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Old April 16th, 2013, 07:02 PM   #1
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Fork Seal Leaking

So they're leaking again.

I'll start from the top.

First, I've bought some race tech gold valve and race tech spring. I have a friend that repair motorcycle as a living, so he did the installation for me.
He put some new fork seal when he put the fork back on the bike. But they started leaking a short time after the rebuild.
He said, sometimes you can get a set of bad seals, so he took the back the bike and change the seal again.

Then, they started leaking again, he was very puzzled, but said nothing, took the bike back again, he even bought a new tool to install the seal (he thought it could have been the problem since he had it for quite sometime).

I rode it a bit after the change and winter came...

I took the bike out since its riding season again...

Someone came to see my bike tonight and he noticed that the seal was leaking. What, again?

So, can you help me figuring out what could be the problem.

Bad installation? My friend is very meticulous...
Bad seal? He uses OEM ones.
Too much oil in the fork? I have to check back with him to know how much he put and if he calculated the height with the spring and the valve inside.
Other idea?

Once I'm here. Since I'm a francophone, I might have some trouble understanding technical stuff that might gets complicated, like figuring out how to calculated the relaxed preload and actual preload. Why do I need to calculate that? Does it have to do with the recommended preload for my weight?

Since we all own Ninja 250R, we should have the same relaxed preload and actual prelaod? If we both use race tech spring. Did someone calculated it already? Once we know that number what do we do with it?

Sorry for all of those questions, but if I could get my fork set right and if i could solve the leaking seals, it would make life a little better.

If I'm all wrong about the preload thing and if you're patient to write something very "newbee proof", I'll be more than happy to read it.

Once again, thanks for your patience and help.
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Old April 16th, 2013, 07:11 PM   #2
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try another mechanic?
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Old April 16th, 2013, 08:46 PM   #3
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The first DIY on here was by a guy who had a burr or something causing his. Factory defect. You may have one as well.

Also, are the tubes pitted?
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Old April 17th, 2013, 04:32 AM   #4
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Quote:
Originally Posted by CZroe View Post
The first DIY on here was by a guy who had a burr or something causing his. Factory defect. You may have one as well.

Also, are the tubes pitted?
I'll him to take a look, but the "original" seals were fine before he installed the race tech components and before putting the last set of seals, he inspected the tube to be sure nothing could damaged them. But I'll ask him to check them again.

Thanks for your input.

As for changing the mechanic, it's an option. I'll let him go through everything again, since we're not fully bilingual, he might a misinterpreted something in the instructions.
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Old April 17th, 2013, 05:59 AM   #5
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Quote:
Originally Posted by broken neck View Post
S..........So, can you help me figuring out what could be the problem.

Bad installation? My friend is very meticulous...
Bad seal? He uses OEM ones.
Too much oil in the fork? I have to check back with him to know how much he put and if he calculated the height with the spring and the valve inside.
Other idea?
Thomas,

I would say seals and installation are not to be blamed after the second occurrence.

The problem may be in the surface of the forks on which the seals slide.

The way these seals work:
There is a delicate lip of neoprene that needs to keep certain level of pressure over the sliding surface to avoid the internal pressure of the oil to induce a leak.
That pressure comes from an annular spring (not always) and the geometry and flexibility of the lip of the seal, which uses the internal pressure to proportionally create more lip pressure.
They most achieve a balance between flexibility to conform to the surface and rigidity to stand the high internal pressure.

http://www.motoobsession.com/MO_Tech...l-leakage.aspx

Now, if the sliding surface is not smooth (dents, scratches, grooves), some oil will escape under the lip and through the valleys of those imperfections (which at the same time will erode the lip).

Also, if the tube of the fork is not perfectly round, the seal will have a hard time following that geometry (remember, their flexibility is limited by the structural rigidity) and leaks will occur.

Forks that are bent, or that have been bent and straighten up are not perfectly round anymore.
Luckily, that is an easy measurement to do with a caliper.
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Old April 17th, 2013, 10:11 AM   #6
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Thanks Hernan,

Very interesting articles.

I never gave attention to the "out of round thing" or the "over worn components", since the bike is almost new (6 000 km about 3750 miles on it), I bought it new. I've laid it down, never been involved in a crash, so the fork should be still good for sealing.

But, it could happen, I'll talk about it tonight when I'll drop my Ninjette at my friend's loft.

Could we get the tube out of round just be disassembling it?

Thanks again,
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Old April 17th, 2013, 10:38 AM   #7
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Quote:
Originally Posted by broken neck View Post
..........Could we get the tube out of round just be disassembling it?

Thanks again,
No, the tube is really strong and it takes a good fall or crash to deform it; hence, it is not probable in your case, but worth verifying it.

Look for fork's surface blemishes.

You are welcome
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Old April 17th, 2013, 10:53 AM   #8
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check for pitting on the chrome tubes and for roundness and make sure they are not bent.

Make sure the lowers/sliders are not bent and have no dirt.
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Old May 16th, 2013, 07:20 AM   #9
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A little update,

After looking at them more carefully, we think it's the chrome plating that is worn out. When we pass our hands on the upper tube, we can feel very small streaks runing up and down the tubes and allround them.

We'll try to get an estimate to have them rechromed vs. new OEM tube.

We are very surprised finding these wear marks on such a low mileage motocycle...

Thanks for the hints on looking at the finish of the upper tubes...
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Old May 16th, 2013, 07:58 AM   #10
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Could just pick up an used set instead of just buying new.
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Old May 16th, 2013, 08:39 AM   #11
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......We are very surprised finding these wear marks on such a low mileage motocycle...
http://faq.ninja250.org/wiki/Can_I_g...ors/gaiters%3F

Buds' guts are very corrosive
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Old May 16th, 2013, 10:01 AM   #12
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Quote:
Originally Posted by cuong-nutz View Post
Could just pick up an used set instead of just buying new.
Well, buying those used could be a head or tail decision, will they last 5 years, 4 months or 3 days?

Having them rechromed might give me the confidence that they will last longer.

Buying new, could give the same confidence, but being desapointed by OEM, It might always in the back of my mind...
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Old May 16th, 2013, 10:04 AM   #13
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Quote:
Originally Posted by Motofool View Post
I gave a thought about getting "gaiters", but this would bring me back in my early days of mountain biking, when every forks wore those...

Excuse me, but I think my french canadian side don't get the "bud's gut" thing... héhéhéhéhéhéhéhéhéhé...
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Old May 16th, 2013, 10:11 AM   #14
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......Excuse me, but I think my french canadian side don't get the "bud's gut" thing... héhéhéhéhéhéhéhéhéhé...
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Old May 16th, 2013, 10:34 AM   #15
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Ohhhhhhh...

You meant "Bugs" instead of "Buds"... Now I understand... I tried to figure out what budweiser guts would mean...
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Old May 16th, 2013, 10:37 AM   #16
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Old June 2nd, 2013, 11:40 AM   #17
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Another update on my fork tubes,

Finally, the guy at the chrome shop said that the chrome was to thin to be "rechromed".

I didn't want to put new tube in there, to expensive for the moment.

So I went to a bike shop and the fine sanded the tubes. They came out great...

We put new everything in there, oil seals, dust seals, inner and outer bushings. After two weeks and almost 1 000 km, nothing is coming out of there. Just have to figure out what to do to get my fork work properly with the race tech springs and valves.

Hope this will conclude my leaking fork for a long while...
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