Pillow Block Bearing Installation
Checklist for mounting UCP and UCF units: shaft prep, alignment, mounting bolt torque, set screw tightening, grease nipple position and first-run checks.
Mounting a pillow block (UCP) or flange (UCF) unit is straightforward, but a few steps are easy to do in the wrong order. This checklist covers shaft preparation through to the first run.
Before mounting
- Shaft diameter matches the insert bore (see shaft size to mounted bearing selector if unsure).
- Shaft surface is clean, free of burrs and rust at the mounting position.
- Mounting surface is flat; shimming an uneven surface can distort the housing and bind the bearing.
- Bolt holes in the frame match the housing’s bolt spacing and bolt size.
Mounting the unit
- Slide the unit onto the shaft to its mounting position.
- Fit the mounting bolts loosely first, then align the housing before tightening fully.
- Tighten mounting bolts to the torque the bearing supplier gives for the housing, in a criss-cross pattern on four-bolt housings. A cast iron foot can crack below the value a bolt torque chart gives for the bolt size.
- Rotate the shaft by hand to seat the first set screw before tightening the second.
- Tighten both set screws to the same torque; do not leave one looser than the other.
- Check the grease nipple is accessible and not pointing where it will collect water or debris.
Mounting bolt torque: ask for the housing figure
A bolt torque chart tells you what the bolt can take. It does not tell you what the cast iron foot of the housing can take. On a pillow block, the cast iron foot can fail first, so ask the bearing supplier for a tested torque for that housing and bolt size.
We learned this on an order. In 2017 a customer in Chile asked us, before shipment, for the mounting torque of P208 cast iron housings with M14 bolts (the housing of a UCP208 unit). In more than ten years of exporting, no customer had asked us for this figure before. We bought a torque wrench and tested 20 units from the shipment. No bolt hole cracked at up to 20 N·m, so we gave the customer “not more than 20 N·m”.
On site, the crew tightened every bolt to no more than 20 N·m, and more than 5 in 100 housings cracked at the bolt holes. We never found out whether our torque wrench read differently from theirs, or whether our test method was wrong. The customer sent us photos, and we air-freighted the same quantity of units again, free of charge.
What we do now:
- Test more samples before giving a torque figure.
- Give a figure with a margin below the tested value. For P208 housings with M14 bolts, we now give 18 N·m, and we have moved to a better cast iron housing.
- On site, use a calibrated torque wrench and check the mounting surface is flat before tightening. A foot that bridges a gap bends as the bolt pulls it down.
If your installation contract asks for a mounting torque, put the housing designation and bolt size in the inquiry, and we will state the figure for that housing.
Alignment and first run
- For units supporting both ends of a shaft, check the two housings are in line before final tightening — a pillow block has some self-aligning capacity in the insert, but it does not correct gross misalignment between housings.
- Rotate the shaft by hand through a full turn; it should turn freely with no tight spots.
- Add grease if the unit was shipped dry or has been stored for an extended period.
- Run the machine briefly under no load and check for unusual noise, heat or vibration before putting it into service.
See pillow block bearing identification checklist if you need to confirm the size before ordering a replacement, or send the application and shaft size to sales@fuli-bearings.com for a quotation.
FAQ
In what order should the set screws be tightened?
Tighten the first set screw, rotate the shaft by hand to seat it, then tighten the second set screw to the same torque. Tightening both before rotating the shaft can leave the insert cocked slightly on the shaft.
Which way should the grease nipple point?
Wherever it stays reachable for regreasing and will not collect water or debris — commonly up or to the side, not pointing straight down. Confirm the housing can be rotated on the insert before locking the set screws, since the nipple position is set before final tightening on some housing styles.
Why run the shaft by hand before starting the motor?
Rotating the shaft by hand after mounting catches a misaligned bore, a bent shaft or an over-tight set screw before the motor is under load. A unit that turns stiffly by hand will not free up once running.
What torque should I use on pillow block mounting bolts?
Use the figure the bearing supplier gives for that housing, not only the bolt torque chart value for the bolt size. A cast iron housing foot can crack well below what the bolt can take. For P208 cast iron housings with M14 bolts, FULI gives 18 N·m.