Motorcycle Repair: Honda CB550f, shaft surface, new shaft

Question
Bill,
I just bought a 1976 Honda CB550f with just under 30K miles. The bike is all original and runs well so far. I am having trouble with a small oil leak that leaves a bit of oil on my left boot and on the gear shift lever. I can't seem to find the source of the leak. Is this a common problem? What will I need to do to fix it?
Any help you can offer would be great.
Thanks,
Matt

Answer
Matt, the shift shaft goes into the engine crankcases and there is a seal at the edge of the cases to keep the oil inside. The seal dimensions are OIL SEAL (13.8X24X5).

You will have to remove the left crankcase cover, which is located to the rear of the alternator cover. This covers the front sprocket and the area where the shift shaft seal is located. Seal replacement does require some care so you don't damage the shaft during the removal process or damage the new seal on installation. Clean the whole area completely, while you have the opportunity. Check the shaft surface to see if there is a deep groove worn into the shaft, which may cause future leaks. If worn, a new shaft will need to be installed, which requires pulling the clutch cover on the opposite side.. more seals and gaskets involved.

When you remove the cover, look carefully at the seal area to verify the leak at the seal. The other cause for oil dribbling down the shaft is excessive chain lube, which gets flung off the chain and onto the shaft. When the engine comes up to temperature, the oil often heats up and transfers down the shaft, especially when the bike is left on the side stand to cool down after a ride.

Oil seal leaks are common issues with almost any 28 year old motorcycle or car. If you are not comfortable doing this repair, have a shop perform the service for you. A lot of bike shops won't work on vintage machines, but this is a pretty straightforward repair, which should take less than an hour by a competent person.

Bill Silver