On Tue, 15 Mar 2005 19:35:49 -0500, Avi Silterra
may have said:Greetings
Hopefully this is the correct venue to post a question. I was recently
about to purchase a used bike. Myself and the seller had just refilled the
tires with air, as they were soft. Partway through screwing the tire cap
back on the nozzle, lots of air suddenly started escaping, seemingly from
the nozzle. I removed the cap rapidly, air continued to leak until the
tire was very soft. When we
tried to fill the tire again, this time air leaked in large
quantities immediately.
I decided not to purchase the bike until I knew more.
Any idea what might be wrong and how much it might cost to fix ?
Most likely problem: A bad tube. Cost? If all that's needed is a
relacement tube, probably about five bucks plus the time to swap it
out.
Was there a small locknut at the tip of the valve stem which you had
to loosen before you could fill the tire with air? If so, that
locknut needs to be retightened before the cap goes back on; that type
of assembly is called a "Presta" valve. If there was no locknut, and
the connection to fill the tire looked like the same type that's used
on automobiles, you have a Schrader valve. With either type, a valve
that's been sitting for a long period (we're talking in terms of a
usually a year or more, here) may have stuck together internally, and
the sealing material may have torn when the valve was opened to allow
air into the tube. With a Schrader valve, the damaged part can be
replaced separately, but it's seldom worthwhile since the tube is
likely to be in questionable condition if it's old enough for that to
have taken place. With a Presta valve, replacing the tube is really
the only option.
Quoted message said:It didn't seem like putting the tire cap back on could cause that, so
maybe we filled the tire too much and it took a minute to start leaking?
A bike that's been sitting for a while may have dry-rot in the tube.
I see this sort of failure often. The air *seems* to be coming from
the stem, but it's actually blowing out along it. There's also the
possibility that the Schrader valve's body has become delaminated from
the rubber covering on it, but I'm betting that there's a crack in the
rubber right at the base of the valve stem.
One additional caveat; if the tubes are old enough to have
deteriorated, there's a possibility that the tires may be close to
being over the hill as well. If they're blackwalls, you're probably
safe as long as there aren't any visible cracks when the tire is
inflated. If the sidewalls are tan or brown, check to see if the
material in that area is soft and gummy or firm and resilient; it
should not allow your fingernail to leave a dent in it.
Quoted message said:I don't have much experience with bikes so don't know what else might be
the cause or how to fix.
Changing out and/or patching a tube is the one of the most common
repairs required on bikes, and it's pretty close to essential for a
rider to know how it's done. I'd recommend a trip to the public
library for a quick perusal of a bike repair book, followed by a
return trip to the seller of that bike to finalize your purchase. One
other thing that I'd recommend checking out before buying the bike is
the possibility that the tube may have failed due to being punctured
by bubbly corrosion on the inside of the rim, which can only be found
by dismounting the tire. If this bike has been ridden in winter
months, road salt may have attacked the rims.
--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.
