An oil-impregnated sintered bush only delivers its low-friction, maintenance-free life if it is fitted correctly. The material is porous and comparatively soft, and it changes dimension when pressed home, so the handling that suits a solid machined-bronze bush is not always right here. The steps below apply across the Bushingo range — cylindrical and flanged, in BP25 bronze, FP20 iron and SO16 — and follow general practice for ISO 2795 sintered bushes.
Prepare the housing
Sintered bushes are retained purely by interference, so the housing bore does the work. Machine it clean, round and to the recommended tolerance — an H7 housing bore against the bush outside diameter is the usual starting point — and add a small lead-in chamfer, typically 15–30°, to guide the bush in. The bore must be square to the shaft axis; a cocked housing bore cocks the bush and causes edge loading.
Press, don't hammer
Always insert with an arbor press or a screw-actuated tool and a piloted mandrel matched to the bore. Hammering distorts the thin porous wall, closes the pores and can chip the ends. The mandrel should carry the bush squarely and stop flush. On a flanged bush, press only until the flange seats fully and evenly against the housing face — that flange is the axial location and thrust surface, so it must bed flat with no gap. Never press on the flange alone.
Allow for close-in and size the bore
When a sintered bush is pressed into an interference fit, the bore closes down — the thinner the wall and the greater the interference, the more it shrinks. Do not correct this by reaming: a cutting tool smears the bore and seals the pores. Instead, push a sizing pin — a hardened ball or plug slightly larger than the required bore — through the bush after fitting. This cold-works the bore to final size, restores a smooth porous surface and sets the running clearance in one operation. Take the finished running clearance from the size chart for the pairing rather than assuming a machined-bush value; it is generally a few hundredths of a millimetre and should never be run tight.
Shaft and clearance
The shaft is half of the bearing. A ground, hardened shaft with a fine finish (typically Ra 0.4–0.8 µm) forms and holds the hydrodynamic oil film far better than a soft, rough one. In service, shaft rotation and frictional heat expand the impregnated oil and draw it out of the pores to build that film; when motion stops and the part cools, capillary action pulls the oil back in. Adequate clearance is essential for this cycle — too little starves the film and overheats the bush.
Keep the pores open
The impregnated oil is the lubricant, and the bush is designed to run without added grease. Packing the assembly with heavy grease can bridge the pores and actually block oil release; if a supplementary lubricant is unavoidable, keep it light and compatible. Do not wipe or degrease the bore before fitting, and store bushes clean and boxed so grit does not embed in the soft surface.
First run
Expect a short bedding-in period during which friction settles as the film establishes. Sintered bronze of this type typically runs to around 100 °C continuously; if the assembly runs hotter than the material class allows, check clearance, alignment and load before blaming the bearing. Treat that temperature as a characteristic of the material, not as a certified limit for a given size.