View Full Version : Bearings? what is standard size?

Mart366 - n/a
18-Jul-07, 08:33 PM
I stripped the bearing block down at the weekend, after suspecting & having play in the bearings confirmed.

The drive shaft was ok , so i looked around for replacements.

now i know there are shielded and sealed types, that have there merits, and also bearings can be run with one seal removed, in an oil bath.

So i was looking to order some 6206 bearing with the 2 rubber seals.

This time i was going to order some branded bearings , as on inspection it would appear the bearings i have aren't a major brand.

However i found that the bearings i have are JC3 bearings, which from investigation are over sized, and allow a degree of lateral and rotational play, (possibly what caused the premature failure)

I didnt request C3 bearings when i ordered them, so should i have been given these?

if i now replace them with standard bearings, how much smaller will they be? or will i now need to reorder C3 bearings, which again will fail


team black - n/a
18-Jul-07, 08:39 PM
C3 tends to allow for thermal expansion, if you're running at high speed they're pretty much essential- C3 are genrally used on crankshafts

Mart366 - n/a
18-Jul-07, 09:56 PM
C3 tends to allow for thermal expansion, if you're running at high speed they're pretty much essential- C3 are genrally used on crankshafts

what is high speed? 6800 rpm?

or should i look to using C3 but with an oil bath, as opposed to sealed and lubed


team black - n/a
18-Jul-07, 10:00 PM
6800 would be crank speed for 503s and they use C3 so yes.

Mart366 - n/a
18-Jul-07, 10:02 PM
Cheers, will order asap


Anne Scrimshaw - n/a
23-Jul-07, 10:16 AM
The C denotes the clearance in a bearing. The clearance is the gap between the rolling elements and internal bearing surface. A standard bearing is designated as CN (normal clearance) then C3, C4. As the number gets higher the clearance becomes larger. C2 and C1 as negative clearance – in other words preload – these are only generally used for Linear Bearings.

The Clearance is measured in microns, so to be honest you probably won’t notice the difference.

As Ewan says C3 are often recommended for crankshafts for two main reasons, one is because of the high interference fit – which reduces the operating clearance in the bearing, and also because it is a high temperature application and so has to take into account thermal expansion, which can also reduce the internal clearance. This is made particularly interesting in this case by the different thermal expansion of the shaft and the crankcase. Trying to get such an application so it is contact with the mating surfaces and has a good working clearance when it is stone cold as well as red hot isn’t always easy. But don’t worry about that – the engine manufacturer already has.

If the bearing is run with too much preload the life will be reduced. Too much operating clearance isn’t ideal either. However all of that is irrelevant if you only manage a few hours running time and it fails due to dirt and water ingress.


team black - n/a
23-Jul-07, 06:19 PM
So - no truth in the theory that women's brains shrink during pregnancy then....