Upper & Lower Bushing Wear Limits: When to Replace?
26 November 2025
The hydraulic breaker tool (chisel) moves inside the bushings. These bushings keep the tool centered and ensure the piston strikes correctly. However, they wear out over time due to friction.
A Lower Bushing (Front Head Bushing) or Upper Bushing that is not replaced on time can lead to piston and cylinder damage costing thousands of dollars.
1. Bushing Types and Functions
HKM breakers typically have two or three types of bushings:
- Lower Bushing (Kafa Burcu): The main bushing at the bottom holding the tool. This part wears out the most. It faces dust and impact first.
- Upper Bushing (Merkezleme Burcu): Located higher up, it centers the upper part of the tool.
- Thrust Bushing (Şank Burcu): A special bushing found in some models that absorbs impact.
2. Wear Limit Table
If the gap between the bushing and tool exceeds a certain limit, the piston will break. Here are the replacement limits:
| Tool Diameter (mm) | Breaker Type | Max. Gap (Time to Replace) |
| 40 - 70 mm | Mini Series | 5 mm |
| 80 - 120 mm | Medium Series | 7 mm |
| 135 - 180 mm | Heavy Series | 10 mm |
3. Compatible Brands
Every breaker brand has different bushing dimensions. HKM stocks bushings for the following models:
- Atlas Copco (Epiroc): SB series, MB 1500, MB 1700, HB 2000, HB 2200.
- Rammer: S 25, S 27, S 29, E 68, G 80, G 100.
- Furukawa (FRD): F 22, F 27, F 35, F 45, FX Series.
- Montabert: SC 28, SC 36, V 1200, V 32.
- Soosan: SB 40, SB 50, SB 81, SB 121.
- Others: MSB, D&A, Daemo, Okada, Toku, DNB, MTB.