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Posted by Masospaghetti on March 24, 2007, 11:50 am
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
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Posted by Mark Olson on March 24, 2007, 11:19 am
Masospaghetti wrote:
> 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
There's two seals on each fork leg, the one you can see, and another
one hidden underneath it. The one you can see is called the dust
seal and its purpose is to wipe the fork leg clean to keep dirt and
crud off the _real_ fork seal which is underneath. Cleaning the dust
seal won't keep the fork seal from leaking. The forks have to come
off to change the seals. Fortunately it is not a difficult job on
a little bike like your DT100.
You should get a service manual and read up on the details before you
start. If the fork tubes are scratched or pitted, the new seals will
soon fail. Damaged fork tubes can sometimes be repaired or rechromed.
--
'01 SV650S '99 EX250-F13 '98 ZG1000-A13
OMF #7
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Posted by Potage St. Germaine on March 24, 2007, 11:53 am
> 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.
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.
> Here's my question -- has anyone
> tried this,
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...
> and how would I get the fork seal off a fork that is still
> on the bike?
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.
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Posted by The Older Gentleman on March 24, 2007, 12:29 pm
> 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.
Er, no, wrong.
>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?
You can't. You *can* (however) replace a fork seal without dismantling
the forks.
--
BMW K1100LT 750SS CB400F CD250 Z650
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....
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Posted by The Older Gentleman on March 24, 2007, 12:29 pm
> 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.
This is nonsense.
--
BMW K1100LT 750SS CB400F CD250 Z650
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....
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