Air build up in Forks – OLD Bull Trailriders

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September 14, 2011 at 7:16 pm #100489

Mick D
Member

Hey Rudy,
I not long ago purchased a brand new YZ250F, it now has only 14 hrs on it and on Sunday I was horrified to see oil oozing out of the left fork seal. Not something I expected from what is basically a brand new bike.

Anyhow I pulled the offending fork leg out and put it on the bench with the hope that I could run a feeler gauge around the seal and hopefully dislodge a piece of grit or the likes that I was hoping had caused the leak.

I inserted the feeler gauge and a heap of air escaped from the forks via the seal. There was a heap of pressure built up in there, which I will admit I should have released via the bleeder screws at regular intervals but I hadn’t given it a thought.

I then undid the top screw on the fork leg and more air escaped, upon that happening I thought it best I check the other fork leg. Not even the slightest hiss of air came out……..What is going on there, do you think it was excessive pressure that was forcing the oil past the seal and why would only one fork have such a big build up of air??

And another thing, I currently have 3 bikes in my shed with a blown fork seal and they are all on the brake calliper side, is this just co incidence or is it a common thing that they tend to blow on the calliper side?

September 14, 2011 at 7:38 pm #208839

Matt Baker
Member

My KTM 625 used to have heaps of air in 1 side and bugger all in the other (sorry can’t remember which one was which)

My Berg seems to get the same amount of air in each side.

Can’t explain it and always wondered why???

September 14, 2011 at 7:57 pm #208840

Alex
Member

My guess here would be the caliper side under braking load binds the forks up slightly, compressing forks as you brake. One side of the seal loads up more (rear of the seal) and as the inner tube slides up through the seal brings along some air too. Would happen more with the caliper fork because of the binding/load. Could be wrong, Evil will no doubt know best.

September 14, 2011 at 8:07 pm #208853

Jeffrey Smith
Member

I seem to recall that one of the forks on the berg always had pressure and the other side didn’t, not sure which side had the pressure though.

September 14, 2011 at 8:39 pm #208841

alan
Member

think your just unlucky mic i always seem to get blown fork seels randomly not always the brake side actualy its normaly the other side for me.on the air thing has the front wheel been sentered up properly when put on only thing i can think of .welcome to yamaha ownership and mud runs

September 16, 2011 at 1:52 am #208842

Alex
Member

So was i right or wrong? Geez.

September 16, 2011 at 4:02 am #208985

alan
Member

i got no idear

September 16, 2011 at 10:34 am #208989

Greg
Member

The Rude one maybe doing or busy with Sunny Corner :huh: Your theory is interesting to say the least Axel, without having given it much thought I like it But a theory is like an arsehole everyone has one :laugh: this arsehole doesn’t so I will go with yours

TB

September 16, 2011 at 10:43 am #208990

Adrian Lee
Member

Trailboss wrote:

The Rude one maybe doing or busy with Sunny Corner :huh: Your theory is interesting to say the least Axel, without having given it much thought I like it But a theory is like an arsehole everyone has one :laugh: this arsehole doesn’t so I will go with yours

TB

Sorry for going off topic but this is the first time ive seen TB without an opinion on something.

Are you feeling ok mate ? :laugh: :laugh:

September 16, 2011 at 10:49 am #208991

Steve
Member

I have an asshole to .Sorry a thought.Being on the disk side,you would think that the heat from the disk may transfer
to fork tube.disk brakes get bloody hot.Just a thought.mine have allways go on that side to.

September 16, 2011 at 10:52 am #208993

murph the surf
Member

I’ll also go with your theory as it is the same as mine, Axel.
I have almost 16000kms on the 525 and changed seals plenty of times.
The majority being the LH side (brake side)
Have even had to build up the area where the DU bush seats and machine it out to the correct size.
So it seems the braking side does suffer more abuse
Cheers
Murph

September 16, 2011 at 11:07 am #208994

Greg
Member

aido wrote:

Trailboss wrote:

The Rude one maybe doing or busy with Sunny Corner :huh: Your theory is interesting to say the least Axel, without having given it much thought I like it But a theory is like an arsehole everyone has one :laugh: this arsehole doesn’t so I will go with yours

TB

Sorry for going off topic but this is the first time ive seen TB without an opinion on something.

Are you feeling ok mate ? :laugh: :laugh:

Now I do have an opinion now, in my opinion your a smart arse :laugh: :laugh: :laugh: There are many a topic here I don’t get involved in because I do know, understand or couldn’t be arsed about

Back on topic

Toes I read yours and think ( there Aido ) the heat wouldn’t transfer that far maybe :blink:

TB

September 19, 2011 at 4:12 pm #208843

Mark Drinkwalter
Member

Ok, when I stopped laughing – I have given it some real thought. Air enters a fork through the seals or from some loose fastener or adjuster on the top of the fork.

A. Do you have those air bleeder thingies on all your forks?
B. If you do – stop touching them and throw them out – they are evil and should be cast out.
C. If you dont, dont buy them – they are evil and should be cast out.
D. Make sure your bleed screws are snug and the o-ring under it is in good condition.

Now in theory, with the inherent stiffness provided in modern triple clamps, large axles, wheels, spokes etc. you shouldn’t get any noticeable twist or pull from one fork leg or the other, and certainly not enough to wear one seal over the other.

So after much consideration Mick, here is my official diagnosis.

As there is no statistical deviation with leaking seals that provides evidence of your “brake” side seal wearing prematurely over the non brake side, and given the statistical abnormality that ALL of YOUR bikes leak from just the one side, I can conclude that you are indeed cursed.

Of course if you want us to look at them, shoot them over, otherwise get a witch doctor / priest / hooker to exercise out the demons in your bikes.

ER out.

September 19, 2011 at 4:51 pm #209199

Mick D
Member

Well Rudy, I will now throw another bike into the mix of the shitters I have in the shed with leaking fork seals. I have 3 bikes with leaking LH side fork seals and another has a leaking RH side seal. The latter being a Buell M2 Cyclone which has the disc on the RH side. So indeed I must be cursed to have 4 bikes with one only leaking seal and all of those being on the disc side of the forks. Weird shit indeed. :ohmy: :huh:

I actually have stopped the YZ’s fork seal from leaking, by using the feeler gauge trick and keeping on top of the air build up. It is amazing how much air will build up after just a short ride.

I was aware that most suspension guys dont rate the bleeder buttons at all, so I still run the bleeder screws.

September 19, 2011 at 5:29 pm #208844

Craig Hatton
Member

Oh evil one
How is your workload at the moment, what sort of time for the work on the front end as discussed

cheers Hatto

Sorry for hijack
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