The first set of numbers indicate the bearing sizes and type. For most moped purposes bearings will be metric single row bearings. The next number is seals. For engine crank bearings, unsealed is important to allow lubrication of the balls in the bearing. Often the seals are plastic or rubber and removable but avoid metal seals. For external bearings such as for Sealed bearing conversion of wheels, having bearing seals is advantageous to keep out dirt and debris. Regarding the internal clearance, this is VERY IMPORTANT for engine bearings. Because they expand when hot, for engine bearings a C3 clearance rating allows expansion of the bearing to roll smoothly and not bind up.
Additionally it is good to check the RPM rating of bearings, and any additional information regarding loading. Some high quality bearings may only be rated to 1000rpm and despite being a good bearing will fail quickly in a motor. Likewise sometimes the bearing cage materials may be plastics which are not heat tolerant or gas tolerant. Always check
Table of Common Bearing Sizes
This is a list of commonly used bearings and their dimensions. Dimensions are in millimeters. See also the Bearing and Seal Chart for a more comprehensive list for specific brands and models.
|ID||Inner Diameter||Outer Diameter||Width||Usage|
|L17 (FAG)||17||40||10||ZA50 magneto side crank bearings|
|E20 (FAG)||20||47||12||ZA50 transmission side crank bearing|
|6002 (ISO)||15||32||9||ZA50 transmission cover crank side|
|16101 (ISO)||12||30||8||ZA50 transmission cover intermediate side - oil injected|
|16100 (ISO)||10||28||8||ZA50 transmission cover intermediate side - non oil injected|
|6005 (ISO)||25||47||12||ZA50 intermediate shaft main|
|6203 (ISO)||17||40||12||ZA50 output shaft main|
|HK 1816 (FAG)||18||24||16||ZA50 output shaft roller|
|HK 1612 (FAG)||16||22||12||ZA50 second speed gear internals|
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