Frequently Asked Questions
Q: What does C3 clearance mean?
A: In the case of crank bearing internal clearances, these are generally C3 or C4, which signifies larger than standard clearance. These are ranges dependant on bearing size and are there to allow the bearing races / balls to expand when used in high load or temperatures.
An example is: (1 micron = 1 thousand of a millimeter)
6205 series
Standard clearance = 5 to 20 microns
C3 clearance = 13 to 28 microns
C4 clearance = 23 to 41 microns
There are also certain bearings where we manufacture specially tightened
clearances to reduce noise levels.
An example would be
6205CS20 = 20 micron clearance +- certain tolerance
For crank bearings we would not recommend plastic caged bearings, the only type we did (and still do) supply in this style, was for the 70's TZ Yamaha, but these are special reinforced, petrol resistant material and were designed to be replaced often.
Q: How do I know if a bearing needs replacing?
A: if you wish to check a bearing for wear, clean in appropriate
non abrasive safe liquid, allow to dry, oil lightly and slowly rotate
using slight force to either side. Any tendency for the bearing to
rotate poorly is a sign that it needs replacement. As always, if in
doubt replace.