Topic: Leaky Tach Cable at Valve Cover

[Old Scrambler]

I replaced the oil seal on the tach-drive on my CB750 K3........it still leaks at high RPMS.  Can I install a small O-Ring for an additional seal........or what?

[Gordon]

Is it possible you installed it upside down or gouged the mating surface when removing the old one? 

I've never done this before, but it's been said here several times that the tach cable oil seal from a dohc model is slightly larger and works better than the stock one.

[Johnie]

+1 Gordon. The other seal is tighter. I used it and the area has not been cleaner.

[Popwood]

Yes, Gordon, and many of us have seen others post about the 650 seal being a tad larger and fixing the leak problem. Could be it. But, what is this condition of your tach cable where it leads into the connection? If there's any crack or opening in the sheath oil will leak. I had replaced my seal with the regular one and still had the leak. On further inspection found a break in the sheath. Replaced the cable and no more leak.

[Old Scrambler]

Thanks for the tips..............No break in the sheath...........I'll try the larger seals.  It only leaks when I get the rpms above 4500 to keep up with the fastest traffic on the local commuter routes. I was careful when I removed the old unit after practicing on a parts motor. Its just annoying to find that the new seal is no better than the old original.