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Press fitting a cartridge bearing onto a BB spindle

Posted: 16 Oct 2020, 8:50pm
by UpWrong
I am changing the left bearing on a TA Light Axix BB. I bought a bearing puller which removed the left cartridge bearing without a problem, now I need to press fit the new bearing. I recall seeing Spa advertising a spacer made by TA and I think the idea was to use a crank bolt into the end of the spindle to push the bearing on by means of the spacer. I can't now find anyone selling the spacer. I believe a socket of the right length and diameter might do. Should this press on the inner race rather than the outer race, or on both, but not just on the outer race?

If I can't find a socket of the right length and diameter, any other suggestions for fitting the bearing?

Re: Press fitting a cartridge bearing onto a BB spindle

Posted: 16 Oct 2020, 9:09pm
by Brucey
you should push on the bearing centre only when fitting a cartridge bearing to a BB spindle. So a piece of tube of appropriate diameter is the usual way; bi-hex sockets may not fit especially well because of bi-hex shape and the fact that sockets are rarely perfectly flat on the end.

If you want to make it as easy as possible, stick the spindle in the freezer, warm the bearing itself (not so hot it damages the seals), use oil, and work swiftly.

hth

cheers

Re: Press fitting a cartridge bearing onto a BB spindle

Posted: 16 Oct 2020, 9:23pm
by UpWrong
Thanks for that. Will see what I have that can push on the centre. Cheers.

Re: Press fitting a cartridge bearing onto a BB spindle

Posted: 17 Oct 2020, 6:06am
by tim-b
Hi
If you want to make it as easy as possible, stick the spindle in the freezer, warm the bearing itself (not so hot it damages the seals), use oil, and work swiftly.

The differential between a frozen component and a heated component is obviously the thing here, but I've often wondered how much difference heating a bearing/frame tube (while avoiding damage to seals/paint) actually makes
The circumference of the inner race (in this case) is small and will give tiny (negligible?) changes from, say, 20C to 100C, what are your calcs on this?
Similar question for the "other" component from 20C to -18C (domestic freezer) with correspondingly small dimensions
EDIT: Does the inner race expand equally in length and circumference, or is it biased to an "easier" direction?
Regards
tim-b

Re: Press fitting a cartridge bearing onto a BB spindle

Posted: 17 Oct 2020, 6:51am
by Brucey
it only moves microns but then microns is all you need to make a difference when it comes to fits of this nature. Except in non-isotropic materials, parts expand or shrink uniformly in all directions with temperature.

Often when assembling suitably accurate parts they slide together by hand when hot/cold and you think "oh, I needn't have bothered" but a few seconds later when the temperatures have equalised, the parts cannot be separated without using considerable force.

On 17mm dia , with steel having a CTE of ~12x10^-6, assuming a delta of 90C (shaft -15C in the freezer, bearing +75C from a hairdryer or something)

then

0.017 m x 12 x10^-6 x 90 = 18.36x10^-6 m

18 microns on this diameter is the difference between a sliding fit and a tight press fit. If the tolerances between the parts are good and there is lubricant present, you should be able to drive the bearing on with no temperature difference (after all this is how the old one has to come off); but if you can use differential temperatures to your advantage it always makes it easier. It is one of those "won't do any harm, usually does some good" type things.

cheers

Re: Press fitting a cartridge bearing onto a BB spindle

Posted: 17 Oct 2020, 7:27am
by tim-b
Hi
1/5 of a human hair, but "every little helps", thanks
Regards
tim-b

Re: Press fitting a cartridge bearing onto a BB spindle

Posted: 17 Oct 2020, 11:12am
by rogerzilla
I used a socket and a Brummagem screwdriver when I changed mine.

Re: Press fitting a cartridge bearing onto a BB spindle

Posted: 17 Oct 2020, 7:06pm
by 6.5_lives_left
I work at a site where they have production lines for electrical machines (generators and motors). Some of the parts are interference fits, i.e. they use the heating/cooling trick that Brucey describes. But they use liquid nitrogen to do the cooling :shock: . Liquid nitrogen is a bit difficult to get hold of. I was thinking what could you use if a freezer wasn't cold enough? Dry ice !

Re: Press fitting a cartridge bearing onto a BB spindle

Posted: 17 Oct 2020, 7:14pm
by Jdsk
Dry ice sublimates at -78°C. Domestic freezers run at about -18°C. From a typical workshop temperature of 15°C (or a heated mating part) that's a big extra difference.

And it's a lot safer to handle than liquid nitrogen. But still causes cold injury very easily and depressingly often. And can cause carbon dioxide poisoning.

Is the extra contraction needed?

Jonathan

Re: Press fitting a cartridge bearing onto a BB spindle

Posted: 17 Oct 2020, 10:35pm
by fastpedaller
I've cooled bearings in the domestic freezer to enable car propshaft universal joints to be assembled easily - works a treat (but you need to be quick :D

Re: Press fitting a cartridge bearing onto a BB spindle

Posted: 18 Oct 2020, 10:29pm
by UpWrong
Just to complete my story, I made a spacer/drift by cutting the collar off an old traditional straight seat post (approx 18mm ID, 21mm OD). I put the BB spindle in the freezer and heated the cartridge bearing with a hairdryer. I applied some oil and used a crank bolt to push the bearing on. Unfortunately the ID of my spacer was insufficient to clear the square taper as it pushed the bearing on down the spindle, and it stopped 1mm short of the bearing being fully home. I used a dremel with a rotary bit to increase the ID of the end of the spacer, and then was able to finish off the press fit.

Since my BB spindle is titanium and this has a lower coefficient of thermal expansion than steel, I used the hairdryer again on the BB with the incompletely fitted bearing before driving the bearing fully home. Job done. :D

Re: Press fitting a cartridge bearing onto a BB spindle

Posted: 18 Oct 2020, 11:08pm
by Brucey
Shame your tool didn't quite work as planned, but if you are using differential heating, you should have worked swiftly. So best use a quick blow with a hammer not a slow wind with a crankbolt; chances are that whatever advantage you may have started with would have been largely lost within five or ten seconds of the parts touching one another, leaving just the differential CTE to help you.

Still, it is done now! And probably you will never have to do the exact same thing again...

cheers