What’s peace of mind worth? More than a sketchy R12,000 boom with a suspicious patch weld.

🙋‍♂️ Ask These 5 Questions Before You Buy a Used Boom or Arm

1. Has it been crack-tested?

2. Any history of rewelding or reinforcement?

3. Are the pin holes original, line-bored, or sleeved?

4. Was it pressure-washed or stripped before inspection?

5. Is the seller offering any warranty or return policy?

If the answers are vague or dodgy—run, don’t walk.

📞 How Vikfin Can Help

We’re South Africa’s experts in used and rebuilt excavator parts for a reason. When it comes to booms and arms:

• We’ve seen every failure type you can imagine

• We stand behind what we sell

Need a reliable Komatsu stick? A repaired CAT boom with clean pin holes? We’ve probably got it—or know where to get it.

And if you’re unsure what to check, we’ll walk you through the inspection so you don’t get stuck with junk.

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Thinking of buying a used boom or stick?Call Vikfin first—we’ll make sure you’re not buying a steel time bomb.