Tony Raven said:If you find it unsightly then just wipe the black off with a cloth,
otherwise just leave it - its doing no harm on the outside but will
do a lot of harm on the inside if you wash it in with fresh oil.
If the outside of the chain is kept pretty clean (a tall order, I know),
lube could be simply added without doing very much harm. Some harm will be
done if the chain is used dry because one can't be bothered to clean it
quite frequently enough.
"One of the great controversies of chain maintenance is whether you should
oil a chain or not. The downside of oiling a chain is that the oil may carry
grit into the interior of the chain, and that this grit-mixed-with-oil will
act as grinding compound, causing accelerated wear. Many experts whose
judgement I highly respect hold this opinion, but I do not believe that this
is always the case. I have no doubt that this "grinding-compound" effect can
occur, but the severity of the risk depends upon the sort of dust/soil
prevalent in a given area, and, particularly, the oiling technique used.
......
"Most of the schmutz that contaminates a chain is stuff that is thrown up by
the front tire. This lands on the outer circumference of the chain. For this
reason, you should always oil a chain on the inner circumference, the side
that faces the sprockets. This decreases the tendency of the oil to carry
crud into the interior bearing surfaces of the chain. The best way to apply
the oil is with a drip-type oil can, along the top of the lower run of the
chain. This applies the oil to the cleanest part of the chain.
"I just run the pedals backwards while applying a line of oil down the
rollers. It takes 15 or 20 seconds to oil a chain this way. In the case of
old-fashioned bushing-type chains, I usually run the oil along the left side
only, in hope that the clean oil will be able to flush through the bushings
from left to right. I have used many different oils, my favorite is Phil
Wood Tenacious oil. "
- http://www.sheldonbrown.com/chains.html#lube
~PB