Backhoe Loader (JCB) and Excavator Engine Mounting: Types, Failure Signs and Fitment

A backhoe loader that has started shaking the cab more than it used to at idle, or gives a heavy clunk every time you change from forward to reverse, very often has a worn engine mounting. The mountings are the rubber-and-steel blocks that hold the engine on the chassis, and when the rubber cracks, sags or goes soft with oil, the engine starts to move about on its frame.

Most people in India call every backhoe loader a JCB, and the JCB engine mounting they search for works the same way on every make and on excavators too. This guide explains what an engine mounting does, the main types, the signs that one has failed and how to check it yourself, which engine family your machine carries, and what to tell the dealer before you buy a replacement. It gives no prices, because these change with the machine, the mount type and the seller.

What does an engine mounting do on a backhoe loader or excavator?

It does three jobs at once.

First, it carries the weight of the engine and holds it in place on the chassis, through bumps, digging shocks and slopes. Second, it stops most of the engine’s shaking from reaching the frame, the cab and the operator. A diesel engine shakes all the time it runs, more at idle and when it is pulling hard. Third, it keeps the engine lined up with whatever it drives. On a backhoe loader that is the torque converter and gearbox behind the engine. On an excavator it is the main hydraulic pump, which bolts to the back of the engine through a flexible coupling.

The rubber is what makes the second job possible. Wikipedia’s article on vibration isolation lists moulded and bonded rubber mounts as the usual way machinery such as engines is isolated from the structure it sits on. Rubber bends a little under a shaking load and soaks up part of the energy, so the frame feels much less of it. Steel bolted straight to steel would pass all of it on.

A mounting can only do this while the rubber is in good condition. Once the rubber hardens, cracks, tears away from its steel plate or swells with oil, all three jobs start to fail together.

What types of engine mounting are used on construction machines?

Four shapes cover nearly every machine. Which one your machine uses, and how many, is set by the maker for that model, so the parts book for your machine’s serial number is the only reliable answer.

Many mounts carry a rebound stop: a steel washer or plate that limits how far the engine can lift. It also keeps the engine captive if the rubber tears right through, which is why a broken mount often clunks rather than letting the engine drop.

Engines commonly sit on three or four mounting points, usually with a pair at the front of the engine and a pair at the flywheel or gearbox end. The rear mounts carry the most load on a backhoe loader, because the gearbox hangs off that end.

What is the difference between engine mounts and cab mounts?

They do the same job for different parts. Engine mounts keep the engine’s shaking out of the frame. Cab mounts keep what is left of it, plus the shocks from digging and travel, out of the operator’s cab.

Excavator makers publish their cab mounts because operator comfort sells machines. The JCB NXT 215LC cab sits on six viscous mounts, and the SANY SY220C-9HD lists silicone viscous cab mounts. Engine mounts are almost never listed on a spec sheet at all.

This matters when you are chasing a vibration. If the whole machine shakes when you rev the engine, look at the engine mounts first. If the engine looks steady but the cab rattles and booms while the frame does not, the cab mounts are the more likely cause.

What are the signs of a bad engine mounting?

The first sign is usually more vibration than you are used to. Operators feel it in the seat, the floor and the steering wheel long before anything looks broken. The table sets out the common signs, what each one usually means and what to look at.

Two of these deserve a closer look. Fan damage is common after a mount fails, because the fan is fixed to the engine but the shroud and radiator are fixed to the frame, and the small gap between them closes when the engine sags. A belt that will not stay tight is often blamed on the belt; the fan belt guide covers belt tension, but check the mounts before you fit the third belt in a month.

On an excavator, engine movement also loads the coupling between the engine and the main hydraulic pump. A rhythmic knock from the back of the engine on a machine with worn mounts should be checked by a mechanic before the coupling or the pump shaft is damaged.

How do you check an engine mounting yourself?

Most of the check is done with the engine switched off, and none of it needs special tools.

1. Make the machine safe. Park on level ground, lower the front shovel and the backhoe bucket (or the excavator bucket) to the ground, stop the engine, take out the key and let the engine cool.
2. Look at each mount. Use a torch. You are looking for cracks in the rubber, rubber peeling away from the steel, a mount that is squashed flat on one side, and rubber that is wet and black with oil.
3. Check the bolts. Every mounting bolt should be present and tight. A loose bolt lets the mount move and wears its holes oval.
4. Lever test. Put a long bar between the engine and the frame next to a mount and lever gently. A good mount moves a little and springs back. A failed one lets the engine move a long way, or you can see the rubber split open as you lever.
5. Watch it run. With a trained operator in the seat and the machine parked as in step 1, have the engine started and revved from idle to full and back while you watch from the side, well clear of the fan and belts. A healthy engine twists slightly and settles. An engine that jumps, or lifts clearly on one side, has a failed mount on the side that lifts.

Never put a hand near the fan, belts or pulleys while the engine is running, and never lever against a running engine. If you are not sure what you are seeing, have the dealer’s mechanic do step 5.

A good time to check the mounts is at every major service. The construction equipment service schedule sets out what is done at each interval, and a look at the mounts takes five minutes while the engine covers are already off.

Why do engine mountings fail early on Indian sites?

Age alone wears out rubber slowly. Mounts that fail early nearly always have one of these causes behind them.

• Oil and diesel leaks. Engine oil and diesel soften and swell ordinary rubber. A leaking rocker cover or fuel line above a mount can ruin it in months.
• Heat. Mounts close to the turbocharger or the exhaust manifold run hot, and hot rubber hardens and cracks faster.
• Shock loads. Breaker work, dropping a loaded bucket hard, and fast forward-reverse changes under load all jerk the engine against its mounts.
• Loose bolts. A mount that is not held tight hammers back and forth and tears itself apart.
• One new mount among old ones. If only the broken mount is changed, the new one carries more than its share of the load and the old ones keep the engine sitting out of line.

Mounts are also often changed during a full engine rebuild, when the engine is out of the machine anyway. The engine overhaul kit guide explains what is replaced at that stage.

Looking for a machine instead of a part? Compare backhoe loader models and prices and connect with a dealer.

Which engine does my machine have, and does it decide the mount?

The engine family is the first thing a parts counter asks for, but it does not settle the mount on its own. The mounting brackets on the frame belong to the machine maker, so the same engine can sit on different mounts in two different machines.

Backhoe loaders sold in India use four-cylinder diesel engines from several makers. The table shows the engine each named machine lists, taken from the machine’s own spec sheet.

Fitment varies by model, model year and serial number, so always confirm the part with the manufacturer or an authorised dealer before you buy.

The last row shows why the engine name is not enough. Three makers’ 20-tonne excavators list the same Cummins 6BT 5.9 engine, yet each maker designs its own engine bay and brackets, so a mount for one is not automatically right for the others. The same holds for backhoe loaders that share a Kirloskar engine. The backhoe loader parts guide and the excavator parts guide show where the engine sits in each machine.

What should you tell the dealer when buying an engine mounting?

Take enough information that the parts counter can find the exact part the first time.

• The machine model and its serial number, which is stamped on a plate on the frame (often called the PIN or chassis number).
• The engine model and engine number, from the plate or sticker on the engine block.
• Which mount you need: front or rear, left or right. They are often different parts.
• A clear photo of the old mount, and any part number moulded into its rubber or stamped on its steel plate.

Ask whether the mounts should be changed as a pair or a full set, and whether new bolts and nuts are needed. Mounting bolts are tightened to a set torque in the workshop manual, and many workshops fit new ones with new mounts.

What drives the price of an engine mounting is mostly its type and size. A plain sandwich mount is a simpler part than a cone mount with its rebound washer, and a fluid-filled mount is the most complex of the four. A mount sold with its steel bracket costs more than the rubber part alone. The rear mounts on many machines are larger than the front ones, because they carry more of the load.

For the bigger picture of how the engine and the other systems fit together, the guide to excavator components walks through each one, and the parts and running costs guides cover the other wear parts on these machines.

If a worn-out machine is costing more in repairs than it earns, compare excavator models and prices or backhoe loaders and talk to a dealer about a replacement.

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.