Fit bearings correctly and double the life of your machine

Always prepare the area and the tools first

The fitting area should be clean and dry, away from grinding or welding that throws off metal particles. The tools you want are a vernier or micrometer, a fitting sleeve, an induction heater and heat-resistant gloves. Do not open the bearing packaging until you are genuinely ready to fit it.

Measure the shaft and the housing

Measure the shaft and the housing bore in at least two positions at right angles to each other, to check for ovality and wear, and compare them against the manufacturer's tolerances. As a rule the rotating ring — usually the inner — is an interference fit, while the stationary ring is a transition to slightly loose fit.

Cold pressing (for small bearings)

Use a fitting sleeve that touches only the ring being pressed on, and never drive force through the rolling elements. To press on the inner ring, use a sleeve that matches the inner ring; to press both rings at once, use a sleeve that contacts both. Tap gently and evenly all the way round.

Heat mounting (for medium and large bearings)

Heat the bearing with an induction heater or in a bath of clean oil to roughly 80–90 degrees Celsius above the shaft temperature, but never above 120 degrees Celsius, which changes the structure of the steel and reduces its hardness. Slide it onto the shaft right up to the shoulder straight away and hold it there until it has cooled.

Use the right amount of grease

Fill the free space inside the bearing itself, but fill the housing to only 30–50% of its free volume for normal speeds, and 20–30% for high speeds. Too much grease is one of the leading causes of abnormally high temperatures after a repair.

Check it after fitting

Turn the shaft by hand and listen for unusual noise or stiffness, then run the machine gently and measure the temperature at the housing surface. Normally it rises at first and then settles. If the temperature keeps climbing, stop the machine and investigate immediately.