The Bearing Maintenance File

(written May 2, 1992)
(last changed Jan 6, 1995)
(updated Apr 56, 2003)

The standard inline skates bearings have the designation "608". The "608" means that the bearings are from the 600 series, with a 8mm inner diameter (the width of the hole, i.e., internal bore). 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. Quad skates use either type 608 (8mm internal bore) or type 627 (7mm internal bore). The 608's for quads are the outdoor 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. An "RS" label means shielded but that the shields are removeable (i.e., serviceable bearings). To make sure what they mean you should probably check with the manufacturer, since it can vary from company to company.

Lately, the inline industry has been using "688" bearings, which are micro bearings, to use in wheels with microhubs. The rationale behind this is to get some weight reduction in the wheel and bearings, while still having fairly low rolling resistance.

A little cross-reference on part numbers for bearings, the 7MM ones are for quality indoor skates, the 8MM ones are used for in-lines, other indoor skates and skateboards.

Double Shielded:

        NTN     Fafnir  MRC     ND      SKF     HCH     YW

7MM     627-ZZ  37KDD   37FF    77037   R7-2Z   627Z    60027

8MM     608-ZZ  38KDD   38FF    77038   R8-2Z

Double Sealed (neoprene rubber):

        NTN     Fafnir  MRC     ND      SKF

7MM     627-LL  37PP    37ZZ    99037   R7-2RS

8MM     608-LL  38PP    38ZZ    99038   R8-2RS

Single shielded/sealed bearings usually delete one of the doubled prefix/suffix characters. (Thanks go to George for the above chart).

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

Some of the bearing manufacturers are: Black Hole, Boca, Boss, Cyko, DF, Fafnir, FKD, Get Your Bearings, GMBH, GMN, Grizzly, Hyper, Kryptonics (Russian), M&A Smith Stealth, NHBB, NMB, Powell Swiss "Bones", RPM, Sonic, Terminator, Twincam and Yak. (The NMB's are common as a stock ABEC-1 bearing in production skates, but they also make ABEC-5's). There are many brands of bearings out on the market now, although you should know that some are just bearings from the same factory, just labeled differently. Some brands are NMB, Powell Swiss (commonly called Bones bearings), GMN, Fafnirs, Black-Hole, YAKs, Twin-cam, M&A Smith Stealth, (Super) Sonic, Terminator, Hyper (Boss & RPM), FKD, NHBB, GMBH, DF, Grizzly.

Sealed or Shielded?

There are basically two types of bearings: shielded vs sealed. Very likely you will have shielded bearings, which all stock skates come with (as far as I know). Shields make it hard for dirt and grime to get in, but they certainly aren't dust or watertight. For superior protection against the elemnts, you need sealed bearings.

There are three kinds of shielded bearings: 1) two shields (metal), 2) one metal shield & one pop-out cap for maintanence, 3) two pop-out caps. If you have types 2 or 3, you'll have an easier time re-lubing your bearings (see below)

Sealed bearings have a teflon or rubber lip seal that actually touches the race and come packed with a fairly heavy grease. These are quite impervious to dust or water. 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 ("Annular Bearing Engineering Council", annular means circular) scale. The higher the ABEC number, the greater the manufactured bearing precision. There are no required materials to meet the ABEC specifications. The bearings simply have to be made to a certain precision.

You may find cheaper skates with bearings not even rated on the ABEC scale (primarily on "toy" in-lines and real low-end/kids skates). These will often be labeled as semi-precision bearings.

In non-skating applications (like in industrial machinery) using higher ABEC-rated bearings lets machines meet particular mechanical tolerance or vibration levels, so they can operate at a high speed. This is not because there is less rolling resistance, but rather because the precision is better.

Whether ABEC-5 bearings will let you skate faster than ABEC-1 bearings is still largely debatable. The higher precision may not make a significant difference when you're at 10-20mph. Compare that with typical machinery that may run at 10,000 rpm (~80 mph), where the smallest change in precision can make a difference. Also, the higher precision will eventually deteriorate down to ABEC-3 or 1 due to dust, dirt and regular wear and tear. Cutting down wind-resistance and improving your technique is probably much more effective at increasing your skating speed.

However, all this is not to say that there is no reason to buy ABEC-3 or ABEC-5 bearings. Most ABEC-3 and 5 rated bearings are serviceable, while ABEC-1's typically are not. So although you may not be buying more speed, you will be getting more convenience in maintanence.

(see related article ABEC = HYPE?)

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 ones which don't let your wheels spin for a respectable amount of time (the definition of "respectable" depends on on your type of bearings). 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 probably want to replace some of your bearings if (1) any of them them 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

1st Method: Taking the shields off

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.
Now there's three types of situations you'll be in: a) If you have shielded bearings with pop-out caps (Powell Swiss or Black Hole brands), simply pry/pop out the plastic cap on each bearing.

b) If you have other serviceable bearings like Twin-cams or YAKs you need to pop out the snap rings (C-rings) before you take off the shields (use a small screwdriver to snap out the snap rings).

Shown below are a close-up of the C-ring and shield when you take them out. Notice that the C-ring has a diagonal edge at either end. There's really only one end that you can pry the ring out with (i.e., the end with the pointed edge towards the inside). In the picture, it would be the end at the top of the image. (Click on either image to see an enlarged version).

c) For non-serviceable bearings like NMBs, GMNs (Germans), or sealed bearings, FIRST make this decision: do you want to take the shields off?

Some people tell you to never pry off a shield/seal, some say it's okay. It's really up to you. In general, if you think you will be doing a lot of maintainence on your bearings, you are much better off taking the shields off. Whatever you do, the new lubrication always helps.

NOTE: if you have sealed bearings you might not want to pop the covers since you could ruin the seal integrity a little, which is what you're paying extra for in the first place. Still, I have some people say they put their bearings back together with no harm, so it is possible. For more nitty-gritty on maintaining sealed bearings, look at http://www.svi.org/~nates/bearing.html.

If you decide no then skip down to the section marked 2nd Method.

If you decide yes then carefully puncture or pry off the shield (or seal) on one side. Use a very small screwdriver, and pry along the edge of the shield until you can get under it and pop it off. If this is difficult, you can always push the screwdriver into the shield (or tap it through (lightly!) with a hammer or heavier tool). You don't need a whole lot of force since the shields aren't all that thick or hard.

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 retainer (click on the image for a close-up).

You won't need the old metal covers anymore so you can throw them away (assuming you're using non-serviceable bearings). They're no good anymore anyway since they're probably bent and warped from the removal.

In Bones bearings the cap is ALSO the brace, so you won't see a brace, but just 7 bearings rolling around. Bones users should obviously keep the plastic cap when reassembling their bearings.

NOTE: You don't want to take the ball bearings out since they aren't meant to be removed and replaced. Besides, you'll scuff the bearings and they won't roll well anymore.

Soak the bearings (c-rings and shields too if you've got serviceable bearings) in Simple Green or some other biodegradeable detergent. DON'T dilute with water! Use it straight from the bottle. The detergents are very cheap and you don't need a whole lot anyway (just enough to cover the bearings). If you want to speed things up a little, put your cleaning container in a larger container. Fill the area around the cleaning container with warm or hot water but not enough to spill over into the cleaning container.

The choice of cleaner/solvent isn't crucial so long as you can get all the dirt and old grease cleaned out. However, I'd highly suggest using one of the biodegradeable cleaners. They're cheaper, safer, easy to dispose of (just let it go down the sink) and good for other cleanup tasks as well.

If you do insist on using solvents, avoid low-flash point solvents like gasoline, xylene, lacquer thinner, etc. which are dangerously flammable. Also wear latex/chem lab gloves if possible when handling these chemicals. 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.

Soaking the 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 those little black film canisters, all make decent containers. Dave Woodall (woodall@adrs1.dseg.ti.com) has his own way of swirling. He uses a battery operated drink mixer and spins his bearings to cleanliness. He says it works really fast, so if you like, try it out 8-)

You don't really need large amounts of cleaner or 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 cleaner since it leaves a sticky, dust attracting film on the bearings. Note, however, that some people swear by WD-40. It has become somewhat of a heavily-debated topic, so experiment with it if you'd like.

Ultrasonic cleaners are ideal for cleaning bearings. If you have access to one, you can clean your bearings en mass and avoid getting your hands dirty.

Now rinse out your bearings with hot, soapy water to make sure you clear out all the solvent. You now have some clean bearings. If they're truly clean they ought to spin real fast.
Use a hair dryer to make sure that all traces of water are gone.
Now lubricate with your favorite lubricant. Lubricant choice always seem to be somewhat preferential. Lots of people find one lube that works for them and they just stick with it. It's hard to try out multiple lubricants and get a thoroughly accurate comparison throughout all types of skating conditions. 1) people don't always have the extra money to do so, 2) to change lubes you need to clean and relube (unless you have an extra set of bearings) and 3) there's still no real good way to measure how well a lube helps speed up or slow down your skating. A no-load "finger-flick" spin test doesn't really cut it since it doesn't entirely translate into the equivalent rolling resistance with your weight on it.

Ideally, you'd have an indoor incline and/or flat surface, multiple sets of identical bearings for each lube, and you'd see which one gave you the most glide. Of course, this still doesn't take into account how fast the lube dries or bleeds from the bearings, or how easily it collects or repels dust/grime/water, and on and on.

In the end, it doesn't make a huge difference unless you're into serious racing. Your main choice will be choosing between oil, cream/grease, telfon based lubes, (bicycle) wax/paraffin, and whatever else is out there. Most people end up using grease or oil. 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 bearings, will take a while to expel any extra grease and move the rest out of the way.

For oils, although you can use stuff like sewing machine oil, or 5W-20 motor oil, household oils (3-in-one, etc) may gum up after a while. In any case, most mail-order shops sell their own brand of lubricant, as do many of the bearing manufacturers (e.g., Bones and BlackHole). Although it's not proven these "special" formulas are all that better, it's usually only a few bucks for a nice little bottle of lube that should last you for a long time. Some brands also come in a very handy hypodermic-style dispenser which is perfect for putting a drop exactly where you want it.

NOTE: Use only a few drops of oil per bearing! Overlubing will not only waste your lube, but you'll also make the bearings more sticky and more prone to attracting dust and grime, which is exactly what you don't want. Spin the bearing to spread the oil around inside.

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

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: 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).

3rd Method (The Bont Method)

From Bont's web site:

Secret Lubrication Technique:

Wash the bearings in petrol and two stroke oil at approximately 50:1 ratio. Take the bearings out and shake dry. Place them on a clean dry cloth or paper towel. When all the petrol has evaporated, reinstall the bearings without adding any further lubrication. Your baby bonts will go even faster! This should be repeated every few days to a week or when they start to feel dry. This technique can be used on all bearings. This works far better than all the speed lubes you spend your $ on.

*All images copyrighted © 1992-2003 by Anthony D. Chen. Permission is granted to use this logo in World Wide Web HTML files so long as this copyright notice is included as either an HTML comment alongside the invokation (IMG SRC or HREF or otherwise) of the logo, or in the visible text.

The image may not be sold for profit, nor incorporated in commercial documents or merchandise without prior written permission of the copyright holder.