Quote:
Originally Posted by broken neck
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?
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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.