Oil, rim valve hole, rubber disintegration

[Andrew Lee]

Tire: ~12 year old Specialized Ground Control

Oil source: leaky shock fork. Oil has been dripping out from under the
shock boot and down the left fork leg for the past several years (~4 to 5
years?). Oil reached the hub and flowed along the spokes to the rims. Most
of the oil flow probably happened over a short period of time and the flow
probably decreased or stopped after enough oil was lost. Before I cleaned
up the fork and wheel this past week, a thick layer of dirt and oil covered
the fork leg and front hub, with a lesser layer on the hub-facing side of
the rim. (Yes, I haven't cleaned this bike in years, but I just overhauled
the hubs yesterday...)The rim sidewalls were relatively clean being swept by
the brake pads. The plastic rim strip covered the spoke holes well, but the
valve hole was open to the oil covered hub-facing side of the rim.

The first two photos are from one side of the tire, the next two are from
the other side. The black patch is where the damage is. The yellow gum
rubber (?) is absent from those patches, and when back lit, you can see
light between the nylon threads of the casing. (Sorry, no back lit photos,
my camera's LCD is broken and I can't adjust the settings very well.) The
oil probably got to this part of the tire by flowing down the presta valve
of the tube to the interior of the tire. The rest of the tire is pretty
dirty and has evidence of oil on the outer "skinwall" part, but it is more
of a diffuse damage.

http://img200.imageshack.us/img200/7500/img25659fq.jpg

http://img200.imageshack.us/img200/5199/img25660ky.jpg

http://img200.imageshack.us/img200/5817/img25685hx.jpg

http://img200.imageshack.us/img200/9366/img25698mt.jpg

How did I happen to notice this damage? Well, the tube just suddenly went
flat on me yesterday and when I inspected the tube, I found the leak at the
valve base. Then I remembered the Carl/Jobst/Mark discussion on this topic
a few weeks ago. The tube is a Performance branded tube with one patch on
it. It has been on the bike for years - I don't remember my last flat on
this bike, and I haven't lived near a Performance shop in over 6 years. It
is possible that this is a defective tube, but it has already survived many
years. I haven't had to use a frame pump on this bike in many years, so it
wasn't bad pumping technique (I've never damaged a tube using a frame pump
anyway). I really can't say if the tube was defective or if oil weakened
the tube. Maybe it was a combination of those factors. Here is the tube:

http://img200.imageshack.us/img200/3103/img25705yb.jpg

 

[[email protected]]

On Tue, 19 Jul 2005 21:15:59 -0800, "Andrew Lee"
<whatsupandrewathotmaildotcom> wrote:

>Tire: ~12 year old Specialized Ground Control
>
>Oil source: leaky shock fork. Oil has been dripping out from under the
>shock boot and down the left fork leg for the past several years (~4 to 5
>years?). Oil reached the hub and flowed along the spokes to the rims. Most
>of the oil flow probably happened over a short period of time and the flow
>probably decreased or stopped after enough oil was lost. Before I cleaned
>up the fork and wheel this past week, a thick layer of dirt and oil covered
>the fork leg and front hub, with a lesser layer on the hub-facing side of
>the rim. (Yes, I haven't cleaned this bike in years, but I just overhauled
>the hubs yesterday...)The rim sidewalls were relatively clean being swept by
>the brake pads. The plastic rim strip covered the spoke holes well, but the
>valve hole was open to the oil covered hub-facing side of the rim.
>
>The first two photos are from one side of the tire, the next two are from
>the other side. The black patch is where the damage is. The yellow gum
>rubber (?) is absent from those patches, and when back lit, you can see
>light between the nylon threads of the casing. (Sorry, no back lit photos,
>my camera's LCD is broken and I can't adjust the settings very well.) The
>oil probably got to this part of the tire by flowing down the presta valve
>of the tube to the interior of the tire. The rest of the tire is pretty
>dirty and has evidence of oil on the outer "skinwall" part, but it is more
>of a diffuse damage.
>
>http://img200.imageshack.us/img200/7500/img25659fq.jpg
>
>http://img200.imageshack.us/img200/5199/img25660ky.jpg
>
>http://img200.imageshack.us/img200/5817/img25685hx.jpg
>
>http://img200.imageshack.us/img200/9366/img25698mt.jpg
>
>How did I happen to notice this damage? Well, the tube just suddenly went
>flat on me yesterday and when I inspected the tube, I found the leak at the
>valve base. Then I remembered the Carl/Jobst/Mark discussion on this topic
>a few weeks ago. The tube is a Performance branded tube with one patch on
>it. It has been on the bike for years - I don't remember my last flat on
>this bike, and I haven't lived near a Performance shop in over 6 years. It
>is possible that this is a defective tube, but it has already survived many
>years. I haven't had to use a frame pump on this bike in many years, so it
>wasn't bad pumping technique (I've never damaged a tube using a frame pump
>anyway). I really can't say if the tube was defective or if oil weakened
>the tube. Maybe it was a combination of those factors. Here is the tube:
>
>http://img200.imageshack.us/img200/3103/img25705yb.jpg
>

Dear Andrew,

If oil had gotten onto the inner tube, I'd expect it to feel
softer and to look shiny and darker than the surrounding dry
rubber--the rubber soaks up oil and loses tensile strength.

Cut two chunks of inner tube, dunk one in oil for a few
days, and you'll see what I mean--the oil-soaked tube feels
and looks quite different.

I don't see any traces of oil on your tube, nor any sign of
oil on the valve stem itself--in fact, there's rust where it
meets the tube:

http://img200.imageshack.us/img200/3103/img25705yb.jpg

If the leak is right at the base, I'd wonder a little about
the effect of the rust on a >6-year-old tube.

The damage to the tire sidewall is another matter, but again
there doesn't seem to be any corresponding oily patch of
inner tube.

I'd be pleased to see signs of oil damaging an inner tube
(well, sorry for you, but pleased in a ghoulish way), but to
me your tube looks dry and untouched by oil.

The light shining through the oily patch on the tire is
interesting, probably something along the lines of the Homer
Simpson diet test as prescribed by Dr. Nick:

"And remember, if you're not sure about something, rub it
against a piece of paper. If the paper turns clear, it's
your window to weight gain."

http://www.httpcity.com/ronq/simp/comedy.html

It looks as if the oil dripped directly from shock to
sidewall and spread out, rather than hitting the rim, oozing
through the valve hole, and spreading onto the tire.

Again, there's no apparent oil path from the rim to the
nicely rounded dark smear on the inside of the tire sideway.

Because it's unlikely that the valve-hole area just happened
to be right under the leaky shock all the time, I wonder if
the pictures actually show a non-oil related problem. The
dark smears on the inside might be where the thickened
rubber bulge of valve-area acted like a motorcycle-rim
security-bolt. That is, the smears may show where the
stiffened rubber patch around the valve-stem was causing a
little trouble.

Carl Fogel

 

[Andrew Lee]

[email protected] wrote:
> If oil had gotten onto the inner tube, I'd expect it to feel
> softer and to look shiny and darker than the surrounding dry
> rubber--the rubber soaks up oil and loses tensile strength.
>
> Cut two chunks of inner tube, dunk one in oil for a few
> days, and you'll see what I mean--the oil-soaked tube feels
> and looks quite different.

Good point. I wasn't thinking about how an oiled tube would be different.
There is an irregular shaped bump in the rubber surrounding the valve that
got me thinking that something might have happened to the rubber, but
looking at another (good) tube now, I see something similar. But the good
tube has much better support around the base of the valve. I think this
might be one of those defective tubes that Jobst talked about. It has just
been handled gingerly enough that it lasted so long.

> I'd be pleased to see signs of oil damaging an inner tube
> (well, sorry for you, but pleased in a ghoulish way), but to
> me your tube looks dry and untouched by oil.

Yes, darn for you. I wish that I could say that I was able to tear the tube
up into bits with my bare fingers at the valve...

> Because it's unlikely that the valve-hole area just happened
> to be right under the leaky shock all the time, I wonder if
> the pictures actually show a non-oil related problem. The
> dark smears on the inside might be where the thickened
> rubber bulge of valve-area acted like a motorcycle-rim
> security-bolt. That is, the smears may show where the
> stiffened rubber patch around the valve-stem was causing a
> little trouble.

Good call, I think. The patches are shaped like the stiffened rubber patch
of the the tube.

So, maybe this says something about the difficulty of actually getting oil
on a tube and weakening it enough to cause problems? There was quite a bit
of oily residue on this rim, more than I imagine would be left on a rim from
oiling nipple seats.

 

[Mark Hickey]

"Andrew Lee" <whatsupandrewathotmaildotcom> wrote:

>[email protected] wrote:
>> If oil had gotten onto the inner tube, I'd expect it to feel
>> softer and to look shiny and darker than the surrounding dry
>> rubber--the rubber soaks up oil and loses tensile strength.
>>
>> Cut two chunks of inner tube, dunk one in oil for a few
>> days, and you'll see what I mean--the oil-soaked tube feels
>> and looks quite different.

I wonder what kind of physical (visual) evidence a single drop of oil
getting on that section of the tube would leave. Would it be as
obvious as a tube soaked in oil for days?

I really don't know - I suppose there's a test called for there
somewhere... ;-) Unfortunately the only real-world test would
require dripping a drop of oil or two on my own bike's stem, and
seeing if I have to stop to change a flat due to a stem base failure.
:-(

Maybe I'll do that after it cools off - it's no fun changing a tube
when the temperature is in triple digits!

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

>Good point. I wasn't thinking about how an oiled tube would be different.
>There is an irregular shaped bump in the rubber surrounding the valve that
>got me thinking that something might have happened to the rubber, but
>looking at another (good) tube now, I see something similar. But the good
>tube has much better support around the base of the valve. I think this
>might be one of those defective tubes that Jobst talked about. It has just
>been handled gingerly enough that it lasted so long.
>
>> I'd be pleased to see signs of oil damaging an inner tube
>> (well, sorry for you, but pleased in a ghoulish way), but to
>> me your tube looks dry and untouched by oil.
>
>Yes, darn for you. I wish that I could say that I was able to tear the tube
>up into bits with my bare fingers at the valve...
>
>> Because it's unlikely that the valve-hole area just happened
>> to be right under the leaky shock all the time, I wonder if
>> the pictures actually show a non-oil related problem. The
>> dark smears on the inside might be where the thickened
>> rubber bulge of valve-area acted like a motorcycle-rim
>> security-bolt. That is, the smears may show where the
>> stiffened rubber patch around the valve-stem was causing a
>> little trouble.
>
>Good call, I think. The patches are shaped like the stiffened rubber patch
>of the the tube.
>
>So, maybe this says something about the difficulty of actually getting oil
>on a tube and weakening it enough to cause problems? There was quite a bit
>of oily residue on this rim, more than I imagine would be left on a rim from
>oiling nipple seats.
>