Leaking Fork Seals | ANSWERS

QUESTION: I bought a used Honda CB750 Nighthawk about six months ago. It needed fork seals when I got it, so I had them replaced by a mechanic. The left one started leaking again soon afterward. I had it replaced, but it still leaks. What’s going on here? Are Honda fork seals no good? Should I try aftermarket seals instead?

James Gatz Grand Forks, ND

ANSWER: Actually, James, Honda doesn’t make its fork seals, and the majority of the seals out there are manufactured by the same few companies. It doesn’t sound like the quality of the seals is the issue. The fact that only the left seal is leaking suggests there’s a problem on that side unrelated to the seal itself. The Nighthawk’s upper fork tubes are exposed to rocks thrown up by cars and trucks that can damage the chrome plating over which the fork seal slides. The likely culprit here is a nick or pit on the fork tube caused by something hitting the tube. As the fork seal moves up and down with the slider, the damaged spot eventually tears the seal, and the fork oil leaks out.

No matter how often you change the seals, you won’t fix the leak until you deal with the damaged fork tube. If the nick is raised above the surface of the surrounding chrome, sometimes you can remove it with a very fine-grit sharpening stone or a strip of emery cloth on a sanding block. Move the stone or cloth up and down along the tube’s length or at no more than 45 degrees to the tube’s long axis; in other words, it’s okay to “cross hatch” the tube, but don’t cut straight across. Use plenty of light lubricating oil with the stone, replace the emery cloth with a fresh strip often, and wipe the tube clean after every few passes.

A pit that’s lower than the surrounding surface is trickier. Try filling it with epoxy and sanding it down with emery cloth until you can’t feel it with your finger; we’ve also had good luck with lacquer nail polish. Be sure to get all the oil off the tube first or the epoxy won’t stick. Note, however, that if the chrome plating is missing, the metal underneath might eventually rust even with a coating of epoxy, forcing it out of the pit. If neither method works, your only recourse is a new fork tube. Either way, invest in a set of fork gaiters to protect the chrome on the fork tubes from future damage.