Guys,

I fitted a new bearing into the rear drum a while ago, seems that the hole in which the bearing fits (Brake drum),has been machined severely undersized, is now pinching the bearing. So my question is; When machining something for an interference fit, is there a known tolerance which is acceptable? I know I've got to fish the damned thing out again and put it right. The funny thing is that on the drum that came with the bike had exactly the same problem. If you stick your finger into the inner race and spin, it feel noticeably notchy.

Thoughts?

Steve

The ball bearing manufacturers catalogues should have that information. I bet you can find it on line. When you installed the bearing in the hub were you carefull to only drive it on the outer race? If not, the bearing may have been damaged on assembly.

littlefield wrote:The ball bearing manufacturers catalogues should have that information. I bet you can find it on line. When you installed the bearing in the hub were you carefull to only drive it on the outer race? If not, the bearing may have been damaged on assembly.

Hi Littlefield,

Yeah I was very careful. Having had a bearing collapse on me in the past I'm on the border of paranoid when installing them now.

Thanks, I'll have a look, see what I can find out.

Where did the bearing come from ? Does it have the correct internal clearance ?

Good question, as it was a while ago now. I've got to go to the store @ the w/e for some other bits...So I'll find out then. I'll take the drum with me also.

If you've ended up with an 'O' fit (C2 in the US ?) then any interference fit on the outer is likely to cause it to close up.

You must use a bearing with a C3 designation in this application. A standard bearing doesn't have the clearance for a press fit. Jim

comnoz wrote:You must use a bearing with a C3 designation in this application. A standard bearing doesn't have the clearance for a press fit. Jim

Hi Jim,

Forgive the newbie question, how will I know it's a C3? Will it have C3 stamped on the race somewhere?

Cheers,

Steve

It will be at the end of the part number. Usually, but not always, stamped on the bearing also. Jim

Ah, right ho Thanks!

Hi guys,

More on that bearing.

I just got off the phone to Les at Norvil, seem the bore in the brake hub should have been machined to 39.750...Mine was machined...Or not as the case may be to 38.970 (According to my calipers).

I also learned that I'm supposed to heat the drum before the bearing insertion, something that doesn't seem to be in the manual either.

Any idea as to what temperature it should be?

I seem to be learning something new...every day!

Steve

this link is to nominal tolerances for imperial bearings on the SKF site

http://www.skf.com/skf/productcatalogue ... =1&lang=en

Or if you look at the links in the top right of this page there is a lot of information about bearing fits etc

http://www.skf.com/skf/productcatalogue ... 1010021808

Hmm. I got a replacement (Genuine Norton....um, Made in Slovakia ) that does not note C3. It states FAG 4203BB.TVH. The original English bearing simply states a 4203 without a suffix. Same dimensions. I just hope I don't suffer binding like yours.

Hegel wrote:
I also learned that I'm supposed to heat the drum before the bearing insertion, something that doesn't seem to be in the manual either.

Any idea as to what temperature it should be?

I seem to be learning something new...every day!

Steve

I put the part that I want to expand in the oven at 250 (F) and let it heat for 30 to 40 minutes. I take the part I want to shrink and put it in the freezer for a few hours; I have, yet, to find a Commando bearing fit that isn't a piece of cake using this method.

RS

Anglophile,

Yeah that's the same one as I've got. Interestingly I spoke to an engineer from Schaeffler , he recommended a bore diameter of 39,996 to 39,980 mm.

RS,

Thanks! Mrs H is out tomorrow, so I'll make use of the oven!!

Once heated do they generally still need to be driven home, or are they a bit like popping bearings into an alley case?

Thanks again,

S