Cleaning fork seals instead of replacing them

Well, 25 years ago, Honda put a schrader valve and a crossover tube on
my CB900's forks, and declared that the system was to be pressurized to
(I think, without checking the specs) around 10 PSI for normal
operation. So I do, and the fork seals hold that pressure nicely for
months and months of riding.[/QUOTE]

Considering that forks are quite similar to hydraulic cylinders used on
farm equipment that handle upwards of 2200 PSI, a few PSI of air pressure
will not cause a good condition seal to leak as your experience confirms.

Grit and age are seal killers.

- Nate >>

 

*Ding*

with accompanying glockenspiel carillon.

 

Apples and oranges. A hydraulic cylinder that produces linear motion
is designed to be completely filled with hydraulic fluid, and air is
NOT tolerated because a smooth push is mandatory.

And, hydraulic cylinders are generally used for slow pushing,
generating a lot of force. If you want something to operate really,
really, really fast, you use a pneumatic cylinder. Fast acting
pneumatic circuit breakers are used to protect high voltage
transmission lines that need to clear faults in 0.004 seconds.

When I worked in the aerospace ground equipment maintenance shop at
Edwards AFB, I did oil changes and engine changes and a lot of general
repairs, even though I was an aircraft electrician. They had too many
electricians, not enough mechanics, so I was sent to help out in the
AGE shop where they had lots and lots of engine driven generator sets
that were built from aircraft parts.

The dedicated hydraulic specialist who talked to me about things like
the difference between a seal leak and weeping seals
also explained what the horrible groaning sound was that came from the
plumbing in the mobile unit that was affectionately called a
"hydraulic mule".

The groaning sound was trapped air bubbles in the system. There was a
large hydraulic reservoir and an electric motor turned a pump that
provided pressure to the hydraulic cylinders.

If you have ever been around an airplane when it is up on jacks and
the ground crew is doing a gear retraction test, you'll hear the
groaning of air in the system, and the hydraulic mechanic
will be doing everything he can to purge air out of the hydraulic
system as he flushes it.

He will never get all the air out of the system, and he will never
stop all the weeps and leaks. If you walk around under an airplane
you're going be dripped on by hydraulic fluid.

No matter. The ground crew has cases and cases of hydraulic fluid.

However, the landing gear struts themselves are very analagous to a
motorcycle fork.

The pneumatic oleo strut is designed to be extended by air pressure
and the oil in the strut is for damping motion. I have personally
taken oleo struts apart and marvelled at the complicated valving
inside.

The pneumatic oleo strut only has to hold air for a matter of days at
the most, it doesn't matter that much if it all leaks out while the
aircraft is parked, but the pilot will have a rough landing if it all
leaks out in flight.

I was driving a jeep past a B-57 bomber parked on the apron at
Edwards, and I noticed that the nose was almost on the ground.

B-57's were already very low to the ground, they were originally a
British design called the "Canberra" and Brit designers wanted the
engines buried in the wings instead of in nacelles hanging underneath.
With engines in the wings, the landing gear can be much shorter.

The mechanic I was with said that the strut had just collapsed from
all the air leaking out of it and that it was no problem to recharge
the strut with a mobile air compressor, which he would check out from
the aerospace ground power yard I was working at.

But that doesn't explain why brand new fork seals weep...

 

Try getting the weight off the front of the bike, then wiping the stanchions
with some isopropyl to degrease them. Next, put a layer of masking tape,
and only one layer, on the stanchion just above the dust cap. Bounce the
front down a few times and the masking tape will clean the seal lip of fine
crud.

If the seal is still misting, replace it before it fails in a nasty way when
your are on the brakes.

 

That is a really, really good tip. Thanks. I'll try that.

 

Hi,

I've been lurking in this group off and on, but have been riding
and wrenching on offroad bikes for 30 or so years. I was reading this
thread, and I just wanted to say that Honda doesn't think this is an
OWT. I own a KX250 and a CR125R as well as a CR85, and all these bikes
have screws on the top of the forks to release the air pressure between
motos. (According to the Manuals)

I've as far as cleaning dirt out of the seal, I've done this many
times, it doesn't always work, and when it doesn't the seals need
replacing, but sometimes when forks start to weep after being at a mud
race, it can be very useful. I use small strips of heavy paper to do the
actual cleaning.

Thx
Hans