Bearing clearance CN C2 C3 C4 ?

[stratcat]

Original topic by unclemeat:

Hello All

Does anybody know what clearance rating we should be using in our ball and roller bearings ?
Wheel bearings i guess must be CN (Clearance Normal) but what about G/box bearings and especially driveside bearings ?

Interference fits on shafts and in aluminium casings, together with temperature fluctuations all play a part in correct bearing selection and clearance rating but does anyone have any proper info for what should be used ?

RHP & SKF bearing manufacturers state the following :

Suffix...

C2  RADIAL INTERNAL CLEARANCE LESS THAN NORMAL-MARKED '0' OR 'C2'

CN NORMAL GRADE RADIAL INTERNAL CLEARANCE-NOT MARKED

C3 RADIAL CLEARANCE GREATER THAN NORMAL-MARKED '000' OR 'C3'

C4 GREATER THAN C3-MARKED '0000' OR 'C4'

Between one C rating and the next is approx 0.020mm

This (by the way) is not the clearance between outer race of bearing and the bearing housing, OR, the clearance between the inner race and the shaft....It is the radial clearance between ball/roller and the outer race.

Also, what are peoples thoughts on using shielded or even sealed bearings instead of the normally open type (especially in G/box).

Firstly,  I am not a qualified engineer so will leave others to answer with superior knowlege about bearing clearance, however I am very much of the opinion that today's engineering tolerances could only be dreamed of in the 50's and 60's and that its not worth getting too worried about such things.
I would assume normal clearance bearings would be fine. The difference of 0.020mm is less than 0.001 inch (unless my maths has gone wrong) much closer tolerances than I reckon manufacturers were working to 50 years ago.

Regarding shielded bearings, I always use them in wheels as they stop all the crud from getting into the bearing. In a gearbox though I would have thought the copious amounts of oil would be a benefit.
Although thinking about it, if you left the outer seal in place (on a shielded type) it would provide a second line of defence from the dreaded gearbox oil seal leak (guess where my A10 leaks from!)

only my 2p worth I'm sure someone more knowledgeable than I will be along to put you right!

[Brian]

On the subject of leaving the seal in the gearbox bearing I have been doing this for years. I remove the seal on the inner side but leave the outer one in. I put some grease between the bearing and the actual gearbox seal during assembly. I have done this to quite a few now and so far havent had one leak or cause any problem.

Quite often when the gearbox seal leaks it is not the seal running on the sprocket but where the face of the seal goes up against the housing. I always use some sealer on the face of the seal when I put them together.

Brian.

[stratcat]

That's good to you have been doing that.
I will definitely do it when I come to rebuild my gbox.

[orabanda]

It is critical if you wish to prevent premature bearing failure, to replace bearings with those of the same specified internal clearance.

This is because the designer has taken into consideration the installation clearances required for the bearing. For example, if a ball bearing was to experience  a medium to heavy interference fit (say .003" - .004"), then a bearing with larger internal clearance will be required.

My personal preference with bearings is to use only the highest quality, as the life of the bearing(s) will determine the life of the machine. I prefer SKF or FAG, and use these in my bikes.

My experiences are based on a working career in an engineering field.

ps, keeping the oil clean is the other determining factor, but thats another story!

Richard

[Brian]

On the advice of the engineers at work I have been using SKF "explorer" series bearings for a couple of years now and have not had any problems.

You might think that bearings are just bearings but I have had new bearings fail so its worth using well know reputable brands.

Brian.

[unclemeat]

SKF and also RHP are all good manufacturers and i like the idea of using the seal on the outer face of the g/box bearing.
Orabanda, do you know the actual clearance rating of say driveside crank bearing ?
Brian, Out of interest, where are you using the explorer bearings, wheels and both g/box bearings ?

[Brian]

I've used the "explorer" bearings in everything for the last couple of years. Wheels, gearbox and engine. I have to admit to not actually knowing how they differ from standard bearings, I'm not sure if they have a difference tolerance or not.

I guess its hard to tell if one bearing is better than another unless it fails but I have noticed a couple of differences. The better ones have more balls or rollers in them than the cheaper ones. Whether they are made of a better quality metal or not I dont know, maybe someone else does ?

[unclemeat]

I think the explorer range are basically super precise bearings that cost a little more than your std bearing..

[unclemeat]

BTW...nice collection you have there orabanda !!

[orabanda]

Thanks mate,
With lots of SKF bearings fitted!
Richard