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Installing a tight bearing on a shaft


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This is a question that that has several variables and can change the actual prcedures.

1)Measure the internal diameter (ID) of the bearing and outside diameter (OD) of the shaft. Subtracting the ID from the OD gives the press fit.
Go to the bearing supplier's website and verify the press fit is within the limits the specified. If the press fit is too tight the bearing may split or may run to tight do to expansion of the inner race. If it is too loose it may run not stay in place on the shaft and may even "whallow" looser totally ruining the shaft. Some specifications may include a force in pounds required to push the bearing on the shaft. Loc-tite and its competitors have products that can secure the bearing to the shaft if it is not too loose

If specifications can not be found for the specific bearing find one that is close to the same dimensions and use these specifications.

2)There are 3 ways to install a tight bearing

2.1) On small bearings a press can be used to force the bearing on. Use care and pushing the bearings. Some hydraulic presses have pressure gages that allow the force the the press is putting on the bearing can be directly read. Make certain the force of the press is resisted by the inner race of the bearing and the shaft. Make certain that there is no pressure on the outer race as this will damage the bearing, as this axial force can not be sustained by the bearing. The press can be used for larger bearings but when bearings get large 4"-6" ID or more, heating becomes more and more viable

2.2) On larger bearings they are often heated with electric bearing heaters or heated oil baths. We blacksmiths can use my favorite heat source, a toaster oven. Not only can we use it for heating our sandwich we can temper and heat bearings. Verify the maximun temperature for heating the bearing. Never heat above 275-300 deg F unless recommended by the bearing manufacturer. Do not heat bearings with plastic or rubber cages, shields or seals.

2.3) Cool shaft with dry ice. This is not commonly used, but is possible.

Nevr use a steel hammer to drive a bearing on or off. If you must use a hammer to drive a bearing use a brass drift or punch to drive the bearing. Bearings are "glass hard" and may shatter if struck with a steel hammer.

Once you get the feel for pressing on force fit bearings, some of these steps can be skipped based on experience.

I am not suggesting that I always measure the shaft and the bearings. With a small press and small bearings you can just very carefully press the bearings on. If they push too hard stop and examine for possible problems.

Use common sense and watch and think about what is happening.

Make sure that no force is exerted on the outer race of the bearing, when the inner race is pressed on the shaft or that no force is applied to the inner race when the outer race is pressed into a housing.

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We install "tight fit" bearings regularily at the train repair yard. We do alot of tight fit installs that are not bearings as well.

We do not freeze the shafts nor heat the bearings at all, although we do heat a stop plate prior to installation on the axle bearing install, but not the bearing itself.

We ensure the shafts are free of debris and high spots visually, any burs are emery clothed out. The bearings are pressed on with a hydraulic cylinder using slow but steady pressure, the shaft is dry although the inner portion of the bearing is coated with a thin layer of grease. The hydraulic pressure is being applied to the inner race of the bearing transfered though a properly machined sleeve.

That being said there is a gearbox bearing install that may be heated before install, I will have to ask the guy in charge of the rebuild area. I know he uses hydraulics as well to install but he may heat prior to that install.

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we warm the bearings in an oilbath.

Dont be to 'heroic' about the interferace fit - on most bearings .0005 - .001" is a suitable pinch. the shaft and inner race will always expand / contract at a very similar rate, so the pinch will never be lost.

Depends on the bearing and application though. more info needed for accurate, correct advice.

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