What can go wrong?
Fitting a bearing into a housing bore is a simple job when done properly, but alignment of the bearing to the bore is critical to prevent a cocking motion during insertion, which can damage or ruin the bearing or the housing (NHBB's installation guidance). Most damage comes from force going through the wrong place, from dirt, or from a crooked start.
How do you prepare?
- Keep it in its packing. Bearings and rod ends should stay in their original packaging until shortly before installation, so the preservative lasts as long as possible, and no foreign particles may be allowed into the outer ring during installation.
- Add a lead-in. The ends of pins and shafts and the edges of housing bores should have a lead chamfer of 10° to 20°. This makes it easier to press the bearing in and lowers the risk of skewing it and damaging the mating surfaces. A lead chamfer or radius on the bearing or housing is essential.
- Know your fits. See Q1-06. Interference between the ring and the housing, or the inner ring and the shaft, is what makes the bearing slide at the ball and not on the shaft or in the housing, but too much interference closes the clearance (Q1-07).
How do you push it in?
- Use a press and a tool. An arbor press or hydraulic press is the right tool; a hammer or any shock-inducing method should never be used. A guide pin holds the ball square (at 90°) while all the force is applied to the face of the outer ring only.
- Push on the ring that is going in. Apply force only to the ring being mounted: on the outer ring when pressing into a housing, on the inner ring when pressing onto a shaft. Never apply force through the sliding surfaces, because this damages the bearing and greatly shortens its life. Installation and removal forces must not be passed from the spherical shape to the bearing shells.
- If both rings are a press fit, make a special tool that presses both at once.
When do you use heat or cold?
When the fit is tight, a temperature difference makes the parts slide together with little force. Temperature-differential installation is the recommended method, and for a heavy interference fit it is a must, to prevent galling of the bearing or housing. After such a fit the bearing usually cannot be removed without galling damage, and the ball-to-race fit has to allow for the race shrinking, by up to the whole of the interference in some cases. Heat, refrigeration or adhesives may also be used; ask the maker. The right temperatures depend on the fit and the materials, so use the maker's figures.
How do you position and hold it?
- Split ring. If the outer ring is split, place the split at 90° to the main load direction, otherwise life is shorter, especially under heavy load. The lubrication holes then fall in the load zone (Q1-06).
- Retention. In hydraulic cylinder eyes, bearings are pressed in and either permanently fixed by flanging at several marks around the edge, or held by removable retaining rings. Whichever the design calls for, it keeps the outer ring from moving along the bore.
- Stay inside the tilt limit. The tilt angle in the maker's table must not be exceeded during mounting (Q1-05).
What else matters when pressing into a rod eye?
If the rod eye is welded, press the bearing in after the welding is finished and the eye has cooled: welding heat can ruin the bearing's heat treatment, so never fit the bearing and weld afterwards. The fits that cylinder standards specify sometimes differ from the fit the bearing maker recommends, and the radial clearance table in DIN ISO 12240-1 applies only to the recommended fit, so do not assume the nominal clearance still holds once the housing has squeezed the outer ring. Keep the press sleeve's bore clear of the ball and liner and push only on the outer ring's end face, and support the eye from the far side near the bore so it does not distort. A staked bearing is permanent, while a circlip-retained one can be taken out, which decides whether you can replace the bearing alone (K03-Q1-24).
What do you check afterwards?
- The ball turns freely, with no stiffness that was not there before.
- The bearing sits fully in the bore, and the retention is in place.
- The inner ring is clamped as the design intends: firmly, so it does not turn on the pin or shaft, but not so hard that it binds. Excessive clamping expands the ball and binds it in the race, while a ball that is not clamped lets the motion happen on the bore (K01-Q1-05).
- A bearing that needs grease gets its first lubrication as the maker describes (Q1-08).
What is different when fitting into a control arm, a tube end or a uniball cup?
The housing is usually thin-walled and soft: a tube end, a weld-in cup or an aluminium arm. Three things follow from that.
- Support the wall. Back the housing around the bore with a sleeve while pressing, so the press load does not bulge or ovalise it (the rod eye advice above applies). Push on the outer ring only.
- Weld first, press second. Welding a cup into a tube distorts the bore and heats the area; fit the bearing after the weld has cooled and the bore is finished.
- Check the whole joint after fitting. The retention (a staked lip or a retaining ring) is in place; the inner ring is clamped between spacers of the designed width and flatness, firmly but without binding the ball; the ball turns by hand through its full angle; the nipple faces somewhere reachable, away from road debris, and the hole meets the groove. Bolt torque and locking follow the vehicle designer's specification; do not use the bearing maker's clamping advice in place of it.
A staked bearing usually cannot be replaced without re-staking tooling, and a retaining-ring type can, which matters when the arm is the expensive part (Q1-14). For cup-housed formats see SYZ's uniball cups and uniball cup buyer's guide.