Gallery, Projects and General > How do I??

How to change grease on sealed bearings?

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Groundhog:
A common mistake is to over pack bearings with grease. The manufacturer will usually publish the proper amount of grease for a particular bearing.

For a general rule of thumb (from a SKF web site);

"Super-precision bearings operating at high speeds should have less than 30% of the free space in the bearings filled with grease...
Open angular contact thrust ball bearings for screw drives should be lubricated with a grease quantity that fills ~ 25 to 35% of the free space in the bearing...
Sealed bearings are filled with a high grade, low viscosity grease that fills ~ 15% of the free space in the bearing. They are considered to be relubrication-free under normal operating conditions..."

If packed with too much grease they will run hot (not enough room for the balls to rotate freely).

hermetic:
 Yes, you can easily remove the seals with a sharp point like a compass or jewellers screwdriver.. Sorry, but regardless of what the manufacturers say, I don't go for underfilling bearings. On electric motors, in the day when  they had grease nipples, we would clean the nipple, remove a plug from the lower part of the bearing housing, and pump with grease to force out all the old grease, and keep poumping till new grease appeared at the plug hole. This meant that due to the design of the bearing housing, the bearing was 100% full. . Brook motors used SKF bearings, and these were fitted as new equipment. We never had a bearing failure unless the grease was the wrong grade, or contaminated. Some of the motors I rebuilt had done 35 years operating in the clean conditions of a powdered milk plant, and even after this extended life, which included daily maintenance, the bearings were still servicable. Less grease = more sales!! The sealed for life bearing usually has a life of 5 years or less!

Doc:
  I totally agree. I have a side business rebuilding electric motors,alternators and starters . And I never let a job go out of the shop without filling the bearings. Just remove seal and fill with a good quality grease and replace seal. I have never had a job come back where any f my bearings have failed. (just saying) My father-in-law owned the business before me and I bought it from him as a little side line cash generator and he will say the same and he was in the line of work for 60+ years! So I'll trust him and continue to do the same.

petertheterrible:
Probably not pertaining to your problem.  Had obsolete water-cooled engine with cooling fan on a stub-axle, identified a whine one morning when checking oil.  The whine turned out being a double roller with shaft, that had metal seals.  Being in a hurry to get the machine up and running (grader), I took the bearing (still in casting and being imperial) and boiled it in some grease, not the synthetic grade after I cleaned it with a cloth.  The bearing saturated with grease and lasted until the replacement arrived.

chipenter:
Had the repair a 1/2" Router today bottom bearing screeming , took it apart to get the size of the bearing , poped the seal no grease but some sticky dust , cleaned and filled with grease jobs a good un , I was going to buy a new bearing .

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