C3 wheel bearings - why, why not?

Ventodue

Hero member
I'd appreciate some advice from some of you real engineers, please  :smiley:

I've always been led to believe that the greater internal clearance of C3 (etc) bearings is so that they can be used in high speed, high heat environments.  Or, to put it another way, "Typically used when the difference between the shaft and bearing housing surface temperatures is between 70?F (40?C) and 130?F (72?C )". Source: Cooper Bearings.

Which heat differential doesn't, I believe -?, happen with a motorcycle wheel  ...

So why are the bearings that are currently sitting in my Zan? Formula rear wheel C3s?  I have no reason to believe they've been changed since leaving the factory; and the parts book does NOT list them as being C3, btw.

And does it matter anyway? (yup, you've guessed; replacement CN bearings are sitting on the bench, waiting to go in).

TIA

Craig
 
N

noneglibob

Guest
Hi Craig,
Firstly let me say I`m not an engineer, but I do buy bearings quite frequently. The C3s have a slightly bigger clearance than 'normal', however, if you read the manufacturing specs there is actually a significant overlap in terms of tolerance between a C3 and a standard bearing.
C3s are more usually specified where the bearing will get very hot, such as in a cylinder head or a gearbox. I'm sure they'd work well enough in a wheel but I doubt if they are the manufacturer's recommended fitment.
Bob
 

laverdakeith

Hero member
My guess is they probably had some lying around. C3's generaly work out a bit more expensive than "normal" deep groove ball bearings and are not necesary for use in wheels.


    Keith.
 

1200ts

Senior member
Location
USA - California
C3 bearings are most commonly used on motorcycles when the bearing is a press fit. Be it either the outer part of the bearing is under compression such as in an aluminum housing or the inner race has expanded when it is pressed on to a shaft or both. As an example, on the 750's cam bearings, where it is pressed on to the camshaft and is under compression due to the shrink fit when the head is cold, standard clearance bearings will be locked up solid. As for wheel bearings, I have seen C3 clearance and standard clearance bearings on a number of different brands of bikes. It all depends on how the bearing is mounted. Heat is not something to be concerned with on a wheel bearing, as even at 100mph the bearing is still turning very slowly. If your bike has 3C from the factory, then stick with them.


From NTN Bearings catalog:
C3 is typically not referred to as a fit; it is the internal clearance in the bearing as defined above. A bearing fit is how tight or loose the shaft and housing hold the bearing in place. When either of the rings of a bearing is tight fitted to its mating component (i.e. the shaft or housing), the resultant deformation of the ring causes a reduction in the amount of clearance in the bearing. A rotating bearing also produces heat due to material stress and through friction from rolling and sliding contact, lubricant shear, and seal contact. The bearing housing is usually stationary and is therefore better able to conduct heat away from the outer ring of the bearing. As a result, the temperature of the inner ring and rolling elements is usually 5 to 10? C higher than that of the outer ring. This results in greater thermal expansion of the inner ring and thus reduces the clearance in the bearing. If the shaft is being heated or if the housing is being cooled, the temperature difference will be even greater. Selection of the proper initial bearing internal clearance must take all the foregoing factors into consideration. Assuming this has been done, it is never advisable to replace a bearing with one having a lower initial clearance. By the same argument, it is usually safe to substitute a larger clearance when the desired clearance is not available
 

Ventodue

Hero member
1200ts said:
C3 bearings are most commonly used on motorcycles when the bearing is a press fit. Be it either the outer part of the bearing is under compression such as in an aluminum housing or the inner race has expanded when it is pressed on to a shaft or both. <snip>

Thanks.  This seems to say that a steel race bearing that is a tight fit in an aluminium housing can be sufficiently reduced in diameter so as to cause the balls themselves to run tight.

Hmmm ... ???

Regards

Craig
 
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