Conference noted::bicycle

    I don't ride mountain bikes, so I'm not sure about the pedals, but
    about  the  bottom  brackets  (and  hubs): There are two different
    "sealed"  systems. The first (and better) is what Phil Woods does;
    he  uses industrial cassette bearings which are really sealed (you
    can't  rebuild  them,  adjust them etc.) When a cassette wears out
    (which  I'm  told  takes  10k miles) you replace the cassette. The
    second  (cheaper)  system  is "sealed mechanism" or similar words.
    These  have  a  labyrinth  to  prevent  grit from getting into the
    bearing,  but  internally  they  are  the same as standard hubs or
    bottom  brackets, complete with adjustable cones or cups and loose
    bearings.  Labyrinth  seals help in "normal" use (for a road bike)
    where  there  is  spray and grit, but don't work when you submerge
    the  bearings.  I think that sealed bearings do stay clean even if
    you submerge them, but even they probably can't take that forever.


--David

Sealed cartridge bearings do NOT work for stream crossings.  I've tried it.
The next day the cartridge bearing were sqeeking loudly until I repacked them.

-Jeff Bell

I took the bike in last night for a tuneup, and asked the shop owner
to give the pedals a twirl.  You guessed it, they worked great!

Arg.  I suppose that the grit must have been on the outside, and after
the bike dried out, it fell off.

Whatever...wow, these labyrinth-sealed bearings are great!  :-}

.jim

< Note 393.2 by TALLIS::JBELL "Wot's..Uh the Deal?" >
                             -< not really sealed >-

Sealed cartridge bearings do NOT work for stream crossings.  I've tried it.
The next day the cartridge bearing were sqeeking loudly until I repacked them.

-Jeff Bell

       If you  repacked them they weren't cartridge bearings. Sealed
       cartridge  bearings  can  be replaced, but not repacked. They
       may have been "sealed mechanism" bearings.

--David

> A set of baffles between the bearings and the cruel world outside.
> Is that really the way the labyrinth seal works?  

	Yes.  It forms a labyrinth through which dirt and dust has
	to go to find a path to the inside.

> Is it better or worse than using plain old "O" rings for seals?  

	It is less subject to wear and causes less moving friction but
	is not as effective a a contact seal such as an "O" ring or
	"sealed cassette".  You can get a slightly better seal by 
	filling the labyrinth with oil or grease but then you would 
	have to clean it out and re-lubricate it occasionally like 
	an un-sealed bearing.

> What method is used for sealed cranksets?

	The best are "sealed cassette" where there is a contact (lip)
	seal on both sides of each set of permanently adjusted bearings.  
	The "sealed mechanism" has a normal set of bearings and cones 
	with contact seals where the spindle leaves the bottom bracket 
	shell.  The bearings have to be adjusted properly and may need to
	be lubricated occasionally. The "sealed mechanism" does not
	protect against dirt arriving in the bottom bracket shell via
	the down tube, seat tube or chain stays.

< Note 393.4 by ULTRA::WITTENBERG "Delta Long = -d(sin A/cos Lat)" >
                                              -< you can't repack cartridge bearings >-

>       If you  repacked them they weren't cartridge bearings. Sealed
>       cartridge  bearings  can  be replaced, but not repacked. They
>       may have been "sealed mechanism" bearings.
>--David

OK,.... it depends on what you call repacking.  What I did was to pop the
little rubber grease seals off, rinse it out with solvent, and squirt a bunch
of new grease in.  The old grease was rusty colored, but the new grease fixed
the squeaking problem.

They were the Specialized brand sealed bearing hubs.  I've replaced the
bearings in the past, but this time I didn't have any handy.  If those don't
qualify as sealed cartridge bearings I don't know what does.

-Jeff