What is an Engine Cushion?
An engine cushion (also called an engine mount, engine anti-vibration mount, or engine isolator) is a bonded rubber-to-metal component that connects the engine to the equipment frame or baseplate. Its primary functions are:
- Vibration Isolation: Prevents engine firing forces and imbalance from transmitting into the chassis structure
- Noise Reduction: Reduces structure-borne noise in the operator cab and equipment enclosure
- Shock Absorption: Protects against transient shock loads during engine start-up, stall, and bucket impact
- Static Support: Carries the engine weight under gravity, including dynamic load factors
Shore Hardness and Stiffness Selection
The most important parameter for engine cushion selection is Shore A hardness, which directly determines the mount stiffness and natural frequency:
| Shore A Hardness | Application | Natural Frequency |
|---|
| 35–45 Shore A | Light machinery, generators, HVAC | 6–10 Hz |
| 50–60 Shore A | Excavators, bulldozers, construction equipment | 10–16 Hz |
| 60–70 Shore A | Mining equipment, large generators, marine engines | 16–22 Hz |
| 70–75 Shore A | Heavy industrial, high-shock applications | 20–28 Hz |
For effective vibration isolation, the engine cushion natural frequency should be at least 40% below the lowest engine excitation frequency. For a diesel running at 1,200 RPM idle (20 Hz primary excitation), the mount natural frequency should be below 14 Hz — corresponding to a 45–55 Shore A compound in a standard excavator engine mount geometry.
Rubber Compound Types for Engine Cushions
The compound choice determines chemical and thermal resistance:
- Natural Rubber (NR): Best resilience and lowest heat build-up. Standard for most excavator and construction equipment engine cushions including 1524771, 17A-54-46120, and 211-4987.
- SBR (Styrene-Butadiene): Improved abrasion resistance at lower cost. Used in blends for applications with sliding contact.
- EPDM: Superior ozone, UV, and heat ageing resistance. Recommended for engine compartments operating above 100°C.
- Neoprene (CR): Good oil and fuel resistance. Used in engine mounts exposed to oil contamination from leaking seals.
- NBR (Nitrile): Excellent oil and fuel resistance. Specified for environments with heavy oil contamination.
OEM Cross-Reference for Common Excavator Engine Cushions
Using the correct OEM part number ensures dimensional compatibility. Key part numbers by brand:
- Hitachi: 1524771, 6129902, 6180100, 1487116, 450122, 8A31-54-1110
- Komatsu: 17A-54-46120, 17A-54-46130, 195-54-78412, 56B-50-12315, 56D-50-12314
- Caterpillar: 211-4987, 227-0172, 358-0286
