An excavator boom repair is structural work on the big curved steel arm that carries the bucket: re-welding a cracked section, building up worn pin holes, or fitting a new boom when the steel is past saving. It is metal work, not hydraulic work. A boom that sinks down on its own has a sealing fault, while a boom that has cracked has a steel fault, and the two go to different workshops.

The boom is the first and largest section of the front end, joined to the machine at the boom foot. The arm (many operators call it the stick or dipper) pins to the far end of the boom and carries the bucket. Neither is a solid bar: both are hollow boxes of welded steel plate, which is why they crack at a weld long before they ever bend.

For how the boom is built and which boom type suits which job, read our guide to the excavator boom. This guide stays with the steel.

What gets repaired on an excavator boom?

Three things go wrong, and they are not equally serious. The cheapest is a worn pin bore, the round hole a connecting pin sits in. Every front-end joint runs on a steel pin inside a bushing with grease the only thing between them, so starve the joint and the pin wears the hole oval. A workshop machines it out and welds in a new bushing. Left alone, an oval hole lets the arm knock about, and that knocking starts a crack in the plate around it.

Cracks in the welded steel are the repair this guide is about: they start small, grow slowly, and almost never appear where an operator is looking. A bent or twisted boom is the end of the line, because the pin centres no longer line up and no amount of welding puts a twist back. The pins and bushings themselves are ordinary wear items, covered with the rest of the front-end hardware in excavator parts and their names and excavator components.

Where do excavator booms and arms crack?

Booms crack where the shape changes and where the welds are, not in the middle of a flat plate. Steel under repeated loading fails where stress bunches up, and on a boom those places are predictable. Learn the six and an inspection takes ten minutes.

  • Around the boom foot, where the boom pins to the machine and every load the bucket ever lifted passes through a hand-sized patch of steel.
  • The boom nose, the forked end where the arm pins on, especially around the pin bosses (the thick steel collars welded around each pin hole).
  • The cylinder mounting ears, the brackets the cylinders push against, which take the full push of the hydraulics in one small spot.
  • Along the box corners, the long seam welds running the length of the boom, usually starting at one end and creeping along.
  • The arm nose near the bucket pins, the busiest joint on the machine and the one most often run dry of grease.
  • Beside an old repair. A previous weld leaves a hard, brittle band in the steel next to it, and a new crack often starts there rather than in the weld itself.

The cause is nearly always fatigue. A fatigue crack is damage from loading a part over and over, not from one big overload. Nothing dramatic happens on the day it starts: the boom takes the same load it has taken ten thousand times, and this time a tiny flaw at a weld edge opens by a fraction of a millimetre. Then it does it again the next day.

Two habits bring that day forward. Side-loading is the first, which means swinging the machine to drag or push material sideways with the bucket, twisting a structure built to take loads front to back. The second is working a hydraulic rock breaker without easing off, because a breaker sends thousands of hammer blows a minute back up the arm into the boom.

How do you check an excavator boom for cracks?

Wash the boom, park it low, switch the machine off, and then look along every weld and around every pin boss in good light. That is the whole method, and the washing is the part people skip. A fatigue crack is a dark hairline, often no wider than a pencil mark, and a film of grease and dust hides it completely.

Four signs are worth knowing, because a crack rarely announces itself as a gap you can see through:

  • A fine dark line that does not wipe off. Dirt smears. A crack stays.
  • A rust or oil weep in a straight line. A crack breathes as the boom loads and unloads, drawing moisture in and pushing a rust stain out; on a greasy boom it shows as a thin dark line of oil.
  • Paint lifting in a straight line. Paint is brittle and splits over a crack before the steel opens up.
  • A knock that has changed. A joint that was quiet and has started to clunk has moved, and movement with no new wear is sometimes a crack.

When something looks doubtful, a workshop settles it with a dye penetrant check: a coloured liquid is wiped on, left to soak into any crack, then wiped off, so the dye seeps back out and draws the crack as a clear line. It needs no power and costs very little. On thicker sections a repairer may use a magnetic check instead, which finds cracks just under the surface.

Build the look into your greasing round rather than making it a separate job, since greasing already puts an operator at the right height beside every pin. Those intervals sit with the rest of the machine’s routine in the excavator service schedule. On a machine you are thinking of buying, the same checks belong on the list in buying a used excavator, along with a hard look at any boom repainted in one place.

Should a cracked boom be welded or replaced?

That call belongs to the dealer or a structural repairer who can see the crack, not to the welder who happens to be on site. Where the crack sits matters more than how long it is, and the steel in a modern boom is not the mild steel a fabrication shop works with every day.

A crack is usually a repair case when it is short, sits in flat plate away from the main joints, and was caught early. Repairers normally drill a small hole at each end first, which blunts the tip and stops it running, then prepare and weld the length between. Replacement moves to the front of the queue when the crack runs through a pin boss or the boom foot, when there are several cracks rather than one, when a crack has come back beside an earlier repair, or when the boom is bent. A crack that has returned is telling you the first repair did not address why it cracked.

The reason to resist a quick site weld is that a bad weld is worse than the crack it covers. Welding heats the steel and lets it cool fast, leaving a hard brittle band alongside the new weld. High-strength boom steel is fussy about how fast that happens, so it often needs preheating and particular consumables. Get it wrong and the boom cracks again next to the repair, which is why a returning crack is such a common story. Ask the dealer for the written repair procedure for your model before anyone strikes an arc, and keep the paperwork: it is the difference between a repaired boom and an unknown one when you come to sell.

One more thing the crack might not be. If the boom drifts down on its own rather than having cracked, test for a leak instead, because that is a seal or valve fault and no welding will fix it. The test is set out in excavator boom drift. A grinding or clicking noise while slewing is a third, separate matter covered in the slewing ring.

Why do some booms crack sooner than others?

Because the load on a boom depends on how far out the weight is, not just how heavy it is. Hold a brick against your chest and it is nothing. Hold the same brick at arm’s length and your shoulder complains. A boom works the same way, and it is the reason a long-reach machine is a different animal from a standard one of exactly the same weight.

The machines listed at the time of writing make the point plainly. Taking every excavator that sits between 22 and 26 tonnes of operating weight, and splitting them into standard machines and long-reach machines, the front ends are not remotely alike.

Standard vs long-reach excavators in the 22–26 tonne class (figures as per the current Sep 2026 listings)
Published figure Standard machines Long-reach machines
Machines in this weight band 35 8
Boom length 5,650–6,000 mm (5.7–6.0 m) 8,140–10,350 mm (8.1–10.4 m)
Arm length 2,250–3,000 mm (2.3–3.0 m) 6,020–8,000 mm (6.0–8.0 m)
Maximum digging reach 9,305–10,260 mm (9.3–10.3 m) 15,030–18,361 mm (15.0–18.4 m)
Arm digging force, where published 105–144.5 kN (31 of 35 publish it) 44–61.7 kN (3 of 8 publish it)
Bucket capacity 1.0–1.85 m³ where a single size is quoted (16 of 35) 0.45–0.52 m³ (8 of 8)

Read the force row again, because it is the whole lesson. A long-reach machine of the same weight digs with roughly a third to a half of the force a standard machine has. That is leverage: the same cylinders pushing through an arm twice as long deliver far less at the teeth, so the makers fit a bucket about a third of the size to match.

A long-reach boom is therefore not a standard boom that happens to be longer. It is a structure working at full stretch most of its life, matched to a small bucket and modest digging force on purpose. Bolt a standard digging bucket onto a long-reach arm because it was lying in the yard, or take a long boom machine off canal work and put it to prising rock, and the cracking is no longer bad luck. Excavator digging force explains why a bigger bucket lowers the force at the teeth, and the full list of long-reach machines and their reach figures sits in dredging and desilting.

Two machines can weigh the same and carry completely different front ends, so operating weight is where choosing starts, not where it finishes. Compare the long-reach excavator models available against the standard machines in the same class before committing to a long boom.

Is it safe to keep working with a cracked boom?

Not for lifting, not for holding a load, and not at full stretch. A crack grows fastest when the boom is extended and loaded, which is exactly the position most lifting happens in, and a failure at full reach drops whatever is in the bucket from height.

Once you know there is a crack, stop the machine and get it seen by someone who can judge it, with photographs and a measurement if the repairer cannot come the same day. Mark each end with a paint pen and a date, so anyone looking later can see whether it is growing. If the machine must be moved, travel with the boom low and the bucket empty.

What not to do is carry on until the job finishes. A crack does not pause, and this is the one fault where the cheap option and the safe option are the same.

What does an excavator boom repair cost?

We are not printing a figure, and not out of caution. A boom repair is quoted job by job, and the same crack can differ several times over in price for reasons that have nothing to do with the crack. A number here would read as a budget and mislead you at the dealer’s counter. What moves the quote is worth knowing before you ask for one:

  • Where the crack sits. Flat plate is straightforward. A pin boss or the boom foot means machining and alignment work on top of welding.
  • Whether the boom comes off. A repair on the machine is a different job from one needing the boom removed, which means a crane, pin extraction and alignment on refitting.
  • Getting it there. A boom of 8 to 10 metres travels as an oversize load, and on a long-reach machine that alone can dominate the bill.
  • Who does the work. An authorised workshop with the maker’s procedure, versus a general fabricator. The cheaper quote is not the cheaper outcome if the crack returns.
  • Whether a new boom can be had. On an older or imported model, availability decides the answer before cost does.
  • Downtime. Usually the largest number, and the one no quotation shows you.

Ask for the quote in writing and itemised, and ask what is warranted and for how long. For how a repair quotation is put together on a major component, read what a hydraulic pump repair really costs. If the damage came from an accident rather than fatigue, check the policy first: structural damage is often claimable, and the equipment insurance providers listed will tell you what their cover includes.

Excavator boom repair: the short version

Booms crack at the boom foot, the boom nose, the cylinder mounting ears, the long box-corner welds, the arm nose and beside old repairs. They crack from fatigue, helped along by side-loading, breaker work and dry pins, and they show as a fine dark line, a rust or oil weep, or paint splitting in a straight line. Wash the boom before you look, or you will not see any of it.

Short cracks in flat plate, caught early, are weld repairs. Cracks through a pin boss, cracks that have come back, and bent booms are replacement territory. Either way the decision and the welding procedure come from the dealer or a structural repairer, because boom steel is not ordinary steel and a bad weld cracks again beside itself.

If you take one number away, take the force row above: at the same operating weight, a long-reach machine digs with roughly a third to a half of a standard machine’s force and carries about a third of the bucket. Respect that and a long boom lasts. Compare the excavator models and prices available and talk to a dealer about the front end your work needs. If the fault turns out to be hydraulic rather than structural, start instead at excavator boom drift.

Prices, specifications and features are indicative, vary by variant, location and date, and should always be confirmed with the official OEM or authorised dealer before any purchase decision. DesiMachines is not liable for decisions taken on the basis of information that may have changed after publication.