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Ball Bearings For Dummies.

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I'm wondering what to look for in buying ball bearings (wheel bearings, transmission, etc.) if you know the 4 digit number and want top quality bearings.  I see most listings describe them as "electric motor grade".   Are there different grades that are listed with the same 4 digit number?  I know the seals add a few letters to the number.  THAT I can figure out.   I see a HUGE difference in price from top to bottom.  Is it worth the premium?  Should I stick with US manufacturers?  They would be easier to find for me although I certainly think Japanese bearings are good quality.  Not too sure about Chinese bearings, though.

Any advice for me?

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Thanks, William.  Good reading.   Now, do seals have any kind of a numerical system or do they just go by dimensions?

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There are only about a dozen good bearing manufacturers in the world, a good bearing supplier will have several price points for each size and can make recommendations for your application.

Use the cheapest sealed bearing for the wheels because the failure mode is dirt not load.

Be careful on crank bearings because of running clearances, called "class" in bearing speak, take the bearings to the bearing supplier so they can verify the "class".

Moderate quality is all you need for other engine bearings.

There is a standard coding system for metric bearings based on a 4 digit number, along with prefix and suffix characters for special features like sealed, shield, etc. The code is usually along the rim of the outer race. Here is a list of some common standard metric bearings along with 3 specialty bearing (with 5 digit codes):

#........IDx ODx TH
6001.. 12x 28x 8
6201.. 12x 32x 10
16101 12x 32x 8
6301.. 12x 37x 12
16002.15x 32x 8
6002...15x 32x 9
6202.. 15x 35x 11
6302.. 15x 42x 13
6003.. 17x 35x 10
16003 17x 35x 8
6203.. 17x 40x 12
6303.. 17x 47x 14
6004.. 20x42x12
6204.. 20x 47x 14
6904.. 20x37x 9
6304.. 20x52x15
6006.. 30x55x13

60xx are light duty sizes. 61xx a little heavier, etc
The last digit is the ID code; 1=12mm, 2=15mm, 3=17mm, 4 and greater multiply by 5 for the ID.

Look up the bearings on the OEM part fiche, they will often have the metric bearing code in the part number (Suzuki) or the description (Honda).

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I agree with the warnings on mains.  When I need main bearings, I go OEM.

 

In some engines, like the YZF's, you don't have an option.  They have special machine work that ties in with the retainers, and aren't available in the aftermarket.  In other cases, there's no reason not to use aftermarket as long as you stay with good quality stuff like the major brands mentioned earlier, AND pay attention to the internal clearance on the OEM bearings.  This is generally marked with something like C3, C4, etc.:

 

http://www.bearingworks.com/technical_data/internal_clearance.php

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Honda often will customize a standard bearing; some crank bearings and steering head bearings are that way. 

Case in point are the 26x47mm tapered roller steering head bearings Honda has used since the 70s; they are based on a metric 32005 bearing (25x47) with a 1mm larger ID.  So the only source is Honda and they sell the complete bearing, but if the inner race is usable you can buy the rollers and/or outer race from a bearing house.

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