i replaced my 03 919 forks with some f4 forks from ebay.
they were (supposed to have been) taken off of an 06 with 3000 miles. when i received them they looked like they were in good condition and they felt great on the bike.
but i noticed some residue on the left fork when cleaning it a few weeks ago. i wiped it off, and now it has re-appeared (pictured in attachment).
does this mean it is leaking oil? do the seals need replacing? what would cause this?
i try to take it easy, but my commute is pretty brutal - plenty of potholes and a few unavoidable bumps. and the 919 is heavier than an f4 (though not by very much)... is that the problem? or were they probably just shot to begin with, and mis-represented by the seller? are they ok to ride as is, or is this critical?
i would appreciate some advice on this. i swapped the forks out myself, but i have never serviced a fork, and don't know what to look for.
Very carefully pry the dust cover up. Do a visual inspection for signs of fork oil. The residue shown in your photo does not look good. Get the front end off the ground so that the wheel spins freely. Closely inspect the fork for any nicks which can cause a seal to leak. It is not normal for a seal to leak with only 3,000 miles.
Mike's right, very strange to see seals fail after only 3k miles.
But thats what it looks like. Do you have any history on the forks? If the previous owner abused the seals (slamming down from wheelies) it could cause them to fail prematurley.
The rubber seal you can see is NOT the fork seal, just a wiper. Pry it up with a screwdriver and you'll have a better idea of what your looking at.
Seal failure at this mileage or less is unusual, but not unheard of. Most commonly, damage to the hard chromed stancion tube from impacts by bits of terra not so firma, and quite a number of other hard/sharp things thrown up by the minions of Lucifer (that's cars, by the way) can cut the seals. To inspect them, clean everything with hot water, dish soap, and clean rags then wipe it down with a small amount of WD-40. Visually inspect the chrome plating to about 45 degrees each side of straight ahead, and run your fingernail up and down to catch any less visible damage. Usually, there will be a raw edge which will cut the seal. Small dings can be dressed down with oiled crocus cloth on a non flexible flat sanding block -- avoid the temptation to use any coarser grits which can leave deep scratches, and always move it up and down while working the area to create a crosshatch pattern similar to finish honing a cylinder, and for the same reasons: oil is retained in the pattern, and the seal surface is continuously lubricated. Any horizontal or vertical scratches catch the seal or provide a path for the entry of dirt and water. Past this, unless you are quite confident in your ability to tear them down and replace the seal(s), I recommend taking them to a shop which specializes in suspension work, and watch the procedures they follow -- usually, they will be happy to let you watch, but there may be a bit of a wait. Also, either buy a service manual for the forks (and unfortunately the rest of the bike), or sweet talk a dealership service manager into letting you photocopy or photograph the appropriate section of the manual.
Good luck with this.
If it has already been done, it is safe to assume it is possible to do it.
On the other hand, if it has not been done never assume it is impossible to do it.
------- Rob --------