Civil discussion only about fork seal leaks

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 ...
www.marzocchi.com/admin/download.asp?IDFolder=126&LN=UK&Sito=usa-mtb&Campo=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 ...
www.marzocchi.com/System/7238/Shiver%2045_Factory%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/NewBikeCatalogue/2003/KTM/200_EXC/KTM_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?

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.

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.

 

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.

 

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.

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

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.

 

No shit, Sherlock.

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

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.

 

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.

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).

 

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.

 

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

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

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.

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?

 

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 ;-)

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.

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.

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.

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!

 

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

 

No, the untrained human eye cannot spot dimensional differences of
less than, say, 0.005". The trained machinist can tell you that a part
is off by 0.001", but the machine shop inspector wouldn't be able to
reject the part if it wasn't out of tolerance, and then he'd still
catch a lot of guff from the manufacturing engineer who would say that
the part still fell within geometric tolerance...

That's a perfectly valid point. Why don't you go to the website that
originated the idea of oval fork tubes and post a reply to that guy
who offered the bum advice? If the fork tube is bent by 0.005 inches,
that should stop free movement of the slider.

Well, it's just possible that an apparently leaky fork seal doesn't
need replacing.

If you want to google "computer designed oil seals" @ www.marzocchi.com,
you may find the following statement:

"Computer designed oil seals ensure the highest seal during
compression and minimum friction during rebound."

This should also imply that the oil seals work best under pressure and
hardly work at all with no pressure on them.

Marzocchi also states, "Every month or after every ride, unscrew the
air bleed screw..." This should be done with the forks in full rebound
and the front wheel off the ground. You'd be able to get most of any
oil seepage off the forks
with a rag, and the rest by doing the 35mm film routine which was
previously mentioned.

Continuing with Marzocchi: "...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 problems."

What problems? Excessive air spring effect on compression, too rapid
rebound, and strange, and unexplained oil leaks that mystify
mechanically naive riders, but play into the hands of the mechanic at
the $tealer$hip, whose mi$$ion in life is the $eparate the cu$tomer
from his ca$h.

 

I don't expect you to *do* anything about it, but it might be handy to
know
that the larger inside diameter seals are more prone to leakage than
the small ID seals used on shocks.

This isn't just a subject for the off road consumer to idly discuss.
The factory engineers are aware of the fork seal problems experienced
in the field and are trying to solve the problem and carefully explain
what's going on to the users of their product so they will buy similar
products in the future.

 

Would you please appreciate the difference between "bent forks" and
"oval forks"?

 

This would be the point I made a long, long time earlier.....

Would it not?

 

Why have you snipped his point about air forks?

 

"Description Motorcycle Technical Discussion."

"Technical", as regards this NG means "having to do with the
practical, industrial, or mechanical arts or the applied sciences."

IOW, "technical" refers to the nuts and bolts of motorcycle
maintenance nd repair in this NG.

We don't need to discuss theory any further than necessary to help the
newbie understand how his motorcycle works.

"Technical" can also mean, "concerned with technicalties or minute,
formal points that only a technical expert would be aware of."

Trying to use that *definition* to defend your trolling activities in
this group is pedantic, but telling a newbie about some tiny technical
detail that he wouldn't be likely to know about is helping him.

If you really want to discuss diesels, or you want a flame war, go to
rec.motorcycle and enjoy the company of all the other trolls.

 

OK, so no, you don't.

"CHARTER: rec.motorcycles.tech

This group is to be used for the discussion of issues relating to the
technical aspects of motorcycles. Discussions centering around repair,
maintenance, design, modification, etc. of motorcycles would be
acceptable. Crossposting to other newsgroups should be kept at a
minimum and only as is relevant to the groups involved. Postings of a
blatant commercial nature or binary postings are not welcome.

END CHARTER.

http://www.faqs.org/ftp/usenet/news.announce.newgroups/rec/rec.motorcycl
es.tech

Please note that this does not mean that the ng exists in order to
educate newbies, as you have stated in the past.

Although that is of course, a useful by-product of the charter.

You have got it wrong *again*.

 

How about this?

Rationale for a charter for a moderated newsgroup called
rec.motorcycles.repair.civil-discussion:

Rec.motorcycles.tech evolved from the high volume (400+articles/day)
rec.motorcycles newsgroup dealing with all aspects of motorcycling.
Technical discussions of motorcycle design, maintenance, repair, etc
often got lost in the general discussions on that newsgroup.

The formation of rec.motorcycles.tech was expected to provide a lower
volume venue for motorcycle technical discussions.

Unfortunately, trolls from rec.motorcycles rapidly discovered the
newsgroup, and useful information was lost amidst a barrage of
trolling posts which mainly came from one individual.

Alternatively to starting a new group, how about if you just excercise
some restraint in your unnecessary responses?

 

I usually use a couple sheet metal screws screwed into the seal, and
yes, you really have to worry about scratching the fork. You don't
really have to remove the fork from the bike, but it makes life much
easier.

I much prefer the "fill full of oil and push" drill.

However, I MUCH prefer a pair of "sealsavers" or MX boots, as I haven't
had to replace ANY seals or had any leaks since I've started using
those.

This includes 88,000 miles on my GSX1100G, nearly 50,000 miles on my
SV-650, and whatever mileage on my DL-650.

And I don't give a shit what people think about how it looks. They
aren't the ones in the garage struggling to replace seals and clean up
rock scratches on fork sliders.

-gc

 

You are *so* right. I remember I fitted them to my Yamaha RD350F2
power-valve from new. People grinned at rubber gaiters on a stroker
sports bike, but eight years later the seals were still perfect.

It had been through two cranks, mind ;-)