From: dcchan@engin.umich.edu (David Chi Wei Chan)
Subject: FAQ: Bearing maintenance
Date: Wed, 19 Aug 92 13:32:56 EDT
Organization: University of Michigan Engineering, Ann Arbor

                       THE BEARING MAINTENANCE FILE
                       ----------------------------
                           (written May 2, 1992)
                         (last changed May 23, 1992)
                      Compiled and edited by Tony Chen

Contents:
* General Info
* Sealed or Shielded?
* Bearing ratings
* How to maintain your bearings
  1st method : If you don't mind taking off the seals.
  2nd method : If you don't want to pry off the seals.


GENERAL INFO

Inline skates all use 608 bearings.  The number means that the bearings
are from the 600 series, with a 8mm inner diameter (the width of the
hole).  The "6" appears to be for the 6mm difference between the inner and 
outer radii (from the outside edge to the edge of the hole).

608 bearings are also the standard size for skateboard bearings.  If your 
bearings have letters following the "608" (like "S", "Z", or even "ZZ" or 
"SS") it is the manufacturer's way of denoting sealed or perhaps double 
shielded bearings.  To make sure what they mean you should probably
check with the manufacturer, since it varies from company to company.

Bearings for inlines generally come grease filled.  Some bearings like 
GMNs are sold either greased or oiled (but usually greased). 


SEALED OR SHIELDED?

There are basically two types of bearings.  Most likely you will have 
SHIELDED bearings, which most stock skates come with.  Shields will make
it hard for dirt and grime to get in, but they certainly aren't dust or 
water tight.

There are also SEALED bearings, which have a teflon or rubber lip seal that
actually touches the brace, and come packed with a fairly heavy grease.  
Rollerblade sells sealed bearings under the name Max Trainers.  You may find 
other brands as well.  The advantage is that they should last a long time 
without any maintenance at all.  The trade-off is that these bearings 
generally cost more and you also encounter a much higher rolling resistance.
Slower bearings are not necessarily bad, since many people like the added 
resistance for a better workout.


BEARING RATINGS

Bearings are rated on the ABEC [stands for?] scale.  NMBs are rated
ABEC-1, GMNs are ABEC-3, and Powell Swiss and Fafnir are ABEC-5.  Buying 
bearings rated any higher than ABEC-5 will probably not do any good 
since they aren't be meant for use in inlines.  The higher precision will
be lost to contaminating dust and dirt anyway.   (If it's a lot of speed 
you want, you should probably try cutting down wind-resistance instead.)

Really precise bearings are only used in high speed (read rotation) 
applications, as in machinery.  The next higher grade up from inline
bearings are in machines which are rotating at speeds of at least
10,000 rpm which is around 80+ mph.  You probably won't want to go that 
fast on your skates 8-)  At 50,000 rpm you would be traveling 400+ mph.
So which happens first?  the wheels melting, or the skin ripping off the 
skater?  Gives new meaning to shredding.


WHEN TO CLEAN AND RE-LUBRICATE YOUR BEARINGS

Exposure to dirt and water are the main reason that your bearings slow
down.  Bad bearings will be the ones which don't let your wheels spin
for a respectable amount of time.   Also, if you hear or feel the vibrations 
of metal rubbing on metal, chances are, your bearings are in need of some 
maintenance.

If some of the balls or bearing surfaces have become roughened, there's
basically nothing you can do.  They won't get any better, but they may 
last a long time anyway.  You can always replace your bearings a few 
at a time.

Take care of your bearings by cleaning and preping them as needed.  Assuming 
normal usage, they should last through several sets of wheels, depending on 
how much skating you do.


REPLACING YOUR BEARINGS
You can replace your bearings if (1) any of your bearings have somehow 
stopped spinning well, despite all the cleaning you do or (2) you want to 
change to different types of bearings (racing or sealed or whatever).


HOW TO TAKE CARE OF YOUR BEARINGS

1. Remove your wheels from the skates, and push the bearings out with a
   spare bushing (the plastic/metal part that goes between the bearings) 
   or one of the several types of bearing tools available on the market.


2. If you have Powell Swiss (Bones) bearings, simply pry off the removable
   plastic cap on each bearing.  If you have NMBs, GMNs (Germans), other 
   shielded bearings, or sealed bearings, carefully puncture or pry off the 
   shield (or seal) on one side. (Some people tell you to never pry off a 
   seal, some say it's okay.  It's really up to you.  whatever you do,
   lubrication always helps) 

   When removing the covers of entire sets of bearings at once, be careful to 
   only take off one cover per bearing.  Otherwise you'll be left with a 
   shieldless/sealless bearing (which won't last long against outdoor 
   conditions).

   Once you have the cover off, you should be able to see the ball bearings 
   inside, held in place by a brace.  You won't need the old metal covers 
   anymore.  In Bones bearings the cap is ALSO the brace, so you won't
   see a brace.  Bones bearings users should obviously keep the plastic cap
   when reassembling their bearings.

   You don't want to take the ball bearings out since they aren't meant to 
   be dismantled and reassembled.


3. Soak the bearings in paint thinner, naphtha, Simple Green*, or any
   other handy solvent.  In any case, the choice of solvent isn't crucial
   so long as you can get all the dirt and old grease cleaned out.  

   Avoid low-flash point solvents like gasoline, xylene, lacquer thinner, 
   etc. which are dangerously flammable.  Also wear latex/chem lab gloves 
   if possible.  Solvents are no fun to ingest or absorb through your skin.
   An alternative is to use a pair of tongs or tweezers to handle your
   bearings.

   How long you soak depends on how dirty and dried out your bearings
   have gotten.  Previously maintained bearings won't need to soak very
   long.  Bearings that have gone dry and have lots of grit in them may 
   need to soak overnight, or even several days.

   If necessary use a brush or swirl your bearings around in your container 
   to make sure everything breaks loose.  Small coffee cans, peanut jars, or 
   even the little black film canisters you get with new film, all make 
   decent containers.  You don't really need large amounts of solvent.  Just
   enough to immerse your bearings.  You also don't need to refill with 
   clean solvent with each bearing, unless the solvent you were using has 
   gotten really dirty.  The essential thing is that the dirt and grease
   is broken up.  Step 4 will remove most of the gunk.
   
   WD-40 is generally not recommended as a solvent since it leaves a sticky,
   dust attracting film on the bearings.

   *Simple Green.  Just soak the parts in pure Simple Green and rinse with 
   water.  Thoroughly dry everything off and lubricate immediately.  Simple 
   Green is water soluble, so take care to dry it well, since it can cause 
   rust otherwise.

   Parts come out much cleaner and much faster than with other solvents. 
   You should stay cleaner and there are no nasty fumes to inhale.  Simple 
   Green should be available in most grocery stores.


4. Now rinse out your bearings with hot, soapy water to make sure you clear 
   out all the solvent.  You now have some clean bearings.

   Clean, unlubricated bearings appear to have the lowest amount of unloaded 
   friction, but don't expect them to last very long if you skate on them.
   After a fairly short time, the surface of the balls will start to flake 
   and roughen and they won't spin very well.


5. Use a hair dryer or just air/sun dry to make sure that all traces of 
   water are gone.  Using a hair dryer or basking in the sun also preps the 
   bearing nicely by heating the metal somewhat.


6. Now lubricate with your favorite lubricant.  You can use Tri-flow or one 
   of the specialty lubricants distributed for bearings.  Bones bearings come 
   with their own Speed Cream.

   You can use grease or oil as you prefer.  Oiled bearings have slightly 
   less resistance, but need to be maintained more often (as often as
   once a week).  It is very helpful to have a little hypodermic style oiler 
   with a long needle to let you put the oil right where you want it.

   Grease works well because after a while most of it gets shoved out of
   contact with the balls and only a little bit smears onto the workings.
   However, newly greased (or heavy oil) bearings, will take a while to 
   expel any extra grease and move the rest out of the way. 

   For oiling, light oil, like sewing machine oil, or 5W-20 motor oil is a 
   good choice.  Household oils (3-in-one, etc) may gum up after a while and 
   the teflon-based lubricants have little particles of teflon that are only 
   in the way.  

   Let the bearings sit for an hour, and wipe them off.


7. Put one bearing back into the  wheel, with the open face towards the 
   inside of the wheel.  Insert the bushing and then put on the second 
   bearing (with the open face towards the inside again).  It is pretty 
   hard for contaminants to get into the bearings from the inside.


2ND METHOD (for keeping the shields on):

   First do Step 1 (from 1st Method).

   If your bearings are permanently sealed (or you don't want to remove
   the seals) you can still soak in solvent (see step 3) for several hours 
   or as long as you feel necessary.  Enough solvent should soak through to 
   remove some of the grease.

   Then you can lubricate the seams and/or press some in with your fingers.  
   Enough oil should seep through to lubricate your bearings (see step 6).

Compilation Copyright 1992 by Anthony D. Chen.  All rights Reserved.  
License is hereby granted to republish on electronic media for which no 
fees are charged, so long as the text of this copyright notice and license 
are attached intact to any and all republished portion or portions.

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