Problem is, those o-rings only last another maybe 10,000 or 15,000 miles even after you replace them.
I've heard talk of people using better quality o-rings that don't decay as rapidly as the OEM o-rings. Perhaps they were viton?
I have a theory that this may be related to hotter running temperatures on the 77 and 78 models due to the "lean-burn" carburetors. I went to great lengths to re-jet my bike so that it ran as cool as possible (much cooler than stock). I don't yet know the long-term effects of the cooler running on those o-rings. See the jetting link in my sig for cooler running info.
If you have had this o-ring problem, can you please post your year and perhaps any pertinent jetting information? Pods or airbox? stock exhaust or 4->1? Did the o-ring failure follow soon after any jetting-related changes such as adding an aftermarket pipe or muffler?
I'll start:
* 1977 CB550K bought with 13126 mi.
PD46C carbs
stock jetting
o-rings NOT LEAKING YET
RIDDEN IN EXTREME CONDITIONS, 100F+ in summer in nasty city stop-and-go traffic, and as cold as 6F in winter.
* 15,825 mi. had stock mufflers with one rotted through at about 16,000 miles, replaced with MAC 4-1.
* Started leaking oil around 20,000 mi.
* 23,358 mi. replaced paper air filter with UNI foam filter in airbox.
* 24,515 mi. oil leak became unbearable any longer, so I replaced head gasket with Vesrah set. (1997)
* 26,453 mi. Installed EMGO pods.
* 26,468 mi. re-jetted to 105 mains, optimized for best "seat of pants" tuning and lowest running temps of 303F at head gasket and 278F at base gasket. (2007)
* I've had no head-gasket o-ring failure since then, but who knows when it will fail again? Bike doesn't see those extreme conditions any longer, but also doesn't get ridden anywhere near my old daily rain-or-shine commute. Now she's a "garage queen".
