I found some factors that contribute to fork seal leaks.

1. The large diameter of the fork leg makes for a very long
circumference, compared to that of the small diameter rod used in a
telescopic shock absorber.
There is more area for potentila leaks of air or oil.

2. The oil seal's lips rock back and forth as the forks compress and
rebound. The lips act as a one way valve, allowing the fork to pump up
with excess air pressure. This cause the fork to be harsher than
intended during compression and it rebounds too quickly.

3. The surface finish of the fork tube due to intentional
finish at the factory, or damage in use.

4. The roundness of the fork tube.

5. Barometric pressure changes.

Notes from google search:

air bleed screw (A) located on the cap, in. order to drain the
pressure generated inside. the fork's leg. Check the oil seal (B)
condition; replace if ...
http://www.marzocchi.com/admin/downl...ManualeInglese

The pressure generated by the air that can get. into the fork legs
while the motorcycle is being. used and which, due to the special
shape of the. oil seals ...
http://www.marzocchi.com/System/7238...ry%20Works.pdf

This pressure is produced by the air trapped. inside while riding. Due
to the special oil seal. shape, the air cannot go out, thus causing
some. fork ...
marzocchi.com/System/9172/shiver50USD.pdf

http://www.mcnews.com.au/NewBikeCata...TM_200_EXC.htm
KTM also improved chromium quality of the fork coating to prevent
excessive "pumping up" of the fork in use.

lists.off-road.com/pipermail/wr450/2003-May/000287.html

From: "Paul Giusti" <PGiusti at sunsetscavenger.com>
To: <wr450 at moab.off-road.com>
Sent: Thursday, May 01, 2003 12:15 PM
Subject: RE: [WR450] Front fork seals?


> OK, I'm going to jump in on this discussion because I am leaning towards Steve's side.

In my humble, non-mechanic opinion the reason you have to release
pressure from the top of the forks has nothing to do with the up and
down movement of the fork mechanically "pumping up" the pressure
inside the fork.
>
> Because the forks need to be oil tight they are also air tight.

Changes in barometric pressure due to weather and altitude and heat
changes caused by both changing ambient temperature and heat generated
during use of the fork cause the pressure inside the fork to be either
greater or lesser then outside air pressure. If the pressure
differential becomes great enough it will attempt to equalize though
the oil seal causing it to leak. If you throw in a little dust or grit
contaminating the seal and not allowing a tight fit around the leg
then a leaky seal is almost a given.

http://www.off-road.com/dirtbike/rick/dntask0900.html
FORK SEALS
Rick,
I am a new rider and have recently bought a 95 KX 250 as my first
bike. I have a problem with blowing my fork seals all the time. (snip)

The answer is in your fork tubes. They are more than likely tweaked
and have acquired an oval shape. This would let them pump air into the
forks as you ride, resulting in blown seals. You have two choices:
either spend the money for new (or decent used tubes) or install a
bleeder valve on your fork caps and bleed the air out of the forks
regularly. Have a shop check those fork tubes for out-of-round, or
damaged surfaces.

Potage St. Germaine <(E-Mail Removed)> wrote:

> I am a new rider and have recently bought a 95 KX 250 as my first
> bike. I have a problem with blowing my fork seals all the time. (snip)
>
> The answer is in your fork tubes. They are more than likely tweaked
> and have acquired an oval shape. This would let them pump air into the
> forks as you ride, resulting in blown seals.

Bwaaahahahahaha!

And how would a round fork oval itself without a large blunt instrument?
And an oval fork tube would leak like a sieve anyway.

Drop the subject, there's a good obsessive.


--
BMW K1100LT 750SS CB400F CD250 Z650
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

On Mar 26, 10:20?pm, chateau.murray.takethis...@dsl.pipex.com (The
Older Gentleman) wrote:

> And how would a round fork oval itself without a large blunt instrument?

The kinetic energy in a crash would be quite sufficient to bend a
steel stanchion tube. The first motorcycle I ever owned that had
telescopic forks had a bent tube.

"Oval" isn't quite right. Actually, if a round tube is bent even
slightly, the cross sectional area will become "D" shaped.

If you need proof, just take an old rusted out exhaust header pipe and
cut a section out of it. You'll see that the inner radius of the pipe
flattens itself, while the outer radius remains more rounded.

This occurs even when tubing is mandrel bent.

Example of a problem with D-shaped mandrel bent tubing:

The leading edge slat of the Lockheed L-1011 Tristar had to be de-iced
by hot air bled from the engines.

The leading edge slat was part of a camber changing/re-energization
scheme to enhance lift at high angles of attack and low airspeed.

To achieve camber change and open a path for airflow to re-energize
the boundary layer, the leading edge had to swing smoothly down, so
the anti-icing air ducts had to be round to move smoothly.

We had a special tool in the engineering lab to make the mandrel bent
D-shaped anti-icing ducts round again by ramming a lubricated plug
through them.

The trick was to make the ducts round again, without increasing the
diameter too much or making the titanium too thin. One anti-icing duct
had to slide smoothly into another duct so they wouldn't stop the
leading edge from moving.

> And an oval fork tube would leak like a sieve anyway.

If you agree that an oval fork tube would leak, what's the argument
about, besides "how does a fork tube get bent?"

> Drop the subject, there's a good obsessive.

You drop it. You are the one who is obsessing. You're making a
nuisance of yourself with all your assinine objections to everything I
write.

On 27 Mar, 17:17, "Potage St. Germaine" <flying_boo...@yahoo.com>
wrote:
> On Mar 26, 10:20?pm, chateau.murray.takethis...@dsl.pipex.com (The
>
> Older Gentleman) wrote:
> > And how would a round fork oval itself without a large blunt instrument?
>
> The kinetic energy in a crash would be quite sufficient to bend a
> steel stanchion tube.

No ****, Sherlock.

> The first motorcycle I ever owned that had
> telescopic forks had a bent tube.
>
> "Oval" isn't quite right.

No. It isn't right at all. "Bent" would be accurate.

<Snip usual irrelevancy>


> > Drop the subject, there's a good obsessive.
>
> You drop it. You are the one who is obsessing. You're making a
> nuisance of yourself with all your assinine objections to everything I
> write.

Not everything. But, at the moment, most. You simply do not have the
knowledge or experience to back up your increasingly strange
assertions. Stick to what you know, because by posting complete
nonsense you undo all the good work wrought by your stuff which is
accurate.

On Mar 27, 7:22?am, chateau.mur...@btinternet.com,
<chateau.mur...@btinternet.com> wrote:

> Not everything. But, at the moment, most. You simply do not have the
> knowledge or experience to back up your increasingly strange
> assertions.

The technology of my world must seem very bizarre to you, as perceived
from the fantasy you live in.

I don't wish to post my resume online, but I will say that I have had
the widest imagineable experience and various government agencies paid
for my technical education. You probably can't match my experience,
but I'm not here to compare my experience with yours, I just refer to
it as evidence
to support points I'm making.

> Stick to what you know, because by posting complete
> nonsense you undo all the good work wrought by your stuff which is
> accurate.

If I stick to what I know, that covers a wide range.

If you give up your Robert Shapiro impressions and logic games, this
NG can return to helping newbie fix their motocycles.

Krusty

You DO frequently offer good advice. However, in defence of TOG, much or
most of the tremendous experience you often trot out when you just can't
quit while you're ahead falls under the realm of "military intelligence" .
In this case if the OP's fork tubes were bent even slightly, resulting in an
out of round tube of some complex geometric shape (oval, d shaped, whatever)
it should be painfully obvious to the nekkid eye. Further, the bushing
hidden just under the seal that started this whole fracas, would fetch up
solid upon encountering this "non-round area" long before the leak
supposedly caused by it was noticed.
What I want to know is how to clean the seal without removing it. 'cos if
you have to take it out anyway, why not just replace the damned thing. (you
see I am basically in agreement with your ORIGINAL response).


"Potage St. Germaine" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
> On Mar 27, 7:22?am, chateau.mur...@btinternet.com,
> <chateau.mur...@btinternet.com> wrote:
> If I stick to what I know, that covers a wide range.
>

>
>

Hank <(E-Mail Removed)> wrote:

> What I want to know is how to clean the seal without removing it. 'cos if
> you have to take it out anyway, why not just replace the damned thing. (you
> see I am basically in agreement with your ORIGINAL response).


There's a tool you can get to remove seals in situ, though it destroys
them in so doing. And there's a danger of damaging the fork leg where
the seal sits unless you are *very* careful. Obviously you have to
remove the fork leg from the bike.

It's a weapon of last resort - I last used it when I bought a bike with
a leaking seal, and the previous owner had mangled the allen bolt that
holds leg to stanchion.[1]

[1] He'd also stuffed some rag inside the dust cap to stop the oil
dribbling down and giving the game away, the little tinker.



--
BMW K1100LT 750SS CB400F CD250 Z650
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

Potage St. Germaine <(E-Mail Removed)> wrote:

> > Not everything. But, at the moment, most. You simply do not have the
> > knowledge or experience to back up your increasingly strange
> > assertions.
>
> The technology of my world must seem very bizarre to you, as perceived
> from the fantasy you live in.

Like diesel engines? Inaccurate wiring advice? Telling people to strrip
down their fairings unnecessarily? Having the sheer effrontery to argue
that Europe buys diesel cars because it doesn't have earthquakes? Etc
etc etc

>
> I don't wish to post my resume online, but I will say that I have had
> the widest imagineable experience and various government agencies paid
> for my technical education. You probably can't match my experience,
> but I'm not here to compare my experience with yours, I just refer to
> it as evidence
> to support points I'm making.

Sorry, but whatever you learned in government agencies had very little
to do with motorcycles and motorcycling.

>
> > Stick to what you know, because by posting complete
> > nonsense you undo all the good work wrought by your stuff which is
> > accurate.
>
> If I stick to what I know, that covers a wide range.

It does. So does your ignorance and you seem incapable of separating the
two, nor of admitting you have made a mistake. This is very silly.

>
> If you give up your Robert Shapiro impressions and logic games, this
> NG can return to helping newbie fix their motocycles.

That is not the purpose of this NG, whatever you may believe[1]. And a
lot of the advice you have given would not do that.

[1] Read the charter[2]
[2] You do know what that is, right?


--
BMW K1100LT 750SS CB400F CD250 Z650
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....

"Potage St. Germaine" <(E-Mail Removed)> wrote in
news:(E-Mail Removed) oups.com...
>I found some factors that contribute to fork seal leaks.
>
> 1. The large diameter of the fork leg makes for a very long
> circumference, compared to that of the small diameter rod used in a
> telescopic shock absorber.
> There is more area for potentila leaks of air or oil.

True but what should I do about it? I'm not going to install 20 mm
forks on any of my bikes. It's a fact but not really a "contributing
factor", the same could be said about the thin fork oil - replace it
with grease and leakage would be nearly eliminated ;-)
>
> 2. The oil seal's lips rock back and forth as the forks compress and
> rebound. The lips act as a one way valve, allowing the fork to pump up
> with excess air pressure. This cause the fork to be harsher than
> intended during compression and it rebounds too quickly.

This is mostly talked about among the off road crowd. They use forks
with twice the travel compared to street bikes and much softer springs
that make the difference in spring rate more noticeable.
It does not contribute much to fork leakage because the seal will be
pressed against the tubes by the increased pressure.
>
> 3. The surface finish of the fork tube due to intentional
> finish at the factory, or damage in use.

Factory finish might make the difference between a good and a real
high performance fork. I'd say damage in use (including corrosion) is
the No.1 contributor to excessive fork leakage.
The materials and methods used by the factory will of course
have a huge impact on how long it takes to damage tubes and seals.
>
> 4. The roundness of the fork tube.

Yes, OTOH the seals can cope with some out-of-round because the
tubes does not rotate.
But do not forget radial movement between tube and seal. As the
years pass, the bearings (bushings) wear and the tubes can move
around and will not stay in the centre of the seal. Changing seals on
a fork with a lot of bushing play is pretty meaningless. I'd rate this
as the second most important contributor.
>
> 5. Barometric pressure changes.

No. Fork seals cope with much larger pressure variations than this
without a problem (air assisted forks).

Forget all the exotics! If a fork leaks, you have worn fork
legs, worn fork bushings or plain simple worn fork seals.

And yes, one can try digging out dirt on the seals before
changing them, it has saved money and work for many off road
riders.
Fork gaiters are a good thing in dust or dirt.

If the fork tubes are bent, this problem should be diagnosed
and corrected, time to worry about fork leaks later!

--
Ole Holmblad - Göteborgs Prima MCK / MK Pionjär
TDM850 / TT600R FL#44 OTC#489 UKRMSBC#08
SGFPTH#00 Remove hat to answer by mail

On Mar 27, 9:04�am, "Hank" <u...@nbnet.nb.ca> wrote:
>
> * * You DO frequently offer good advice. However, in defence of TOG

Why would anybody want to defend somebody who lives to troll?