CAT 521-9878 BUSHING–SEM

CAT 521-9878 (5219878) is a Caterpillar original SEM bushing, adapted for the articulation structure of SEM series loaders and other equipment, used to support pins and reduce wear and provide positioning. The following is purely precise information (no additional description): Cat®…

Core Parameters and Information

Item Details
Part Model: CAT 521-9878 SEM Bushing

Part Type: Radial support bushing for construction machinery, adapted for the hinge points of booms, rocker arms, connecting rods, etc., of SEM loaders, excavators, etc., bearing radial loads, absorbing impact vibrations, and reducing wear on pins and supports.

Material: 20CrMnTi alloy carburized steel, carburized layer depth 0.8-1.2 mm, surface hardening hardness HRC 58-62, core hardness HRC 30-35, surface phosphated for rust prevention and wear resistance.

Key Dimensions: Inner diameter 45.00 mm (1.7717 in), outer diameter… 60.00 mm (2.3622 in), total length 55.00 mm (2.1654 in), inner bore chamfer 1.5×45°, parallelism of both ends ≤0.015 mm

Structural Features: Straight cylindrical oil-groove-free structure with positioning steps at both ends, suitable for interference fit installation, used for radial support between the hinge pin and the bracket.

Compatible Structures: Loader boom – rocker arm hinge bushing, excavator stick – connecting rod hinge bushing, grader blade bracket hinge bushing.

Applicable Working Conditions: Suitable for -40℃ to 120℃, radial load ≤18 kN, suitable for low-speed swing (≤12 rpm) and intermittent impact conditions.

Compatible Models and Assemblies:
Loaders: SEM 655D, 656D, 660D, 665D (boom hinge assembly, rocker arm hinge assembly)
Excavators: SEM 210C, 215C (Stick articulation assembly, boom linkage articulation assembly)
Graders: SEM 919, 921 (Blade bracket articulation assembly, drawbar articulation assembly)
Compatible Assemblies: 521-9878 SEM bushing assembly, 306-2145 hydraulic pump assembly, 246-5211 engine fan assembly
Installation and Fitting Points:
The bushing and mounting hole should have an interference fit, with an interference amount of 0.018-0.028 mm. Press-fitting should be used, with a press-fitting pressure ≤90 kN. Do not hammer during installation.

Before installation, clean the inner hole of the bushing and the mounting hole, ensuring there are no burrs, oil stains, or rust. Check the carburized layer of the inner hole for peeling or cracks.

After installation, the bushing end face should be flush with the mounting surface, with a coaxiality ≤0.025 mm. The clearance between the pin and the bushing should be 0.025-0.045 mm, and there should be no jamming during swing. After installation, apply grease (CAT TO-4 grade) to the mating area between the bushing and the pin, and replenish it every 1000 working hours.