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Assume I have a couple of closed bearings on some pivots on my bicycle.

These bearings:

  • are fitted on a housing
  • have an axle going through them
  • are tightened by bolts which also have cups to "protect" the black plastic part of the closed bearing

My question is, would you use grease between that black plastic part and the axle cup to protect the bearing from water and dust? I'm talking about a lot of waterproof grease which upon bolt tightening will overflow. Of course I will wipe out any excess after tightening.

I'm asking because even if the bearings are of high quality, I will sometimes find that dust or other small particles have entered its inside area making the bearing lose its smoothness and eventually making it wear faster. So, could that extra grease on the outside act as protection?

Edit: This question doesn't regard greasing inside the bearing. I'm asking whether puting grease on the bearing, covering the metal and the black part, will prevent water and dust from entering.

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5 Answers 5

Generally speaking, that style of bearing ("sealed cartridge bearing") is "permanently lubricated". You do not lubricate them and you replace the entire assembly if anything goes wrong with them.

A few people have claimed success by gently prying back the flexible gasket and injecting grease with a syringe, but these claims are subject to legitimate skepticism.

Note that the inside diameter and the outside diameter are not supposed to move relative to the external parts that hold them. If they are slipping it indicates that the "holders" are not tight enough or the bearing is failing and needs to be replaced.

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Shagging around with the plastic cap is likely to deform it, letting in more dust and water, therefore doing more damage than leaving it alone. –  mattnz Apr 10 '13 at 21:52
    
@mattnz - I agree, which is one of several reasons for the skepticism. –  Daniel R Hicks Apr 10 '13 at 22:19
    
(Though on earlier cartridges the gasket was fairly flexible neoprene. Newer ones no doubt use a stiffer plastic.) –  Daniel R Hicks Apr 10 '13 at 22:20
    
I've discovered a few super cheap bits that pass as "sealed" bearings, but the dust seal does little in the way of sealing. The covers on these come off quite readily and you can relube them, but they're not high quality bearings in the first place. Mostly, they're in the cheap/generic parts from China category, but they do exist. –  WTHarper Apr 12 '13 at 3:17
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In addition to other answers, shagging around with the plastic cap is also likely to deform it, letting in more dust and water. This is likely to counter any benefit of getting extra grease into it, therefore doing more damage than leaving it alone.

These bearings are (should be) cheap - they are designed as long life, no maintenance but throw away item - use them how they were designed. Shop around - you don't need to get them from the LBS at Bike Shop prices - its not uncommon to go to bearing specialist and get an identical part for 10th of the price of the branded one. I would be surprised if you went though one set, and stunned if you went though more than a couple of sets in the life of the bike.

If you really feel compelled to maintain them, the best option is go down to a local bearing supplier, and get identical size open bearings which to can be easily striped and cleaned whenever you feel the inclination, (but at least once a month).

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I would take exception to sealed bearings being "cheap". Phil Wood made his name selling hubs containing industrial-grade sealed bearings, and they have a reputation for greatly outlasting conventional bearings, especially in dirty conditions. The main negative is that they are heavier, plus, when they do wear out they need to be "pulled" and replaced, vs simply serviced. –  Daniel R Hicks Apr 12 '13 at 11:16
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The black plastic part that you are referring to is the dust cover. It is there to protect the bearing from dust and contaminants. You do not need to protect the dust cover from dust :-)

In general, you will not need to do anything to a cartridge style bearing. In fact, a high viscosity grease on the outside of the bearing will likely cause more dust to stick, shortening the life of your bearings. You can try injecting some low viscosity oil, but you're unlikely to get much into the bearing without removing the dust cap. If you do remove the dustcap, you probably won't get it back on perfectly, again making it more susceptible to dust.

If it feels like it is getting gritty, it's time to replace it. As some other users have already pointed out, you will find the best prices and selection of cartridge bearings at a bearing supplier. If you like to kick it old-skool, look for "bearing supply" in the yellow pages. If you are hip with the new-fangled tech gizmos, then log onto maps.google.com and search for "bearing supply." Whatever butters your muffin.

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Amazing - a word for word replication of my answer, yet yours get +1 and mine gets -1. Is it "butters your muffin" tickled someone fancy, or my "shagging around" offended someone. :) –  mattnz Apr 12 '13 at 4:30
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I spent many years skateboarding before jumping on a bike and bearing maintenance (for identical bearings) was pretty key to making expensive bearings last much longer. I never used anything to waterproof the bearings from the outside (or heard of anyone who did) but took time to do regular maintenance. Guys with far lower mechanical skills than those who wrench bikes could do this stuff easily.

You can remove the dust shield quite easily (some are held in by a split ring others just prise out) but you need to be careful. Once open remove the balls and retainer and clean them with a solvent based cleaner that doesn't leave a residue (so not WD40). Clean up the races and put all back together. Re-lube with a decent non dust attracting oil, I used to use sewing machine oil but now would just use a decent chain lube. Wipe down the shield replace it carefully and clean the outside of the bearing up to remove any lube residue. Place back on the axle dry and let the balls do their work.

One problem with buying generic bearings to replace OEM ones is ensuring that they have similar properties to withstand impact and side loading forces. Most industrial bearings are designed and manufactured to spin in place at very high speeds with consistent external forces. You may get a good deal on the bearing but you'll likely have to replace them more often as they could fail significantly faster.

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I would not use a grease for this type of bearing. The grease will stick to the sides and will attract dust and dirt.

Instead, I'd use a regular bearing oil to oil it. Usually it is somewhat liquid and the excess of it would just go away after the "greasing". In Europe one can get the oil from Bosch (for example). I suppose in other parts of the world there are other types of companies specializing in this. But oiling is not your question, is it?

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