Hi, this is a different Mike here. :-) I was for many years a Honda dealer tech, and back in 1977 a visiting service rep (it was Fred Germain) told me that these engines were destined to consume valve guides at a rapid rate. He communicated that the factory was making a "delta change" to the valve guides. That is, their specification was changing with no notice being made to the dealer (not even the part number). The new guides, he said, would be identifiable by having a larger hole (all Honda valve guides are sold under-sized and must be reamed to size after installation), and to check all guides going into these engines with a certain size (a letter size, as I recall) drill bit. The bit would pass through an updated guide but not through an older one. The deal was, the new guides were harder and because of this were pre-reamed, and thus larger than the old-style guides that had to be reamed to size. Oddly, we didn't see a lot of this problem, even though I worked on a
bunch of black F models back then. But when I joined American Honda in 1980 as a warranty analyst, a surprising number of these engines were still being warrantied for this problem (probably ten or more a month for the first year I was an analyst -- even though the machines were by then well out of their 6-month
warranty term). Interestingly, nearly twenty years later, I would be working at an independent shop in Arizona, and during a routine head gasket replacement I would remember this and sure enough, I amazed my boss by predicting that the exhaust guides would be trash on this 6,000 mile engine, and they definitely
were. Hour-glassed. Valves rattling around in the guides like a pencil in a coke bottle. The early CB650 has the same problem, for the same reason -- altered valve geometry. :-)
