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Crank and bearings questions

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Posted by: woody 67---------------------

I had a piston go on my bike 83 CR 250 piece of the skirt broke off . Looks like PO did the bottom end and reinstalled cylinder with broken sleeve witch led to the broken piston skirt .
To my question I split cases throughly cleaned bearings they spin smooth as silk with no play . Should I oil the bearing with something before I reinstall crank ? I know many say to replace bearings, but I cleaned them out real good with carb cleaner and compressed air . I did kill the bike as soon as I heard the rattle , so it didn't run for that long with the broken piston .


Posted by: nickyd---------------------

yeah, i'd oil them. if you split the cases and don't want the expense of the bearings, at a minimum, replace the seals (unless they are under the bearing at which point you'd be pressing out the old bearings and yada yada ya). That's my .02


Posted by: crazy4nitro---------------------

hopefully you didnt "rev" (spin W/ compressed air to dry them)the bearings,if so there done.!.no matter what. trust me.


Posted by: woody 67---------------------

I didn't rev spin them , but I have heard that before and thats why I didn't. Anyone know why rev spinning with compressed air damages bearings?


Posted by: nickyd---------------------

Quote:
Originally Posted by woody 67
I didn't rev spin them , but I have heard that before and thats why I didn't. Anyone know why rev spinning with compressed air damages bearings?


its bad because it makes a really cool sound and we aren't supposed to be able to hear that!! just kidding..I'm curious too, why?


Posted by: woody 67---------------------

Maybe we should ask mythbusters . I think its some highschool teacher that didn't want to hear that sound, but if anyone knows ...


Posted by: Masterphil---------------------

To the best of my knowledge, the bearings ride on a thin film of oil, they don't actually contact the races. If you take that oil away the bearings will spin directly on the races, metal to metal contact is not good. There is a much greater chance of scratching a bearing when it is dry, that's why as soon as you clean them it is a good idea to oil them ASAP.


Posted by: crazy4nitro---------------------

my understanding is that it wears the "cage"(for lack of better words) that holds the bearings in place as well as the surface of the ball itself unevenly. This results in the vibration that compounds wear because of "bare" metal to metal contact.

In other words lots of things are shaking hands that are not suppost to.

Crazy


Posted by: viking20---------------------

Off course bearings should always be oiled , but they wont be ruined , unless its done for several days....!
Never , ever , put an old worn out bearing on a finger and give it a spin with compressed air , if it seizes , OUCH.....



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