I have lost track of the number of Honda CB72-77 engines that have been rebuilt in the shop, during the past 5 years, but none have had oil leaking up the tachometer cables and then raining down on the electrics inside the headlight shell before… until now. Now, apparently it has become an infections virus or plague…
Both my 1961 CB77 and the latest 1963 CB77, bike built for my friend Lea, have similar issues; oil drooling down the tachometer cables, dripping onto the backside of the front fenders and then blowing back onto the front of the engine fins. I have studied a half dozen tachometer drive housings and bushings, but nothing of note has been observed, so far. The common denominator is that the tachometer cables are not OEM parts. Well, the black replacement cable on my bike seems to be OEM, but the aftermarket cable from my Canadian supplier is really not close to OEM specs, at all.
The large nut fitting on the cable end, which attaches to the tachometer drive bushing end, requires an oil seal which I have measured as 7x14x4. The Canadian part didn’t even have a seal or place to install one in the cable end and the one in the black OEM cable seemed to be a loose fit and obviously not blocking oil from migrating up the inner cable, inside the cable housing. After measuring the old seal and the end of the OEM cable at the 7x14x4 dimensions, the hunt was on for a replacement seal. Apparently, it isn’t a particularly common seal size and search engines came up with a Yamaha part number in that dimensional size.
A call to my favorite Honda/multi-line dealership (southbaymotorsports.com) determined that there were only 2 seals left in Yamaha’s inventories, so both were ordered. They arrived in a day and I was excited to see if this was the “solution” to the oil in the cable problem. The excitement was somewhat short-lived as the seals were somewhat loose in the cable end recess. The seals measured out something more like 13.85mm OD instead of a solid 14mm, so they were glued in with some RTV sealer. Test rides on the 1961 bike yielded oil leaks coming from the cable nut/tachometer drive bushing thread interface. A small o-ring was added to help seal the connection as the seal recess was more like 6mm deep instead of a flush 4mm depth. Another test ride revealed continuing small leaks dripping down from the threaded nut. A final try, using Teflon tape on the threads seems to have quelled the leak for now.
Ohio Cycle supplied another gray aftermarket copy tachometer cable, which had a fairly flimsy oil seal installed, so it was pried out and the second Yamaha seal was installed in its place, along with an o-ring in a spare tachometer drive unit. Some of the dimensional changes on these bikes are so subtle that the only way you know that something has changed is when it doesn’t fit in place of the original part. An inexpensive, later model, die-cast tachometer assembly was purchased from an eBay seller for testing and the depth of the well hole where the camshaft’s tach drive threads reside was just a little bit shallow and the part would not fit the 1961 cylinder head.
As a fallback position, a pair of OEM Honda tach cables were ordered from an eBay seller in Thailand and should arrive in a couple of weeks. Time will tell if this is the final solution to the “leaking fender” syndrome that is plaguing these two vintage Super Hawks.