English French German Italian Spanish

C3 Bearings

Submitted by leslie,peter_howard on Mon, 14/03/2011
Forums
Heavy Twins

It seems nowadays, everyone specifies C3 bearings for motorcycle engines,I really am baffled by this.

The original bearings used by British Motorcycle manufacturers were nearly always standard clearance items which makes sense. C3 has a looser internal clearance and is usually specified for hot running devices such as electric motors where the spindle is heated by the armature and consequently the inner bearing race is heated more than the outer race and can cause tightening.

In a motorcycle engine it is more likely that the cases are heated slightly more than the crankshafts or at least they are heated evenly by the hot oil splashing about, probably never more than 70-80 degrees C. If a bearing is heated evenly the clearances inside will track the expansion evenly.

Somehow it just seems fashionable to use C3 bearings as if they were a superior bearingbut this is not the case.

This extra clearance or slopping about seems pointless to me especially when the timing side bearing has to drive the oil pump worm and also requires precision alignment to give a good long life to the oil seal at the end.

The "Superblend" bearing rollers have the ability to absorb flexing of the crank so why does it also need toflap about? The extra clearance WILL NOT close up when the engine warms asI have already explained soin effect you are installing a loose bearing that will just wear out the oil seals that much quicker and might run noisier.

Can someone explain why this C3vogue has taken over please?

Les

Submitted by leslie,peter_howard on Mon, 14/03/2011

Permalink

please also read the "C3 Explained"

.uk/shop/p5164/SKF+6306C3+Open+Deep+Groove+Ball+Bearing+30x72x19mm/product_info.html

It Says:C3 Bearings ~ A Brief Explanation

  • The bore, diameter and width of C3 bearings are identical to the non C3 version.
  • C3 are exactly the same quality but have a different a purpose.-------------------------------
  • C3 bearings have additional internal radial clearances to allow expansion in high speed / temperature environments.
  • Typically suited to hot and high speed environments ( fans, high speed motors etc)
  • They can feel loose until at running temperature and speed.
  • They are unsuitable where critical alignment is required from the onset.
  • Unless the bearing you are replacing specifically says C3 on it then you should not replace it with a C3 bearing.
  • A rule of thumb is to replace like for like, there is no advantage to a C3 bearing in place of a standard bearing.

    •  


    Norton Owners Club Website by 2Toucans