Fork Bleeders…Yes or No??

[Nick JacksonMember]

I have done 3000km in 10 months with screw in bleeders and no seal problems.

[alanMember]

LC4skin wrote:

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Do you guys with conventional forks blow seals very often?

the seals in conventional forks last heaps longer but have there downfalls ie the old bikes there fited to :laugh:

[Steve WyethMember]

Nickj wrote:

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Do you think the air that’s being sucked in and pressurizing the fork would effect front end handling?

It will make your fork much harsher feeling. The oil in the fork is used to create resistance as it pushes through your valve, this resistance, combined with the spring (pushing the other way)effects the compression of your fork. Liquids are not compressible so the the action is very smooth and linear through the stroke.

The other element is the air gap that is run in the fork. This is the difference between the oil level and the top of your fork. The air gap provides an additional level of spring but because air is a gas it’s compressible. The result is that the air will compress as the fork moves through it’s travel (it has nowhere to go between the oil and fork tube and the pressure of the air builds (very quickly). It is this same pressure, along with the action of the spring that forces the fork to extend back to it’s normal position (rebound circuit).

The air gap should be set at atmospheric pressure, that basically means with the forks fully extended. If you bleed the screws with the forks partially compressed you effectively are reducing the air gap and the travel of your forks as the they will not want to travel back to full extension due to the vacuum effect.

Cheap fork bleeders (I have motion Pro ones on my 450 and they suck air) can act like a 1 way valve sucking air into your fork on the rebound stroke but not releasing it (pushing it out) on the compression stroke. The nett effect is that the pressure builds up in the air chamber increasing resistance to the compression stroke and making your forks feel harsh.

In summary, cheap ones will cause more harm than good, if you can guarantee decent ones won’t pass air (either way) then they would be the go.

This is my view of what happens, if you don’t like it, tough

[Bruce CurtisMember]

Air pressure as stated by my learned comrades can turn good forks into pigs in a flash, re: forkseals, both Yamaha and KTM have issues with the stock seals, a good suspension man will it the atermarket ones that don’t leak, mine have these now and not a dribble even in basketball rock gardens or let tied down for 24 hrs, zilch, nuthing, nada…

But always remember the air presurises due to heat, if you don’t bleed them at ull extension like TB said when cooled off you may have a vacuum and that sucks too.

[Nick JacksonMember]

I took my bleeders of before going to work this morning and after reading your explanation Moto feel it was the best thing to do. Thanks for a good explanation on how it all works!

[dennis da menaceMember]

so which aftermarket brand are the good ones???

[Steve WyethMember]

TB recommends his so would be worth a go if he divulges the information. Mine are Motion Pro and I wouldn’t recommend them. That’s one of many of the list.

[DobboMember]

moto wrote:

Quote:

Nickj wrote:

The air gap should be set at atmospheric pressure, that basically means with the forks fully extended. If you bleed the screws with the forks partially compressed you effectively are reducing the air gap and the travel of your forks as the they will not want to travel back to full extension due to the vacuum effect.

As was mentioned above,
I have been reading this thread, and it appears that you guys are bleeding your forks whilst on the bike or with the bike sitting on the ground.
My understanding is the front of the bike (forks) must be supported so as there is no downward pressure; or else when you bleed it you are effectively reducing the air space.
I am assuming that fork bleeders are same!

[Nick JacksonMember]

dobbo wrote:

Quote:

moto wrote:

Quote:

Nickj wrote:

The air gap should be set at atmospheric pressure, that basically means with the forks fully extended. If you bleed the screws with the forks partially compressed you effectively are reducing the air gap and the travel of your forks as the they will not want to travel back to full extension due to the vacuum effect.

As was mentioned above,
I have been reading this thread, and it appears that you guys are bleeding your forks whilst on the bike or with the bike sitting on the ground.
My understanding is the front of the bike (forks) must be supported so as there is no downward pressure; or else when you bleed it you are effectively reducing the air space.
I am assuming that fork bleeders are same!

I would only bleed the air when the front wheel was suspended, the problem I found was the bleeders were drawing in air and pressurizing the fork causing handling problems.

I have now ditched the bleeders and the front end is much more predictable and when I loosen the screw a fraction of the air is released compaired to when I had the bleeders.

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