Cleaning fork seals instead of replacing them

Hi all--

Have a 1980 Yamaha DT100 with about 1900 miles on it. The fork seals are
leaking. A mechanic told me that often, if you raise the fork seal
(without taking the forks off) and get all of the grit from around the
seal, it almost always fixes the leak. Here's my question -- has anyone
tried this, and how would I get the fork seal off a fork that is still
on the bike? Thanks

-J

 

He was actually the lot boy that sweeps up and moves motorcycles
around. The shop manager promised to teach him to be a motorcycle
mechanic when he's 18...

The fork oil seal is what is called a "lip seal". The seal is V-shaped
in cross section, and the sharp edges of the V are what seals the oil
into the fork leg.

If the edges wear off, the seal leaks because the contact pressure is
reduced due to the increase in area at the points of contact...

Oil seals have a coil spring inside whose ends are hooked to each
other making a circle. It's called a "garter" spring because a garter
was what a woman used to hold up her nylon stockings before the
invention of pantyhose.

The spring has a certain amount of tension on it, but whatever tension
it has is not enough to keep the lips from sealing when they are worn
flat from being abraded by dust and grit.

No, I never even heard of that idea. Maybe the "mechanic" was
successful in wiping off all the oil that wept past the seal because
of air pressure changes while the bike sat in the garage over the
winter.

Summer air is usually higher pressure because of solar heating and air
gets trapped inside the fork. Winter air is colder and lower pressure
because of the dampness. Air trapped inside the fork during the summer
pushes oil past the seal during the winter.

So the mechanic wipes off the weepage around the
oil seal and strikes the forks up and down and sees no ummediate
leakage. He charges the customer for
his "expertise" and sends him on his way. A few weeks or months later,
the customer's forks start leaking badly...

Well, you could remove the fork caps and fill the forks all the way to
the top with motor oil. Then ride the motorcycle over a jump and land
on the front wheel. The fork seals will be blown out by oil pressure.
What a mess.

You might as well plan on removing the fork legs and
disassembling the forks and replacing the seals properly.

 

Er, no, wrong.

You can't. You *can* (however) replace a fork seal without dismantling
the forks.

 

This is nonsense.

 

***********************************

************************************

The only way the seals will come out without dismantling the forks, is
to fill each leg completely with fork oil and, using a tie down or
press or something to help compress and hold the forks compressed,
push the seals out hydraulically with the fork oil (after raising up
the wiper and removing the locking clip/ring from above the seal).

This is messy, and I would only do it off the bike, with the fork
leg in a bucket and a rag wrapped around the seal area. If you go to
that much trouble and don't want to dismantle the forks completely, I
would go on and wash the forks out with automatic transmission fluid,
put in new seals, and fill to the proper level with fork oil.
If I dismantle the forks, I always clean the internals with kerosene,
and rinse them with contact cleaner before reassembly.

On the bike, you can try cleaning the seal by:
1. Raise the fork wiper.

2. Clean the area above the seal (and below the wiper).

3. Using a strip of 35mm film negative (some use a cut * shaped piece
of plastic soda bottle, but whatever you use, it needs to be smooth):
a. Work the plastic down between the seal and fork tube,
b. Rock the rear of the plastic down (moving the front of the plastic
upward),
c. Slide the plastic out back, up, and most of the way out, dragging
any grit out of the seal's sealing surface with the top edge of the
plastic.
d. Wipe the plastic clean after each stroke.

4. Repeat this "sawing" motion with the plastic strip, at least all
the way around the seal. I do this twice around the seal.
If it is very gritty, with much debris, I will clean the strip and
repeat the procedure.
* * *
I only use this procedure IF the fork seal is just barely weeping,
to make sure I need to go through the trouble of completely servicing
the fork.
If the fork is losing enough oil to make a puddle while it is in a
relaxed position (relaxed = bike is not in the truck or trailer with
the forks compressed with tie-downs), I just replace the seal and be
done with it..
A puddle of oil on the floor below a fork leg, at anytime, usually
means a new seal is in order.

For travel, I always vent the forks after compressing the tie-downs,
if possible. Most of my old Yamahas had Schrader valves on the top of
the fork caps, but not sure if the DT100 did.
I added KTM fork bleeders to the fork caps on my GasGas.

Mark gave you excellent advise. He always does.
Those are indeed, some of the easiest forks you will find to work
on.... IF, you read the service/shop manual on them first.


Wudsracer/Jim Cook
Smackover Racing
'06 Gas Gas DE300
'82 Husqvarna XC250
Team LAGNAF

 

Wrong.

There's a tool for it, and I've used it.

 

Summer air is usually higher pressure because of solar heating and air

It is also a very wise idea to change the air in your tires as the winter
air will give you a false tire pressure because of the moisture. Summer
air, having more helium in it, allows for better tire pressure thus your
bike will ride higher on the surface of the road. A friend of mine fills up
old propane bottlesd with summer are to insure he has enough to last all
winter.

 

Wow. I have to save this. I think I'll frame it on my wall.

-gc

 

Thought you'd get a kick outta that!!! ;-)

 

Motorcycle forks will breathe air in and out past the fork seals with
barometric pressure changes. All the fork oil should be in the bottom
of a conventional fork, but the pressure changes will cause the fork
seals to weep oil even though the fork isn't stroking up and down.

There are other pressure and humidity effects that a
sportbike owner should know about.

I used to push my motorcycle out of the cold garage where it had been
sitting all week and check the tire pressure and I would always find
it was about 1 or 2 pounds low, so I would add air.

I thought I might have a slow leak...

When I got to the twisty mountain roads about 15 miles away, my tires
would be up to operating temperature and they would feel a little
skittery because of 2 PSI too much air in the tires...

Dry air expands proportionately to the temperature rise. I figured it
rises about 1 PSI for every 10 degrees F inside a motorcycle tire.

It's not too difficult to deal with rising tire temperatures below the
boiling point of water.

Moisture in compressed air will heat up and expand to 1300 times its
original volume when your tread temperature gets above 212 degrees F
on the race track. That makes adjusting tire pressure a bit more
complicated if you filled your tires from a compressor without first
blowing all the moisture out of the receiver...?

Tire shops claim that filling your car's tires with nitrogen will
somehow make them run cooler and last longer. Actually the nitrogen in
the tanks they use is DRY nitrogen.

But, if you start out with moist air inside your tire, and you inflate
it to the operating pressure with dry nitrogen, how is that supposed
to get residual moisture out of the tire?

I was doing pressure decay tests on stainless steel ducting in a high
temperature oven as part of a qualification tests for Yokohama.

They had bought a license from our company to make the pneumatic
ducting for F-15's in Japan, so I had to run the series of tests.

Pressure decay tests are reasonably simple. You pressure the test
article with compressed air and put the part into the oven and see how
long it take for the pressure to decay down to some level.

Problem was, the air pressure wasn't decreasing as the part heated, it
was increasing wildly. I had to use dry nitrogen to run my tests.

 

This is complete bollocks.

Think air suspension. Think air fork conversions. They manage fine.

Think that even if there was that much pressure change (and there
isn't), if the fork seals allow the air past the seals as you claim,
*the fucking pressure would equalise*.

Think rear shocks. If what you post is true, then rear suspension units
would piss oil as well. They're the same units, effectively.

Christ, you post some crap.

 

I actually can't figure out whether he's taking the piss out of Green
Pea or whether he believes this. If he's gently trolling GP, he's doing
it superbly.

 

Tyre pressures should always be checked cold, for precisely this reason.
Also, I seriously doubt that you could tell the difference between a
tyre at precisely the correct pressure and one 2psi over-inflated.
Possible, but unlikely.

 

Yamaha put tire valves in the fork caps on their first 250cc DT-1
Enduro because they were concerned about air leaking past the fork
seals, causing a buildup of pressure that resulted in excessive air
spring effect.

Riders were advised to "burp" the forks when they
moved to a higher elevation and also when they were riding over rough
terrain.

My GSXR sat in the garage unridden for about two years while I was
recovering from a work injury.

When I finally rolled it out of the garage, there was
fork oil running from the seal down the slider and making a tiny
puddle.

The oil level in the forks couldn't have been as high as the oil
seals.

I was left with two possibilities.

The first is that air pressure changes cause fork seals to weep.

The other possibility is that my tom cat pisses fork oil...

 

You don't think the world has moved on, in terms of construction and
seal technology, since then?

And were it even true, then the difference in pressure would be tiny.
And the fact that this advice is no longer given suggests that it was
about as useful as the old Britbike advice to remove your piston after
the first 500 miles and sand down the high spots with wet&dry paper.

Christ, I cannot believe you can be this stupid. Seals dry out, if left
over time. They harden fractionally. I've had it happen. That's what
happened to yours.

My local dealer said it's a common occurrence with bikes that sit in the
showroom for ages. He now does a tour of the showroom every month or two
and pumps the forks of the bikes just to get some oil on the seals. It's
a good tip, and I do it now, as some of my bikes hibernate for months.

And I see you've conveniently ignored my reference to air suspension.
I've ridden bikes with air-assisted forks across mountain ranges, and I
can assure you you'e talking crap.

Look, for ****'s sake, stop posting your perceived wisdom as truth. If
you really want to help newbies, post something accurate, as you do from
time to time.

 

Sorry OG, I was taking the piss out out of him. When some one comes up with
something so far fetched, it is easy to come back with double. I will
attempt to be a little more 'slack' next time. ;-)

 

More to the point, B-12 has somehow missed the fact that in "RWU" forks,
the air is _between_ the oil and the seals, so it's a bit of a mystery
how changing air pressure could possibly force oil past the seal. Now
then, if the forks got moved when B-12 moved the bike, and if the seals
had dried out in the meantime...oh wait, that explanation doesn't
involve air pressure. It can't be right. ;-)

--
Later,
John



'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.

 

Heh. It's less far-fetched that Green Pea's "Europe buys diesel cars
because they don't have earthquakes" proposition.

Nicely done, sir.

 

Bwaaaahhaahaha!

Yes, I missed that.

Of course, USD forks will leak like sieves. But not in Australia.

 

It has also moved along in damper valving technology. What Japanese
suspension engineers perceived as excess airspring effect from leaky
oil seals was actually caused by the velocity sensitivity of fixed
orifice damper rods in some of their forks.

Why they included "burp" valves in forks that
already had compression blow off valves in them may remain an unsolved
mystery. GOK what engineer made that decision.

Motorcycles emanating from Russia, China, and India are usually just
as crude as you describe.

And what's your theory about how the fork oil rose up out of the
bottom of the sliders? The fork oil just barely covered the top of the
damper rods and that was 4 or 5 inches below the level of the oil
seals.

You don't have "mountain ranges" in England, you have mole hills like
the Cotswolds. OTOH, I can ride from below sea level to over 10,000
feet around here and those two points are within 30 miles of each
other.

And, if you're riding a motorcycle with around 7 PSI over ambient in
the forks, that's almost half an atmosphere over ambient pressure. Not
much air at 14.7 PSI is going to past the seals to get into a fork
pressurized at 21.7 PSIA.

OK, and you should stop being so sarcastic with the
newbies and stop telling them to go RTFM.