Excavator line boring is the repair you need when the hole in the boom, arm or bucket has worn, not just the pin and bush inside it. The worn bore is built up with weld if needed, machined back round on one straight axis, and fitted with a new bush and pin. Whether it pays depends on how many joints are worn, on-site or workshop, and how many idle days each route costs you at roughly ₹16,000 to 25,000 a day for a mid-size crawler excavator (indicative, as of Jul 2026).

The operator says the boom “knocks” when it changes direction. You change the pin and bush at the arm joint, and a week later the knock is back. That second knock is the one that matters. It usually means the hole the bush sits in has worn oval, and no new pin will sit true in an oval hole.

This piece is about that repair: how to tell you have reached it, the routes for fixing it, and the money lines that decide between them.

Pin and bush job, or a line boring job?

A pin carries the load and lets the joint turn. The bush is a replaceable sleeve pressed into the hole in the boom, arm or bucket, so that the pin wears the bush and not the steel of the arm. Our guide to pins and bushes on excavators and backhoes covers how they work and how to spot ordinary wear.

The bush is meant to wear out. Trouble starts when it is left too long. Once the bush wears through or spins in its hole, the pin and the bush start working on the steel of the boss itself. From then on you are not replacing a part, you are repairing the machine.

Pull the pin and look at three things:

  • The bush. Has it turned in the hole? Score marks around the outside of a bush show it has been spinning.
  • The hole. Is it still round? A pin that is tight one way and loose the other is sitting in an oval bore.
  • The two sides. Most joints have a boss on each side. If the left and right holes have worn differently, the pin is no longer straight across the joint.

If only the bush is worn and the hole is round and in line, a new pin and bush will do. If the hole has worn, you need excavator line boring.

What excavator line boring actually does

The “line” is the point. A pin passes through two or more bosses, and all of them have to share one centre line. Boring each side separately can leave the pin bent across the joint, and a bent pin wears new bushes fast. A line boring bar runs through both bosses at once, so every hole is cut on the same axis.

The usual sequence is:

  1. Measure the worn bore and check how much steel is left in the boss.
  2. If the bore is oversize, build it up with weld, often with an automatic bore welder that lays a spiral bead around the inside of the hole.
  3. Bore it back to the finished size, on one axis through every boss.
  4. Face the outer edges if they are worn, so shims and the bucket or link sit square.
  5. Press in new bushes and fit new pins.

The finished size is what you are paying for, so ask for it in writing. Machined holes are specified to a tolerance class under the ISO system of limits and fits, which India publishes as IS 919 (Part 1): 1993. A class is written as a letter for the position of the tolerance and a number for its grade, such as H7, with capital letters for holes and small letters for shafts. Ask the machinist to write the finished bore diameter and its tolerance on the job card, next to the bush size it is meant to take.

Four ways to fix a worn pin hole

Route When it fits What you pay for
New pin and bush only The hole is still round and in line; only the bush and pin are worn The pin and bush kit, and fitting
Bore oversize, fit a thicker bush The hole is worn but the boss still has enough wall thickness Boring time, a special oversize bush, the pin
Weld build-up and line bore to original size The hole is well oversize or the boss walls are thin Welding hours and consumables, boring time, standard bush and pin
Replace the boom, arm, link or bucket The boss is cracked, or there is too little steel left to weld The new part, and fitting

The oversize-bush route skips welding, but it leaves you with a non-standard bush that you will have to source again next time. The weld-and-bore route returns the joint to the original drawing size, so the standard kit fits again. Many owners prefer that, especially on a machine they plan to keep.

Cracks change the answer. A crack running from a boss into the arm plate is a structural repair first, and our guide to excavator boom repair, cracks and welding covers when that becomes a replacement.

On-site boring or a workshop?

Portable line boring equipment clamps onto the boom or arm and cuts the hole where the machine stands. A workshop job usually means taking the attachment, arm or boom off, loading it, and bringing it back.

Question On site Workshop
Strip-down needed Usually only the pin and bush The arm, boom or bucket comes off
Transport The crew comes to you Loading, a trailer, and the trip back
Idle days Usually fewer Usually more
Best for One or two joints on a working machine Several joints, or an arm with cracks that also needs plate work

Neither route is better by default. A workshop with the arm on a bench can do more at once. An on-site crew saves the days in between. Ask both for the same thing: the joints covered, weld build-up or not, the finished bore size, the bushes and pins included, and the number of days.

What decides the excavator line boring cost

We are not printing a single rupee figure, because a single bucket-link joint and a full boom-foot, arm and bucket job are different repairs. These are the lines that move the bill:

  • The number of joints bored, and their diameter. Bigger machines mean bigger pins and longer boring time.
  • Whether the holes need weld build-up, and how much.
  • Callout or transport: the crew’s travel to you, or trailer hire to the workshop and back.
  • Strip-down and refitting labour, which grows fast if the boom has to come off.
  • New pins and bushes. Every bored joint needs them, and they are a separate purchase.
  • The days the machine stands idle.

The last line is often the biggest. Our equipment downtime cost estimate puts an idle day for a mid-size crawler excavator at about ₹16,000 to 25,000 (indicative, as of Jul 2026). So if one quote takes three days fewer than another, that quote is worth roughly ₹48,000 to ₹75,000 more to you before you even compare the invoices. Use your own day rate if you know it.

The bucket is often where the first worn boss shows up. If line boring is one of several jobs on an old bucket, set the total against a new one using our excavator bucket repair cost breakdown.

Questions to ask before you agree

  • Which joints, and how much play does each one have now? Ask for the measured bore sizes before and after.
  • Will the holes be welded and bored back to standard size, or bored oversize for a special bush?
  • Are the pins and bushes included, and are the pins hardened?
  • How many days will the machine be off work?
  • What warranty does the shop give on its own work, in months or hours?

Keep the next one away

Line boring is almost always the bill for a bush that was left in too long. Most pins in India run in plain steel bushes greased through a nipple every shift. Some makers fit grease-holding bushes with longer intervals. Hitachi, for example, states 500 hours for front greasing on its compact Zaxis excavators and 100 hours for the bucket joint. Our guide to greasing points and intervals lists them. Change pins and bushes while play is still in the bush, and the steel around it never wears.

If you are buying a used excavator, rock the bucket and arm by hand before you agree a price. Play at three or four joints at once is a line boring bill waiting to land on the new owner.

The bottom line

If a new pin and bush still knock, measure the hole. A worn bore needs line boring: weld build-up where needed, a straight bore through every boss, and new pins and bushes. Get the finished size in writing, and compare quotes on idle days as well as price.

If the boom, arm and undercarriage all need money at once, price a newer machine before you spend. The Tata Hitachi EX 210 Infra and Hyundai R210 Smart Plus are the most asked-about 20-tonne-class models; browse all live excavator models and prices, check equipment finance options, or source parts through spare parts enquiries.

Repair costs, downtime figures, greasing intervals and warranty terms vary by machine, region and workshop, and change over time. Confirm the scope, finished sizes and price with your OEM dealer or the workshop before you commit to a repair.