Australian Politics Forum - Replacing bearings on ..... anything

Sprintcyclist

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Replacing bearings on ..... anything
May 12^th, 2021 at 8:07pm

I replaced a few bearings on various machines lately and have learnt and been taught a lot.
Also removed a very badly seized part on a $10K machine with no damage to it at all.
Did some more research lately and am at the stage now where it is no longer just 'theory'.

I used to change bearings by pulling them off with a bearing puller, then tapping new ones on using a perfectly sized socket.
Now, when removing the old bearing off a shaft I clean and lube the shaft. Then use a heat gun to heat the bearing on the shaft.
Then it comes off much more easily.
To put the new bearing on the shaft, I put the shaft in a freezer for a few hours.
Heat the bearing up to about 100 degrees using a digital thermometer for about 10 minutes.
The new bearing slips in fully using hand pressure.

Normal bearings can take 350 degrees, so 100 is easy.
Bearings are very suspect to lateral force. Such as tapping them on with a socket or drift.

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Sprintcyclist Gold Member Offline OzPolitic Posts: 41829 Gender:	Re: Replacing bearings on ..... anything Reply #1 - May 12^th, 2021 at 8:12pm Would never have imagined that heating the 'outside' part to 100 degrees and cooling the 'inner' part to -20 degrees would give such a difference. How much expansion/contraction is there in stainless steel for 120 degrees? How much do you need, to make a difference?
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Bobby.

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Re: Replacing bearings on ..... anything
Reply #2 - May 12^th, 2021 at 8:24pm

Sprintcyclist wrote on May 12^th, 2021 at 8:12pm:

Would never have imagined that heating the 'outside' part to 100 degrees and cooling the 'inner' part to -20 degrees would give such a difference.

How much expansion/contraction is there in stainless steel for 120 degrees?

How much do you need, to make a difference?

Google - the coefficient of thermal expansion.

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Bias_2012 Gold Member Offline Australian Politics Posts: 10766 Gender:	Re: Replacing bearings on ..... anything Reply #3 - May 12^th, 2021 at 9:09pm Sprintcyclist wrote on May 12^th, 2021 at 8:12pm: How much expansion/contraction is there in stainless steel for 120 degrees? The higher the temp, the more stainless steel expands than carbon steel does, if that makes sense https://www.engineeringtoolbox.com/thermal-expansion-pipes-d_931.html
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Dnarever

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Re: Replacing bearings on ..... anything
Reply #4 - May 12^th, 2021 at 9:12pm

Sprintcyclist wrote on May 12^th, 2021 at 8:12pm:

Would never have imagined that heating the 'outside' part to 100 degrees and cooling the 'inner' part to -20 degrees would give such a difference.

How much expansion/contraction is there in stainless steel for 120 degrees?

How much do you need, to make a difference?

Thanks - Always used the tapping method.

Don't have the facility to put my car in a freezer that gets to -20 though that is a bit tough.

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Sprintcyclist

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Re: Replacing bearings on ..... anything
Reply #5 - May 15^th, 2021 at 8:46pm

Bias_2012 wrote on May 12^th, 2021 at 9:09pm:

Sprintcyclist wrote on May 12^th, 2021 at 8:12pm:

How much expansion/contraction is there in stainless steel for 120 degrees?

The higher the temp, the more stainless steel expands than carbon steel does, if that makes sense

https://www.engineeringtoolbox.com/thermal-expansion-pipes-d_931.html

i guess different metals respond to temp differently ?

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Sprintcyclist

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Re: Replacing bearings on ..... anything
Reply #6 - May 15^th, 2021 at 8:47pm

Dnarever wrote on May 12^th, 2021 at 9:12pm:

Sprintcyclist wrote on May 12^th, 2021 at 8:12pm:

Would never have imagined that heating the 'outside' part to 100 degrees and cooling the 'inner' part to -20 degrees would give such a difference.

How much expansion/contraction is there in stainless steel for 120 degrees?

How much do you need, to make a difference?

Thanks - Always used the tapping method.

Don't have the facility to put my car in a freezer that gets to -20 though that is a bit tough.

If you can tape some ice around the shaft for 10 minutes, it might just make that difference.
And warm the bearing.

If you do both, heat the bearing, cool the shaft it'll help.
Grease the shaft

Course you'll probably have to tap it in also.
But, it'll need less 'tapping'

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Sprintcyclist

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Re: Replacing bearings on ..... anything
Reply #7 - May 16^th, 2021 at 7:23pm

yep, this is what I found

Quote:

......... Wow.....I cleaned up the shaft and put the bearing & pulley in the oven for about 20 mins. I then used Cold Spray to cool the shaft.

It all went together so easy! Bearing slid all the way down and pulley went right on too just like butter.

Heat is the key! ......................

https://www.garagejournal.com/forum/showthread.php?t=46113

Wonder what temp he had the oven set too.

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Sprintcyclist

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Re: Replacing bearings on ..... anything
Reply #8 - May 16^th, 2021 at 7:36pm

Quote:

..........Kettle full of boiling water can make huge difference to stuck bearings. Easy too..............

....................+1 for ice and boiling water. Either way around but the bearing needs to be cold and the frame hot. Oven not a good idea as these alloys are heat hardened and I’m not sure what oven temps would do to the material’s performance. ..............

............ Thanks to all those who replied.

Kettle of boiling water worked a treat. ............

https://singletrackworld.com/forum/topic/bearing-removal-using-heat-an-oven/

AH, hot water. great idea. Readily available, great thermal conductivity and thermal mass. Will limit the temp rise to 100 degrees.
Never thought of that.

Ice on the shaft, hot water on the bearing? If you get ANY movement, it will slide off.

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Johnnie Gold Member Offline Australian Politics Posts: 12485 Gender:	Re: Replacing bearings on ..... anything Reply #9 - May 16^th, 2021 at 9:27pm What about sealed bearings?
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Sprintcyclist

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Re: Replacing bearings on ..... anything
Reply #10 - May 16^th, 2021 at 10:01pm

Johnnie wrote on May 16^th, 2021 at 9:27pm:

What about sealed bearings?

good question ..........

Quote:

........ Bearing rings and balls
SKF self-aligning ball bearings are heat stabilized up to 120 °C (250 °F).

Cages
Steel or brass cages can be used at the same operating temperatures as the bearing rings and balls. For temperature limits of polymer cages, refer to Polymer cages.

Seals
The permissible operating temperature for NBR seals is –40 to +100 °C (–40 to +210 °F). Temperatures up to 120 °C (250 °F) can be tolerated for brief periods. ...........

https://www.skf.com/au/products/rolling-bearings/ball-bearings/self-aligning-bal...

Funny, I checked the temp limits of the bearings I put on at work.
It was 350 degrees C !! And they had seals on either side.
I thought up to 100 degrees would be easy for them. I used a heat gun and a digital thermometer to not exceed 100 degrees.
So the bearing temp would have been less.

I guess, check with every bearing ?

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Johnnie

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Re: Replacing bearings on ..... anything
Reply #11 - May 16^th, 2021 at 10:18pm

Sprintcyclist wrote on May 16^th, 2021 at 10:01pm:

Johnnie wrote on May 16^th, 2021 at 9:27pm:

What about sealed bearings?

good question ..........

Quote:

........ Bearing rings and balls
SKF self-aligning ball bearings are heat stabilized up to 120 °C (250 °F).

Cages
Steel or brass cages can be used at the same operating temperatures as the bearing rings and balls. For temperature limits of polymer cages, refer to Polymer cages.

Seals
The permissible operating temperature for NBR seals is –40 to +100 °C (–40 to +210 °F). Temperatures up to 120 °C (250 °F) can be tolerated for brief periods. ...........

https://www.skf.com/au/products/rolling-bearings/ball-bearings/self-aligning-bal...

Funny, I checked the temp limits of the bearings I put on at work.
It was 350 degrees C !! And they had seals on either side.
I thought up to 100 degrees would be easy for them. I used a heat gun and a digital thermometer to not exceed 100 degrees.
So the bearing temp would have been less.

I guess, check with every bearing ?

Most bearings are of the sealed type so be careful where you apply the blow torch because you will melt the rubber seal and the ball bearings within the bearing will not operate properly and could seize.

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Sprintcyclist

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Re: Replacing bearings on ..... anything
Reply #12 - May 16^th, 2021 at 10:20pm

Johnnie wrote on May 16^th, 2021 at 9:27pm:

What about sealed bearings?

Ah, found some good data

Quote:

...... Heat mounting: The temperature difference between a bearing and seating during a heat mounting process will depend on the magnitude of the interference fit and the bearing size.
Normally, a bearing temperature of 83 C above that of the shaft is sufficient.
Unless otherwise specified, open bearings should never be heated to a temperature greater than 125 C.
Extreme heat can cause the bearing’s metallurgy to change, which can alter bearing dimensions and/or hardness.
Sealed/shielded bearings will have lower prescribed heating limits, because of the lower limits associated with the lubricant in the bearings, as well as the seal material. ..........

https://www.piprocessinstrumentation.com/bearings-seals/article/15561605/how-to-...

hhhmmm, so an 80 degree differential.
For sealed bearing, less ........
I am thinking for many jobs, hot water on the bearing, ice on the shaft.
Put the ice on for 10 minutes first.

If it is a small job, a freezer works well. Gives you a -20 degree headstart.

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Sprintcyclist Gold Member Offline OzPolitic Posts: 41829 Gender:	Re: Replacing bearings on ..... anything Reply #13 - May 16^th, 2021 at 10:24pm Mr Walker - yes, a blow torch would not be so good. I had a hot air gun. Hair dryer would be quite ok. AND a digital thermometer or 'calibrated hand'. '......... oohhh, that's pretty hot ......... ' Go to play the heat on it evenly for quite a while to get it ALL to heat up
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Johnnie

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Re: Replacing bearings on ..... anything
Reply #14 - May 16^th, 2021 at 10:53pm

Sprintcyclist wrote on May 16^th, 2021 at 10:24pm:

Mr Walker - yes, a blow torch would not be so good.

I had a hot air gun. Hair dryer would be quite ok.
AND a digital thermometer or 'calibrated hand'.
'......... oohhh, that's pretty hot ......... '
Go to play the heat on it evenly for quite a while to get it ALL to heat up

Good work but not all can appreciate how this works so easily and without knowing what can go wrong, bearings can be tricky.

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