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[Dennis C]

That's true Tim, but it won't stop them trying.

[PeteF]

Interesting Dennis and Tim.
Does the weld actually pull the metal of the bearing in slightly?
Does this work on OD surfaces and pull the metal out?

[Dennis C]

Sorry Pete I don't know why it works and I would only use it as a last resort for two reasons, first because I can't answer your question and secondly because I am a crap welder. Does the heat expand the bearing enough to force the housing bigger so allowing a looser fit?, if so then not a thing to do.

[Bullet Whisperer]

Hi Dennis and Pete, the reason it works is the weld is very hot, obviously, and as it cools, it contracts, shrinking the outer race or valve seat as it does so. this reduces the O.D. of the race / valve seat just enough to make them lose their interference fit and fall out. Cheers, Paul.

[papasmurf]

a demonstration:-
https://www.youtube.com/watch?v=zmnXDGlbmgI

[PeteF]

Thanks Paul and Papa, you wouldn't think that would work (well, I wouldn't anyway)
"A day without learning is a day wasted"

[papasmurf]

Pete F is because aluminium has a higher coefficient of linear expansion than steel. The aluminium expands far more than steel does when heat is applied:-

http://dev.physicslab.org/PracticeProbl ... cients.gif

[Bullet Whisperer]

The bearing outer race CONTRACTS when it cools after being welded, that is what makes it loose. The alloy may warm a little and play a small part in the loosening process, but this method also works when an outer race is housed in a steel structure, so it is the shrinkage of the outer race that is the crucial aspect of this method.

[papasmurf]

Bullet Whisperer the steel in steel situation is still has coefficient of linear expansion involved because due to it thinness the race loses heat quicker than steel it is pushed into.

[Bullet Whisperer]

Put it this way, if you could measure the O.D. of the bearing race before and after welding, afterwards, it would be slightly less once the welds have cooled.