Engine mounts are rubber blocks with a steel plate bonded into them. They cost very little and they hold the engine in place while absorbing the vibration it makes. When they fail, the engine starts hammering the frame instead of floating on it — and the damage spreads outward to everything bolted to that frame. This is one of the cheapest items on a Kobelco to replace and one of the most expensive to ignore.
What a mount does
A diesel engine is not a smooth rotating machine. Each power pulse torques the block, and at idle the shaking is worst. The mounts absorb that movement in three directions: vertical support for the weight, fore-and-aft control under acceleration, and lateral control when the machine swings or works on a slope. The rubber is doing all three jobs at once, which is why a mount that looks fine from above can be split underneath.
How mounts fail
- Heat and oil. A leaking turbo oil line, a weeping valve cover or a spilled service fill softens the rubber from outside in. Oil-soaked mounts sag and then tear.
- Age. Rubber hardens. A hardened mount stops absorbing and starts transmitting, so the cab shakes more than it did last year without any single event you can point at.
- Overload. A machine that runs a breaker or works on steep ground puts far more cyclic load through the mounts than a machine digging level trenches.
- Bonding failure. The rubber separates from the steel plate. This is the dangerous one, because the mount can look intact while carrying no load.
Symptoms, in the order we see them
| Symptom | What it points at |
|---|---|
| New vibration in the cab, worst at idle or at a particular engine speed | Hardened or collapsed mounts |
| Engine visibly rocks when the throttle is blipped | Mount no longer controlling movement — often a bonding failure |
| Exhaust flex joint or pipe cracking repeatedly | Excessive engine movement, not a bad exhaust part |
| Hoses, wiring harnesses or AC lines chafing near the engine | Engine moving more than the design allows |
| Bell housing or mounting bracket cracks | Late-stage — the frame is now taking the load the mounts should have |
How to check them
- Look, do not guess. With the engine stopped, inspect each mount for splits, oil soaking and rust staining from a cracked bond line. Bring a light; the underside is where they fail.
- Rock test. With the engine idling, watch the block. A small, even movement is normal. A sharp, irregular movement, or movement that increases as the engine warms up, is not.
- Check what is bolted to it. A cracked exhaust flex, a chafed harness or a broken bracket is evidence, and it points back at the mounts rather than at the part that broke.
- Replace as a set. Replacing one mount leaves the load shared unevenly; the new one takes more than its share and fails early.
Why it is not the engine
Vibration gets mistaken for an engine problem constantly. A rough idle is blamed on injectors, on compression, on the fuel system — and the actual cause is that a failed mount is letting the engine shake the machine in a way it never used to. Before spending money on the engine, spend ten minutes on the mounts. On a Kobelco SK200-8 with the HINO J05E, that order matters: the turbocharger on that engine (787873-5001S / VH241004631A) and its oil lines are the usual reason mounts get oil-soaked in the first place, and a mount failure and a weeping turbo line are often the same job.
Before you order
Engine mounts are model- and generation-specific, and the rubber compound differs by position, so a mount that fits one side of one model is not a universal part. Send the machine model, the serial number and a photograph of the mount showing its shape and any number cast into the metal, and we will match it. We keep 3,000+ part types on the shelf in Guangzhou, with 100,000+ part numbers available to order, and every quotation states whether the item is genuine, OEM or aftermarket. We are an independent supplier of Kobelco parts and not an authorized Kobelco dealer.